China's school-bus-size Tiangong-1 modular space station is expected to fall to Earth in a fiery blaze on or around Easter Sunday.

The US government is tracking the orbit of Tiangong-1 and about 23,000 other human-made objects larger than a softball. These satellites and chunks of debris zip around the planet at more than 17,500 mph — roughly 10 times the speed of a bullet.

However, there are millions of smaller pieces of space junk orbiting Earth, too.

"There's lots of smaller stuff we can see but can't put an orbit, a track on it," Jesse Gossner, an orbital-mechanics engineer who teaches at the US Air Force's Advanced Space Operations School, told Business Insider.

As companies and government agencies launch more spacecraft, concerns are growing about the likelihood of a "Kessler syndrome" event: a cascading series of orbital collisions that may curtail human access to space for hundreds of years.

Here's who is keeping tracking of space junk, how satellite collisions are avoided, and what is being done to prevent disaster on the final frontier.

SEE ALSO: A spacecraft graveyard exists in the middle of the ocean — here's what's down there

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Thousands of launches since the dawn of the Space Race have led to a growing field of space debris. Most space junk is found in two zones: low-Earth orbit, which is about 250 miles up, and geostationary orbit, about 22,300 miles up.

In addition to 23,000 objects the size of a softball or larger — like rocket stages, satellites, and even old spacesuits — there are more than 650,000 objects that are softball-to-fingernail-size.

Another 170 million bits of debris as small as a pencil tip may also exist — including things like explosive bolts and paint flecks.

Source: ESA

Countless pieces of tiny debris were added to orbit in 2007, when China intentionally smashed one of its old satellites with a "kill vehicle." Then in 2009, an old Russian satellite and US satellite collided, adding even more dangerous junk.

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• The funeral for British physicist Stephen Hawking was held on Saturday in Cambridge. 
• Hawking died at the age of 76 on March 14 after living for decades with a degenerative disease.  
• Hawking's ashes will be interred at Westminster Abbey in June, among some of the greatest scientists in history, Isaac Newton and Charles Darwin.
• The ceremony included space-themed music composed specially for Hawking called "Beyond the Night Sky," and his coffin was topped with white "Universe" lilies and white "Polar Star" roses. 

CAMBRIDGE, England (Reuters) - Well-wishers filled the streets of Cambridge on Saturday for the funeral of British physicist Stephen Hawking, hailed by another leading scientist as "an imprisoned mind roaming the cosmos".

Hawking, crippled since a young man by a degenerative disease, beat the odds stacked against him to became the most celebrated scientist of his era. His work ranged from the origins of the universe itself, through time travel and probing black holes in space.

He achieved international renown after the publication of "“A Brief History of Time" in 1988.

His coffin was topped with white "Universe" lilies and white "Polar Star" roses and carried by pallbearers from the University of Cambridge, where he worked. It was greeted by a large crowd outside the church who clapped as it was carried in.

The 76-year-old scientist was mourned by his children Robert, Lucy and Timothy, joined by guests including playwright Alan Bennett, businessman Elon Musk and model Lily Cole.

Eddie Redmayne, the actor who played Professor Hawking in the 2014 film "The Theory of Everything" was one of the readers in the ceremony and Felicity Jones, who played his wife, Jane Hawking in the film also attended the service.

The ceremony included space-themed music composed specially for Hawking called "Beyond the Night Sky", inspired by a poem and quotes from "A Brief History of Time" and whistling and "shh" sounds based on recordings of space.

Astronomer Royal Martin Rees, a personal friend, read from Plato's Apology 40, "The Death of Socrates", which talks of the search for knowledge persisting after death.

Confined to a wheelchair for most of his life after being diagnosed with Motor Neurone Disease when he was 21, Hawking's towering intellect and sheer persistence struck a chord with ordinary people, Rees said in an appreciation published earlier this month.

"Why did he become such a 'cult figure'? The concept of an imprisoned mind roaming the cosmos plainly grabbed people's imagination," he said.

"His name will live in the annals of science; millions have had their cosmic horizons widened by his best-selling books; and even more, around the world, have been inspired by a unique example of achievement against all the odds – a manifestation of amazing will-power and determination."

Hawking's ashes will be interred at Westminster Abbey in June, among some of the greatest scientists in history, Isaac Newton and Charles Darwin.

Writing by Elisabeth O'Leary; Editing by Stephen Powell.

SEE ALSO: Stephen Hawking was my real-life Time Lord: Remembering the genius who inspired countless humans on this rock drifting through space

DON'T MISS: 15 of the most remarkable and memorable things Stephen Hawking ever said

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• Neutron stars that crash together in space forge valuable metals like silver, gold, and platinum.
• Some heavy periodic elements may be created almost exclusively by such cosmic crashes.
• Europium, one of the least-common elements in the universe, is a candidate and is used in TVs, lasers, and plastics.
• A neutron-star collision discovered through gravitational waves made about 1-5 Earths' worth of the europium, according to a new study.

In October 2017, astrophysicists announced a remarkable discovery: The first-ever detection of two dead stars smashing together.

The collision created gravitational waves, or ripples in spacetime, which were "heard" by the LIGO experiment. But the event — unlike merging black holes— threw off gobs of neutrons (essentially super-heavy-element barf).

This material almost immediately decayed into lighter elements, leading to a bright, radioactive "kilonova" astronomers could see some 85 million to 160 million light-years away from Earth. Light from the energetic breakdown of this material suggest that it led to the unimaginably valuable formation of about 50 Earth masses' worth of silver, 100 Earth masses of gold, and 500 Earth masses of platinum.

Researchers who've pored over the data since last year now think the collision also made 1-5 Earth masses of a very rare element called europium, according to a recent study in The Astrophysical Journal. (They also dialed back the gold-formation estimate to 3-13 Earth masses worth.)

The study could mean that neutron-star collisions are responsible for forging most of the europium and gold we find on Earth, not to mention other key elements.

What europium is and how it's made

Europium is element number 63 on the Periodic Table, and it's a somewhat hard, silvery metal that reacts with oxygen and water — so it's never found in pure form. When it is pure, it's stored in inert gases (e.g. argon) to prevent it from oxidizing and tarnishing.

The element is used to make some red lasers, electronic parts, and the red phosphors of cathode-ray-style television sets. (One estimate suggests there's 0.5-1 gram of europium in every CRT screen.) Its ability to react to ultraviolet light also makes it an anti-counterfeit measure in euro paper currency.

Europium is also seeing newfound use in ultra-bright-red LEDs and — if the technology pans out — could lead to a stable quantum hard drive.

Researchers suspected europium was formed by colliding neutron stars, but couldn't be sure how much until one was detected. Another explanation is that cataclysmic explosions of stars, called supernovas, form most europium and other elements heavier than nitrogen.

A bit of nuclear alchemy called the rapid process or r-process is what drives the creation of such heavy elements.

The r-process goes something like this: As neutron stars move toward each other, a tiny bit of their material gets shot into space at incredible speeds. Those neutrons are very hot and crowded, so they smash together while moving outward, forming giant atomic cores.

Because very big atoms are highly unstable, they almost immediately break apart and decay into smaller atoms — stuff like platinum, gold, silver, and europium.

Fortunately, we don't need a spaceship to find this stuff created by neutron stars — it's here on Earth. Countless smash-ups over the millennia spread around enough of these exotic metals that when our planet formed, they were baked right into its crust.

"The rate of these neutron star mergers in our galaxy is about one every 100,000 years. On human time scales, that's a long time," Duncan Brown, an astronomer at Syracuse University who's a member of the LIGO research collaboration, previously told Business Insider. "But on galactic time scales, when you're creating stars and solar systems, that's not that much time."

What's still uncertain is how much colliding neutron stars might contribute to europium. If LIGO finds more and more colliding neutron stars over the years, it's likely those events — not supernovas — are where the most valuable materials on the planet come from.

SEE ALSO: Scientists cracked one of Einstein's greatest mysteries — now a bizarre new form of astronomy is emerging

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NOW WATCH: Scientists won the Nobel Prize for detecting gravitational waves — here's why that matters

Albert Einstein died on this day 63 years ago, but he remains one of the greatest minds of the 20th century. His contributions to human knowledge are unparalleled.

The physicist conducted groundbreaking research on how our universe functions, formulated the Theory of Relativity, and predicted the existence of gravitational waves a century before we observed them.

Einstein wasn't just brilliant, he was deep: a scientist-philosopher who knew just how to describe the human condition. That genius, combined with the human highs and lows Einstein witnessed during his lifetime, made for a perspective on life that's yet to be matched.

We've compiled a list of Einstein's 15 best quotes, which teach us about the mind, learning, and that crazy thing called life.

Sean Kane contributed to an earlier version of this story. 

SEE ALSO: How Einstein became a suspected spy in a clip from the new TV show 'Genius'

On the passing of time

On being happy

On education

• Russian President Vladimir Putin said in early 2018 that Russia was developing a nuclear-powered torpedo that carries a "massive"nuclear weapon.
• Videos posted to the Russian Ministry of Defense's YouTube account appear to show a prototype of such a torpedo codenamed "Poseidon."
• If Poseidon is ever completed, it might be able to create a 300-foot tsunami if exploded at some coastal locations.
• One arms control experts described such a hypothetical weapon as a "doomsday machine," saying it could spread unprecedented and long-lived radioactive fallout.
• But one nuclear-weapons researcher previously said such a weapon would be "stupid," as it'd greatly limit its explosive power and fallout compared with detonating a similar device in the air.

Shortly after US President Donald Trump spoke with Russian president Vladimir Putin in what became an controversial meeting, the Russian government published several videos that appear to show off a host of new nuclear weapons systems.

One particular video stands out among the other alleged weaponry, though: an alleged prototype of a giant torpedo some experts have dubbed a "doomsday" machine.

Putin first publicly described such a nuclear-powered device on March 1 during an address to the Russian Federal Assembly. He said the autonomous drone would quietly travel to "great depths," move faster than a submarine or boat, "have hardly any vulnerabilities for the enemy to exploit," and "carry massive nuclear ordnance," according to a Kremlin translation (PDF) of Putin's remarks.

"It is really fantastic," Putin said, adding: "There is simply nothing in the world capable of withstanding them."

Putin also claimed Russia finished testing a nuclear-powered engine for the drones in December.

"Unmanned underwater vehicles can carry either conventional or nuclear warheads, which enables them to engage various targets, including aircraft groups, coastal fortifications, and infrastructure," he said.

Videos that Putin presented in March were primarily computer renderings, and he did not refer to the device by name in his speech.

However, the Russian Ministry of Defense on July 19 uploaded several new clips to its YouTube account that may show real-world hardware — including one of a torpedo-shaped device called "Poseidon."

Defense analyst H.I. Sutton wrote in a blog post that the prototype in the new video is "generally consistent" with Russia's prior depictions of a giant, nuclear-powered, nuclear-weapon-armed autonomous submarine that also goes by the code names Oceanic Multipurpose System Status-6, Skif, and Kanyon.

Based on still images from the video, Sutton figures it's about 2 meters (6.5 feet) wide and 20 meters (66 feet) long with room for a nuclear reactor in the center and a large thermonuclear warhead toward the front.

The Russian government reportedly leaked a diagram of such a weapon in 2015 that suggested it would carry a 50-megaton nuclear bomb about as powerful as Tsar Bomba, the largest nuclear device ever detonated.

The Trump administration even addressed the possible existence of the weapon in its most recent nuclear posture review.

Nuclear physicists say it could cause a local tsunami, though they question its purpose and effectiveness, given the far more terrible destruction that nukes can inflict when detonated aboveground.

Why the Russian 'doomsday' device could be terrifying

A nuclear weapon detonated below the ocean's surface could cause great devastation.

US nuclear tests of the 1940s, '50s, and '60s, including the underwater operations Crossroads Baker and Hardtack I Wahoo, demonstrated why.

These underwater fireballs were roughly as energetic as the bombs dropped on Hiroshima or Nagasaki in August 1945. In the tests, they burst through the surface, ejecting pillars of seawater more than a mile high while rippling out powerful shockwaves.

Some warships staged near the explosions were vaporized. Others were tossed like toys in a bathtub and sank, while a few sustained cracked hulls and crippled engines. Notably, the explosions roughly doubled the height of waves to nearby islands, flooding inland areas.

"A well-placed nuclear weapon of yield in the range 20 MT to 50 MT near a sea coast could certainly couple enough energy to equal the 2011 tsunami, and perhaps much more," Rex Richardson, a physicist who researches nuclear weapons, told Business Insider in March, referring to the Tohoku earthquake and tsunami that killed more than 15,000 people in Japan.

"Taking advantage of the rising-sea-floor amplification effect, tsunami waves reaching 100 meters in height"— about 330 feet — "are possible," he said.

Richardson and other experts have also pointed out that a near-shore blast from this type of weapon could suck up tons of ocean sediment, irradiate it, and rain it upon nearby areas — generating catastrophic radioactive fallout.

"Los Angeles or San Diego would be particularly vulnerable to fallout due to the prevailing onshore winds," Richardson said, adding that he lives in San Diego.

The problem with blowing up nukes underwater

Greg Spriggs, a nuclear-weapons physicist at Lawrence Livermore National Laboratory, said a 50-megaton weapon "could possibly induce a tsunami" and hit a shoreline with the energy equivalent to a 650-kiloton blast.

But he has said it "would be a stupid waste of a perfectly good nuclear weapon."

That's because Spriggs believes it's unlikely that even the most powerful nuclear bombs could unleash a significant tsunami after detonating underwater, especially miles from shore.

"The energy in a large nuclear weapon is but a drop in the bucket compared to the energy of a [naturally] occurring tsunami," Spriggs told Business Insider in 2017. "So any tsunami created by a nuclear weapon couldn't be very large."

For example, the 2011 tsunami in Japan released about 9.3 million megatons of TNT energy. That's hundreds of millions of times as much as the bomb dropped on Hiroshima in 1945 and roughly 163,000 times as much as the Soviet Union's test of Tsar Bomba on October 30, 1961.

Plus, Spriggs said, the energy of a blast wouldn't all be directed toward shore — it would radiate outward in all directions, so most of it "would be wasted going back out to sea."

A detonation several miles from a coastline would deposit only about 1% of its energy as waves hitting the shore. That scenario may be more likely than an attack closer to shore, assuming US systems could detect an incoming Poseidon torpedo.

But even if such a weapon were on the doorstep of a coastal city or base, its purpose would be questionable, Spriggs said.

"This would produce a fraction of the damage the same 50 MT weapon could do if it were detonated above a large city," Spriggs said. "If there is some country out there that is angry enough at the United States to use a nuclear weapon against us, why would they opt to reduce the amount of damage they impose in an attack?"

Why would Putin develop a 'doomsday machine'?

Putin said in March that Russia had tested a nuclear power unit that "enabled us to begin developing a new type of strategic weapon" to carry a huge nuclear bomb.

If ever realized, it's join thousands of nuclear weapons in Russia's arsenal.

In a 2015 article in Foreign Policy, Jeffrey Lewis, an expert on nuclear policy at the Middlebury Institute of International Studies, dubbed the hypothetical weapon "Putin's doomsday machine."

He wrote that there was speculation that the underwater weapon might be "salted," or surrounded with metals like cobalt, which would dramatically extend fatal radiation levels from fallout— for at least several months, or possibly even decades — since the burst of neutrons emitted in a nuclear blast could transform those metals into long-lived, highly radioactive chemicals sprinkled all over.

"What sort of sick bastards dream up this kind of weapon?" Lewis wrote, noting that such salted weapons were featured in the 1964 science-fiction Cold War parody film"Dr. Strangelove."

Like the blast energy, though, Spriggs said bomb fallout — also called "source term" in nuclear physics parlance — from an underwater explosion would be dramatically reduced.

"In reality, the vast majority of the source term will never escape from the ocean as air-borne particles," Spriggs told Business Insider in an April 2018 email. "Most of the fission products and activation products that are thrown into the air during the explosion will be trapped in the water droplets in the water spout and will fall back to the ocean within just a few 1000 ft from the detonation point. Only a very small fraction, if any, of the source term will remain in the air and/or 'surf' on the wave that eventually strikes the shoreline."

But with an airdrop, he added "almost 100% of the source term [...] ends up on the land"— so a salted weapon blown up over a target would "be many, many orders of magnitude worse than the fallout produced by an underwater detonation" several miles from shore.

To Lewis, it doesn't necessarily matter whether the nuclear torpedo will be completed or some advanced posturing designed to prevent the US from attacking Russia or its allies.

"Simply announcing to the world that you find this to be a reasonable approach to [nuclear] deterrence should be enough to mark you out as a dangerous creep," he said.

This story was originally published on April 24, 2018. It has been updated with new information.

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NOW WATCH: Here's how easy it is for the US president to launch a nuclear weapon

• Stephen Hawking's final paper was just published in the Journal of High Energy Physics.
• The paper predicts there are not infinite parallel universes in the multiverse, but instead a limited number.
• These universes would have laws of physics like our own, the paper says.
• It also explains how we might be able to see proof of this theory and find evidence for parallel universes by finding gravitational waves.

Ten days before he died, theoretical physicist Stephen Hawking submitted a final paper for publication.

That paper — titled "A smooth exit from eternal inflation?" — has now been published in the Journal of High Energy Physics. In it, Hawking and coauthor Thomas Hertog lay out a theory on the origin of the universe that might settle a few lingering questions.

One popular understanding of the Big Bang suggests that our universe is one in a "multiverse" of infinite parallel universes. The paper posits that the other universes out there follow the same laws of physics that exist in our universe.

This makes the number of possible universes much more manageable and testable, since it's no longer an effort to understand infinite universes that could have different underlying rules of physics and chemistry.

"We are not down to a single, unique universe, but our findings imply a significant reduction of the multiverse, to a much smaller range of possible universes," Hawking said in a statement last fall.

The paper also implies that it might be possible to test this theory. Physicists could look for evidence of other universes using tools designed to measure ripples in spacetime — also known as primordial gravitational waves — that would have been generated by the universe's initial expansion from the Big Bang.

Inflation that never stops

Hawking helped develop the theory that led to the idea of infinite parallel universes.

That concept relies on something known as "eternal inflation." The thinking, in essence, is that after the Big Bang, the universe — or all the universes — started to expand, but that process never stopped in some places. Our universe, by that logic, is just one pocket where that exponential inflation stopped and stars and galaxies formed. (Our universe is still expanding, but not in that rapid way.)

"The usual theory of eternal inflation predicts that globally our universe is like an infinite fractal, with a mosaic of different pocket universes, separated by an inflating ocean," Hawking said in an interview last fall, according to the University of Cambridge.

"The local laws of physics and chemistry can differ from one pocket universe to another, which together would form a multiverse. But I have never been a fan of the multiverse. If the scale of different universes in the multiverse is large or infinite, the theory can’t be tested."

Hertog told Cambridge that the physics that would account for infinite parallel universes break down when applied to the theory of eternal inflation.

A boundary to eternal inflation

Hawking and Hertog's new paper relies on string theory, a branch of physics that tries to reconcile quantum physics with gravity and Einstein's theory of relativity. They came up with a new idea of eternal inflation that relies on a boundary at the beginning of time.

"When we trace the evolution of our universe backwards in time, at some point we arrive at the threshold of eternal inflation, where our familiar notion of time ceases to have any meaning," Hertog told Cambridge.

Starting from that boundary, the new theory predicts a finite structure of universes emerging from the Big Bang.

If this theory is proved true, it would suggest that other universes like our own could have emerged at that point. And there could even be primordial gravitational waves that match the inflation of the universe. But this new model is still far from proven, and physicists will need more data and a better understanding of string theory before that's possible.

The existing instruments used to look for gravitational waves are probably not sensitive enough to find evidence of this theory, according to Hertog. But planned future instruments like the European space-based LISA gravitational wave observatory might be.

If we can detect that evidence, we'll better understand how our universe and its laws came into being after the Big Bang — and we might know more about whatever other universes are out there.

SEE ALSO: 15 of the most remarkable and memorable things Stephen Hawking ever said

Join the conversation about this story »

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There is something gravely wrong with the ultimate fate of the Death Star, a moon-size weapon in the "Star Wars" movies, and physicists think you should know about it.

The Death Star meets its final doom in "Return of the Jedi," the epic conclusion to the original "Star Wars" saga.

The colossal ship is orbiting the forested Sanctuary moon of the planet Endor and, after it's blown up, the Rebel Alliance and its hairy Ewok friends party in the trees. Everyone and everything is hunky-dory.

But ask a physicist — or a dozen, as we've done — what happens when you detonate a giant metal sphere above a lush green world. The answer is downright chilling.

"The Ewoks are dead. All of them," said one researcher and self-professed "Star Wars" fan, who wrote a white paper in 2015 that supported his conclusion.

Each scientist who responded to our emails quibbled over the exact details, yet a strong consensus emerged in support of a popular fan theory: The "Endor Holocaust" is inevitable, and that would be a threat to the plausibility of any future movies (galactic bankruptcy be damned).

Here's why.

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The "Endor Holocaust" fan theory dates back to 1997, when it first appeared on a website called TheForce.net. Curtis Saxton, an astrophysicist and "Star Wars" super-fan, wrote it as part of a technical series that analyzes the movies frame-by-frame with scientific rigor.

Source: TheForce.net

Saxon's 10,000-word essay about the Endor holocaust claims that the doom of Endor and the cuddly, warmongering Ewoks who live there "is an inevitable consequence of observable facts."

The rebels' attack on the Death Star turns it into fine metallic bits, Saxton argues. The debris then rains down on Endor, burns up into a toxic sooty fallout, and sparks global firestorms.

But many of Saxton's various measurements are open to interpretation, since depictions of the Death Star, Endor, and other details are inconsistent from one scene to the next.

Source: TheForce.net

Every two years, the National Science Foundation is required to tell the president how the US is doing in regard to science and engineering.

"As economies worldwide grow increasingly knowledge-intensive and interdependent, capacity for innovation becomes ever more critical," the NSF says in its latest report, titled "Science & Engineering Indicators 2018."

The news is OK, but not great. Americans are increasingly interested in environmental issues, the report says, and relative to previous years, they're expressing more concern about climate change and humanity's role in it. They also trust scientists more than roles in any other institution aside from the military.

But the US lags behind dozens of countries in the rate of awarding bachelor's and advanced degrees in science, technology, math, or engineering.

The American public also isn't doing much better on 10 simple questions the NSF asks to test the public's understanding of science.

Scroll down to see the questions the NSF asked for the latest report, see how many answers you can get right, and then compare how 11 countries who asked the same science questions performed. 

Kelly Dickerson contributed to this post.

SEE ALSO: 17 'facts' about space and Earth that everyone says but are actually wrong

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Question 1:

The correct answer...

Scientists estimate that Earth's core is more than 10,000 degrees Fahrenheit — nearly the temperature found on the surface of the Sun.

How the US and other nations did:

After a long work day, most of us happily collapse into a couch and binge-watch our favorite show.

But Linden Gledhill, a Philadelphia-based pharmaceutical biochemist, retreats to his basement lab. There, he builds custom gear so that he can record the beautiful, complex, and sometimes very weird intersection of science, art, and nature.

For example, Gledhill hacked an old hard drive into a camera shutter 10 times faster than anything in a store. He's also rigged up a machine to create snowflakes on demand and patented a super-resolution photography rig.

Gledhill uploads his experimental photos and video to Flickr, and art directors and producers take notice — not only because he's creative, but also because he's good. He's earned commissions for TV commercials and music videos, and most recently, high-tech prints of his photos were donned by fashion models.

For the past couple of years, Gledhill has been playing with a tiny dish of liquid that sits on a speaker. Called a cymascope, it's designed to create and tune repeating patterns of waves, like those formed in wine by rubbing the rim of a crystal glass to make it vibrate or "sing." These cyclical ripples, also called cymatics, travel far faster than human eyes can see, so he uses ultra-high-frame-rate cameras slow them down and record their secrets.

"It allows you to see the individual vibration states throughout the cycle. That's pretty cool. Typically you don't get to see that," Gledhill told Business Insider. "Typically what you see is a fixed pattern or a changing pattern based on the frequencies you play through the liquid."

Here's a look at some of Gledhill's newest experimental and hallucinatory imagery.

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Gledhill started experimenting with standard macro-photography camera gear. He took images of a roughly one-inch-wide, quarter-inch-deep dish of water vibrated by a speaker.

The camera peers down on the dish through a an LED light ring, which evenly illuminates the liquid in the dish. (In this case, malt whiskey.) The light ring is visible in a reflection at the center of this image.

Here's a photo of Gledhill's cymascope rig at his home.

• Having your shower curtain stick to you can be a pesky nuisance.
• The reason behind this annoying phenomenon is the "Bernoulli Effect".
• The physics behind this effect also explains, in part, how airplanes stay airborne.

What these temperatures call for is a nice, refreshing shower — if only it weren't for that pesky shower curtain closing in and clinging to you the moment you hop in and switch on the water. Why does this happen?

The answer to that question lies in physics.

"Since a shower curtain is large yet light, it reacts to a small vacuum created in the shower cabin," Ohle Claussen of the Max Planck Institute for Dynamics and Self-Organisation explained to Business Insider. At least two physical effects cause this when you shower.

The vacuum sucks the curtain into the shower cubicle.

You can easily create a similar vacuum yourself by taking a thin piece of paper or a receipt and holding it to your lower lip. If you blow hard now, the note will not be pressed down, but will raise. Andreas Baumer of Business Insider tried it, as you can see in the above photo.

What he experienced is called the Bernoulli effect, which is part of the reason why airplanes can fly. It was the mathematician Daniel Bernoulli who noted that, in a space where the flow velocity is higher than in its surrounding environment, the air pressure there is always lower compared with its surroundings.

So if you blow over the paper strip, the speed of the air there is higher than under the paper, because the air below is, at most, moving only very slightly. This reduces the pressure of the air above the paper, creating a vacuum that sucks the sheet upwards. Your "over-friendly" shower curtain can also be attributed to this phenomenon.

Air from outside flows in and a pressure drop occurs

"When air enters the area of higher flow velocity, it must be accelerated in order to adapt to this velocity," Claussen explained. "In fluid mechanics, such an acceleration is combined with a pressure drop as the driving force. The additional kinetic energy the air particles receive is as a result of the fact that the higher air pressure in the area of slow flow works on these air particles when they reach the area of faster flow".

So pressure and speed are always connected where air flow is involved. The place of highest speed is also always the place of lowest pressure. "So if your shower head emits water at high speed in the shower cabin, the air in the cabin is carried away," says Claussen. "Consequently, air must flow in from the outside and be accelerated, resulting in a drop in pressure."

David Schmidt, a scientist from Massachusetts, highlighted a second cause for the negative pressure, using a computer that simulated the movement of water droplets. It showed that splitting water droplets in the lower part of the shower create a vortex that also contributes to negative air pressure.

So how do you stop your shower curtain sticking to you?

This effect is almost as great as the Bernoulli effect, according to Claussen. And the discovery was only made in 2001. This shows how small the occurring forces are but as the shower curtain is simultaneously large and light, it can be carried away by even the slightest dip in pressure.

The closer the air brings the curtain to the person in the shower, the more the Bernoulli effect is enhanced: "The same amount of air must now flow through a smaller gap and must therefore flow even faster in that small area. This increases the negative pressure at the point of approach until contact occurs.

The real question is: what can you do to put a stop to your overly affectionate shower curtain's embrace? Try attaching some weights to the curtain's base, inserting a lead tape through the hem, sticking the curtain to the tub with water or avoiding pulling it across so it's taut when you shower!

SEE ALSO: Your blood is actually never blue — here's why it's always red

Join the conversation about this story »

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Inhaling helium and talking like Daffy Duck is a classic party trick. But not many know how helium works. Helium is much lighter than air, so sound waves move much faster through the gas. This amplifies the higher frequencies in your voice. The gas sulfur hexafluoride works in the opposite way. The following is a transcript of the video.

It’s a classic party trick- suck down a balloon and you’ll sound like Daffy Duck every time. But helium isn’t the only gas that’ll change the way you talk. So what’s going on here?

Your voice is as unique as your fingerprint. Janice didn’t inhale a balloon full of helium. That’s just her “normal” voice. So, let's take a look at how that's even possible. The sound of your voice starts in your voice box, or larynx. It’s a two-inch piece of cartilage at the top of your throat. In the box are two stretchy strands of tissue, your vocal cords. Which vibrate against each other at a specific frequency when you talk.

Women generally have thinner, shorter, tighter vocal cords than men. So, their vocal cords vibrate faster which generates a higher pitched voice. That sound is called the fundamental frequency of your voice. On its own it just sounds like a simple buzzing. But when it reaches your vocal tract, the sound waves start bouncing around. Those reflections interfere with each other. Which creates a mix of other frequencies, that you can detect with a spectrogram. So even though your voice starts out as one frequency, it ends up as a mix of multiple ones.

And that's where helium comes into play. Helium is lighter than air. Which means sound moves faster through helium than through air – nearly 3 times faster, in fact. So the sound waves bounce around faster in your vocal tract, which amplifies the higher frequencies in your voice. It's sort of like how speeding up your voice makes it sound higher.

But hold on a sec. These people aren't inhaling helium. They're sucking down sulfur hexafluoride, which is six times heavier than air. So sound waves move slower through it, which amplifies the lower frequencies in your voice. But here's the fascinating thing. The pitch of your voice hasn't changed when you inhale either gas, because your vocal cords move at the same rate no matter what gas you're breathing. So your fundamental frequency stays, well fundamental.

Regardless of whether you want to sound like Daffy Duck or James Earl Jones, keep in mind that inhaling anything but air can be dangerous. Especially when the gas is denser than air, because it will sink to the bottom of your lungs. And you may have to get it out like this. What questions do you have about the human body? Let us know in the comments and thanks for watching.

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• A total lunar eclipse, or blood moon, will happen overnight on July 27.
• The eclipse will be colored orange-red due to sunlight passing through Earth's atmosphere and bouncing off the moon.
• The eclipse is slated to last nearly 1 hour 43 minutes — the longest in about a century.
• North America won't see the eclipse, since the moon will be below the horizon, but anyone can watch via a live video webcast.

Huge swaths of Earth are in for a special astronomical treat in late July: the longest total lunar eclipse in roughly 100 years.

During the evening of July 27 and into the early morning of July 28, Earth will pass between the sun and the moon to cast a shadow on our 4.5-billion-year-old satellite.

Earth's shadow isn't a dull gray, though.

It ranges from orange to an eerie blood-red hue if you're right in the middle, which is precisely where the moon will be this time around.

Here's that works.

How a total lunar eclipse colors the moon red

A total lunar eclipse and a total solar eclipse are similar, if not the reverse of one another, but their appearances are significantly different.

During a solar eclipse, the moon passes between Earth and the sun to cast its shadow on our planet. The shadow is colorless because the moon has no atmosphere to scatter or refract any sunlight.

Earth, of course, is a different story.

Our planet's nitrogen-rich atmosphere takes white sunlight, a mix of all colors of the spectrum, and scatters around the blue colors. This makes the sky appear blue during the day and the sun yellow.

Around sunset and sunrise, the light reaching our eyes has been more throughly scattered, so much that blues are nearly absent. This makes the sun and its light appear more orange or even red.

Roughly 240,000 miles away at the moon, the Earth would look quite stunning as the same air, like a big lens, refracts that tinged light toward the full moon.

"If you were standing on the moon's surface during a lunar eclipse, you would see the sun setting and rising behind the Earth,"David Diner, a planetary scientist at NASA's Jet Propulsion Laboratory, wrote in a blog post. "You'd observe the refracted and scattered solar rays as they pass through the atmosphere surrounding our planet."

This is why lunar eclipses are orange-red: All of that colored light is focused on the moon in a cone-shaped shadow called the umbra.

The moon is also covered in ultra-fine, glass-like rock dust called regolith, which has a special property called "backscatter." This bounces a lot of light back the same way it came from, in this case toward Earth (Backscattering also explains why full moons are far brighter than during other lunar phase.)

So, when we're looking at the moon during a total lunar eclipse, we're seeing Earth's refracted sunset-sunrise light being bounced right back at us.

The red color is never quite the same from one lunar eclipse to the next due to natural and human activities that affect Earth's atmosphere.

"Pollution and dust in the lower atmosphere tends to subdue the color of the rising or setting sun, whereas fine smoke particles or tiny aerosols lofted to high altitudes during a major volcanic eruption can deepen the color to an intense shade of red," Diner said.

This total lunar eclipse will also happen during what's called a "micro" moon, or the opposite of a super moon. This happens because the moon's orbit isn't perfectly circular, so it appears larger at times and smaller at others during its roughly 29-day-long orbit around Earth. (In this case it will look a bit smaller.)

Where and when to see the total lunar eclipse

North America will be out of luck this year, since the moon will be below the horizon. You can still watch on a live webcast, though, if you're located there.

But if the weather cooperates, most of eastern Africa, the Middle East, and central Asia should see the full and total lunar eclipse. Scientists in Antarctica should also have a great view.

Europe, eastern Asia, Australia, Indonesia, and other regions will enjoy a partial lunar eclipse, where the moon passes partly through Earth's shadow.

The partial eclipse begins when the moon first touches the penumbra or outer shadow of Earth. According to NASA, that should happen at 17:14 Universal Time on July 27.

The total eclipse — when the moon is fully inside the red-hued umbra of Earth — starts at 19:30 UT and ends at 21:13 UT. That's a full 1 hour 43 minutes, which is just four minutes shy of the longest total lunar eclipse possible, according to EarthSky.

The partial eclipse will resume immediately afterward, as the moon passes out of Earth's shadow, and the whole event will be over at 23:28 UT (early on July 28, depending on where you live).

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NOW WATCH: This NASA animation shows what this month's stunning lunar eclipse would look like on the moon

• The longest total lunar eclipse or blood moon in a century will happen overnight on July 27.
• From the moon, Earth will look like it's surrounded by a ring of fire — with its sunset and sunrise connected in a loop.
• NASA has an animation showing what Earth's glowing red ring might look like during a total lunar eclipse.
• North America won't see the eclipse, but anyone can watch via a live video webcast.

A total lunar eclipse happens when Earth slips in front of the sun to cast a ruddy-orange to deep-red shadow on the moon.

This is why the astronomical event is often called a blood moon. People in Earth's Eastern Hemisphere can see the longest lunar eclipse of the 21st century starting at 19:30 Universal Time (UT) on Friday, July 27.

However, imagine you're an astronaut who happens to be on the surface of the moon during a total lunar eclipse, and you look back home. What would you see?

NASA's Science Visualization Studio has illustrated the answer to this question with an animated video.

To someone on the moon during a lunar eclipse, the Earth would appear to be surrounded by a bright-red ring of fire.

The image above is taken from NASA's animation, which actually illustrates the precise appearance of Earth and the moon during the total lunar eclipse that occurred September 27, 2015.

But apart from the position of Earth's continents, this week's lunar eclipse will appear more or less the same from the moon's perspective.

Here's why.

What gives total lunar eclipses an orange-red color

Total lunar eclipses and total solar eclipses are essentially the reverse of one another.

However, their appearances are very different (whether you're observing them from Earth or its natural satellite).

During a total solar eclipse, the moon passes between Earth and the sun, casting a small, dark shadow on our planet. For those watching on Earth, the ring of the sun's light surrounding the moon looks colorless because the moon has no atmosphere. (Atmospheres, similar to glass lenses, can refract sunlight.)

Earth is surrounded by a blanket of air, though, and this lens-like refraction is ultimately why lunar eclipses make the moon look orange-red.

By volume, about 80% of Earth's atmosphere is made of nitrogen gas, or N₂, and most of the rest is oxygen gas, or O₂. Together, these gases take white sunlight — a mix of all colors of the spectrum — and scatter around blue and purple colors. Human eyes are much more sensitive to blues than purples, which is why the sky looks blue and the sun yellow to us during daylight hours.

During a sunset or sunrise, sunlight reaching our eyes has passed through a lot more atmospheric gas, and this effectively filters out the blues and makes the light appear orange or even red.

A similar thing happens during a lunar eclipse. Earth's atmosphere bends and focuses the sun's light into a glowing, cone-shaped shadow called the umbra.

The red color is never quite the same from one lunar eclipse to the next due to natural and human activities that affect Earth's atmosphere.

"Pollution and dust in the lower atmosphere tends to subdue the color of the rising or setting sun, whereas fine smoke particles or tiny aerosols lofted to high altitudes during a major volcanic eruption can deepen the color to an intense shade of red,"David Diner, a planetary scientist at NASA's Jet Propulsion Laboratory, wrote in a blog post in 2010.

What Earth looks from the moon during a total lunar eclipse

Roughly 240,000 miles away at the moon, the Earth would look quite stunning during a lunar eclipse.

"If you were standing on the moon's surface during a lunar eclipse, you would see the sun setting and rising behind the Earth," Diner wrote. "You'd observe the refracted and scattered solar rays as they pass through the atmosphere surrounding our planet."

On the moon, you'd see the sunrise and sunset of Earth connected together in a roughly 25,000-mile loop. And on the ground around you, normally drab-gray lunar dust, or regolith, would look a bit orange-red.

Earth's color-tinted umbra is always out there — if you had enough cash and a spaceship, you could fly into it anytime you wanted.

However, the moon's slightly tilted orbit means that it only passes through our planet's shadow only about twice every 11 months.

Where and when to see Friday's total lunar eclipse

The coming eclipse will happen during what's called a "micro" moon– the opposite of a super moon. This happens because the moon's orbit isn't perfectly circular, so it appears larger at times and smaller at others during its roughly 29-day-long orbit around Earth. In this case, it will look a bit smaller.

North America will be out of luck during the lunar eclipse, since the moon will be below the horizon. You can still watch the phenomenon on a live webcast, though.

If the weather cooperates, most of eastern Africa, the Middle East, and central Asia should see the full and total lunar eclipse. Scientists in Antarctica should also have a great view.

Europe, eastern Asia, Australia, Indonesia, and other regions will enjoy a partial lunar eclipse, where the moon passes partly through Earth's shadow.

The partial eclipse begins when the moon first touches the penumbra, or outer shadow, of Earth. According to NASA, that should happen at 17:14 Universal Time on July 27.

The total eclipse — when the moon is fully inside the red-hued umbra of Earth — starts at 19:30 UT and ends at 21:13 UT. That's a full 1 hour 43 minutes, which is just four minutes shy of the longest total lunar eclipse possible, according to EarthSky.

The partial eclipse will resume immediately afterward, as the moon starts to leave Earth's shadow. The whole event will be over at 23:28 UT (which might technically be early on July 28, depending on where you live).

See NASA's animation below of a total lunar eclipse from the moon.

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This Sunday, July 29, 2018, marks the 60th anniversary of NASA's establishment as a US government agency, when President Dwight D. Eisenhower signed the 1958 National Aeronautics and Space Act, its founding legislation.

Nearly two decades later, NASA was already envisioning what post-Earth communities in space could look like.

In the 1970s, physicists from Princeton University, the NASA Ames Research Center, and Stanford University created fantastical illustrations of massive orbiting cities for life after Earth. The scientists imagined a worse-case scenario in which our planet would be destroyed, and humankind would move to space.

Take a look at these designs, unearthed by The Public Domain Review.

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In the '70s, the scientists expected that people could travel to the first space colony by 2060. They designed three types that would orbit the sun.

The first design is this donut-shaped spaceship that would house about 10,000 people.

The city would be full of homes, shrubbery, and sidewalks. A river would flow through the center of the half-mile-wide ship.

• NASA plans to launch a robot on Saturday that will fly closer to the sun than any mission in history.
• The Parker Solar Probe will use a high-tech heat shield to avoid being destroyed.
• The probe is designed in part to study the sun's ultra-hot outer atmosphere, called the corona, among other mysteries.
• The mission may help scientists predict space weather events that can wreak havoc on Earth.

NASA is about to launch a $1.5 billion space mission to "touch" the sun and study its atmosphere, solar wind, and other mysteries.

The Parker Solar Probe (PSP) is scheduled to launch on Saturday, August 11, though it may launch as late as August 23. When it blasts off into space from Cape Canaveral, Florida, it will ride atop a powerful Delta 4 Heavy rocket built by United Launch Alliance.

PSP is designed to survive sunlight 3,000 times more intense than occurs at Earth and plow through a "solar wind" of high-energy particles that can get as hot as several thousand degrees.

Its mission is to crack two 60-year-old mysteries: why the sun has a solar wind at all, and how the corona — the star's outer atmosphere — can heat up to millions of degrees.

"That defies the laws of nature. It's like water rolling uphill," Nicola Fox, a solar physicist at the Johns Hopkins University Applied Physics Laboratory, said during a NASA briefing in 2017.

"Until you actually go there and touch the sun, you can't answer these questions," said Fox, who's a project scientist for the new mission.

If the robot pulls off all the science that NASA and its partners hope, it might also help researchers learn critical information about solar outbursts that can overload power grids, cripple satellites, disrupt electronics, and inflict trillions of dollars' worth of damage in a matter of hours.

How to 'touch' the sun 24 times — and survive

Scientists plan to fly the Parker Solar Probe by our sun about 24 times. During the PSP's closest approach, it will come within 3.9 million miles of the star.

That distance is about four times the width of the sun itself, nearly 24 times closer than Earth is to the star, and seven times nearer than any spacecraft has ever dared travel to the sun. This dangerous proximity will enable PSP to record unprecedented measurements of the sun's corona, solar wind, magnetism, and other properties.

Pulling these flybys off isn't straightforward. To put PSP on the correct path, NASA will zoom its probe past Venus seven times, which will help it reach speeds of more than 425,000 mph when it moves through the sun's corona. At that speed, you could travel from New York City to Tokyo in a minute.

The idea to do a mission like PSP started nearly 60 years ago. But temperatures reach about 2,500 degrees at the proximity scientists wanted to send a probe, so "the materials didn't exist" to make it happen, Fox said.

That changed recently with the development of a state-of-the-art, lightweight carbon composite. Engineers have crafted that material into a 4.5-inch-thick "ram" for the probe that will face the sun, absorb and deflect solar radiation, and protect a suite of gadgets behind it.

"Solar probe is going to be the hottest, fastest, and — as I like to call it — the coolest mission under the sun," Fox said.

Unraveling the mysteries of solar wind

Orbiting a star as close as Earth does means we live inside its atmosphere: a sea of moving particles, or solar wind, spews outward at about 1 million mph and bombards planets like ours.

Eugene Parker, an 89-year-old scientist after whom the probe was named, first discovered this solar wind in the mid-1950s. An editor of a science journal famously rejected his seminal paper in 1958 and scolded Parker — who was later found to be correct — for submitting it.

During the NASA briefing last year, Parker said he jokingly thought in 1958 that the editor "didn't have any real critique, so it must have been a really good paper." 

Since then, physicists have wondered what, exactly, accelerates this stream of particles to breakneck speeds. They also question how the sun's atmosphere can jump from thousands of degrees Fahrenheit to millions of degrees in a tight region just above the star's surface.

"We want to go down there, take the challenge of going into the worst environment in the solar system and … really prove what the processes are that, in fact, make and accelerate the solar wind," Thomas Zurbuchen, the associate administrator of NASA's Science Mission Directorate, said last year.

Protecting Earth from violent solar outbursts

Earth's magnetic field and atmosphere typically protect us from the solar wind.

However, the surface of the sun occasionally flings giant blobs of solar particles at us in events called solar storms or coronal mass ejections. This triggers the beautiful auroras at our planet's poles, but can also temporarily disturb Earth's magnetic field, which can in turn disturb electrical systems of all kinds.

While figuring out how to protect Earth isn't the main goal of PSP, researchers hope the mission equips heliophysicists (scientists who study the sun) with new information that can help them predict, characterize, and prepare the world for a potentially crushing solar blow.

"Until we can explain what is going on up close to the sun, we will not be able to accurately predict space weather effects that can cause havoc at Earth," states the mission's website.

Last year, NASA finished assembling the probe and put it through a brutal testing program (including sizzling-hot thermal exposure). It's now inside the Delta 4 Heavy rocket's fairing, or nosecone, and awaiting launch.

If all goes well after its launch, PSP should make its first pass of the sun in late 2018 and its final one in mid-2025.

This story was updated with new information. It was originally published on June 1, 2017.

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• A liquid is traditionally defined as a material that adapts its shape to fit a container, and under certain conditions, cats seem to fit this definition.
• Reformulating the question "are cats liquid?" illustrates some problems at the heart of rheology, the study of the deformations and flows of matter.
• My study on the rheology of cats won the 2017 Ig Nobel Prize in Physics.
• The prizes are awarded every year by Improbable Research, an organization devoted to science and humor.

A liquid is traditionally defined as a material that adapts its shape to fit a container. Yet under certain conditions, cats seem to fit this definition.

This somewhat paradoxical observation emerged on the web a few years ago and joined the long list of internet memes involving our feline friends. When I first saw this question it made me laugh, and then think. I decided to reformulate it to illustrate some problems at the heart of rheology, the study of the deformations and flows of matter. My study on the rheology of cats won the 2017 Ig Nobel Prize in Physics.

The prizes are awarded every year by Improbable Research, an organization devoted to science and humor. The goal is to highlight scientific studies that first make people laugh, then think. A ceremony is held every year at Harvard University.

What is a liquid?

At the center of the definition of a liquid is an action: A material must be able to modify its form to fit within a container. The action must also have a characteristic duration. In rheology this is called the relaxation time. Determining if something is liquid depends on whether it's observed over a time period that's shorter or longer than the relaxation time.

If we take cats as our example, the fact is that they can adapt their shape to their container if we give them enough time. Cats are thus liquid if we give them the time to become liquid. In rheology, the state of a material is not really a fixed property — what must be measured is the relaxation time. What is its value and on what does it depend? For example, does the relaxation time of a cat vary with its age? (In rheology we speak of thixotropy)

Could the type of container be a factor? (In rheology this is studied in "wetting" problems.) Or does it vary with the cat's degree of stress? (One speaks of "shear thickening" if the relaxation time increases with stress, or "shear thinning" if the opposite is true.) Of course, we mean stress in the mechanical sense rather than emotional, but the two meanings may overlap in some cases.

The 'Deborah number' and the flow of mountains

What cats show clearly is that determining the state of a material requires comparing two time periods: the relaxation time and the experimental time, which is the time elapsed since the onset of deformation initiated by the container. For instance, it may be the time elapsed since the cat stepped into a sink. Conventionally, one divides the relaxation time by the experimental time, and if the result is more than 1, the material is relatively solid; if the result is lower than 1, the material is relatively liquid.

This is referred to as the Deborah number, after the biblical priestess who remarked that on geological time scales ("before God") even mountains flowed. On shorter time scales one can see glaciers progressively flowing down valleys.

Even if the relaxation time is very large (days, years), the behavior can be that of a liquid if the Deborah number is small (compared to 1). Conversely, even if the relaxation time is very small (milliseconds), the behavior can be that of a solid if the Deborah number is large (compared to 1). This is the case if one observes a water balloon at the instant when it's popped.

The Deborah number is an example of dimensionless number: Since we divide one time period by another, the ratio does not have any unit. In rheology, and in science more generally, there are many dimensionless numbers that can be used to determine the state or regime of a material or system.

Measuring the speed of cake batter

For liquids there is another dimensionless number that can be used to estimate whether the flow will be turbulent, with vortices, or whether it will calmly follow the outline of the container (we say that the flow is laminar).

If the flow speed is V and the container has a typical size h perpendicular to the flow, then we can define the velocity gradient V/h. The inverse of this velocity gradient scales as a time.

Comparing this duration and the relaxation time produces the Reynolds number in the case of fluids dominated by inertia (like water), or the Weissenberg number for those dominated by elasticity (like cake batter). If these dimensionless numbers are large in comparison to 1, then the flow is likely to be turbulent. If they're small in comparison to 1 the flow is likely to be laminar.

Asking the question of whether cats were a liquid allowed me to illustrate the use of these dimensionless numbers in rheology. I hope that it will make people laugh and then think.

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• Astronauts on each of NASA's six Apollo missions planted an American flag on the moon.
• Powerful sunlight and a lack of atmosphere to filter it have likely bleached all of the Apollo flags white.
• As NASA celebrates its 60th anniversary on Monday, it's possible some of the flags are also disintegrating.

The photos have stood the test of time: A spacesuit-clad Apollo astronaut stands proudly next to a red-white-and-blue American flag on the moon, his national trophy telling the lonely world, "the United States was here."

Unfortunately, all six flags planted from 1969 through 1972 haven't fared so well. Images taken by NASA's Lunar Reconnaissance Orbiter in 2012 do show that at least five out six flags still stand. However, scientists think decades' worth of brilliant sunlight have bleached out their emblematic colors.

The result? The flags are probably completely bone-white by now, as we first learned from Gizmodo.

But their condition may now be even worse than that as NASA celebrates its 60th birthday on October 1: Some of the flags are likely starting to disintegrate.

Each one of the flags was made by the company Annin Flagmakers, woven out of rayon, and cost NASA $5.50 (more than $32.00 when adjusted for inflation). On the surface of Earth, such flags fade in sunlight. That's because ultraviolet light — the same wavelength that causes sunburn — isn't fully absorbed by our planet's atmosphere, and it excels at breaking down fibers and colors.

The moon doesn't have any atmosphere to absorb sunlight, and outside of craters there is no shade. This means the flags planted by the Apollo astronauts are exposed to constant, gleaming sunlight and even more solar radiation, and for two-week stretches at a time. (One "day" on the moon lasts about 28 Earth days.)

Writing in a July 2011 article for Smithsonian Air & Space magazine, lunar scientist Paul Spudis explains:

"Over the course of the Apollo program, our astronauts deployed six American flags on the Moon. For forty-odd years, the flags have been exposed to the full fury of the Moon's environment – alternating 14 days of searing sunlight and 100° C heat with 14 days of numbing-cold -150° C darkness. But even more damaging is the intense ultraviolet (UV) radiation from the pure unfiltered sunlight on the cloth (modal) from which the Apollo flags were made. Even on Earth, the colors of a cloth flag flown in bright sunlight for many years will eventually fade and need to be replaced. So it is likely that these symbols of American achievement have been rendered blank, bleached white by the UV radiation of unfiltered sunlight on the lunar surface. Some of them may even have begun to physically disintegrate under the intense flux.

"America is left with no discernible space program while the Moon above us no longer flies a visible U.S. flag. How ironic."

Will we return to the moon?

Much has changed — and a lot hasn't — since Spudis' lament.

No person has returned to the moon.

However, NASA is working hard to fly astronauts into deep space by developing its ultra-powerful Space Launch System rockets. The goal is to build a "gateway" that'd reach lunar orbit around 2026, according to NASA's latest plans.

The lunar space station could be then filled with astronauts. From there, the astronauts could control lunar landers and robots (perhaps to scout for water deposits that could be mined and turned into rocket fuel) and eventually use the facility as a way point to send people to and from the surface.

The commercial sector is also working on grand plans to reach the moon.

Tech mogul Elon Musk and his aerospace company, SpaceX, are building a giant carbon-fiber spacecraft called Big Falcon Rocket that should be capable of reaching the moon or Mars. By 2023, Musk plans to launch the company's first space tourist — a Japanese billionaire named Yusaku Maezawa— in one of the spaceships, along with a crew of hand-picked artists. The plan is to fly them around (but not land on) the moon.

Amazon founder Jeff Bezos, who owns the rocket company Blue Origin, is eager to move industry into space and colonize the moon.

Yet prior to these larger companies reaching the moon or landing any people there, smaller outfits like SpaceIL may land a robot on the surface as soon as 2019. They would not only deliver small private payloads, but also broadcast high-definition footage of their adventures back to Earth.

Other companies with similar robotic plans may try to land near the site of Apollo 11, 12, 14, 15, 16, or 17 and record live views of the historic sites as they look today.

If that comes to pass, there may be an iconic flag in the frame — and we might settle the question of what they actually look like after spending more than 45 years under the sun.

Jennifer Welsh contributed reporting to a previous version of this article.

This story has been updated with new information. It was originally published on April 9, 2017.

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• Dr. Donna Strickland jointly won the Nobel Prize for Physics on Tuesday, but she did not have a Wikipedia page until then.
• As recently as May, a Wikipedia entry for Strickland was rejected as it failed to "show significant coverage" of Strickland's work.
• Strickland won the 2018 prize for breakthroughs in the field of lasers, becoming the third woman to receive the honor in physics. 

 Nobel Prize-winning scientist Dr. Donna Strickland did not have a Wikipedia page until she became a Nobel laureate, and earlier attempts to write a page for her were rejected because she was not famous enough.

Strickland won the 2018 Nobel Prize for Physics for breakthroughs in the field of lasers on Tuesday alongside French scientist Gerard Mourou. The pair were awarded the prize jointly, and the Royal Swedish Academy of Sciences said their inventions "have revolutionized laser physics."

But a Wikipedia page was only successfully created for her after she won. As recently as May, a Wikipedia entry for Strickland was rejected as it failed to "show significant coverage (not just passing mentions) about the subject."

As Quartz noted, prior to winning the Nobel Prize, Strickland’s only previous mention on Wikipedia was in an article about Mourou.

Strickland is the third woman to win the Nobel Prize in Physics, and is the only living female winner.

At a press conference on Tuesday, Strickland was surprised to learn she was the third woman to receive the honor in physics. "Is that all, really? I thought there might have been more," she said. "We need to celebrate women physicists because we’re out there. Hopefully, in time, it will start to move forward at a faster rate."

Strickland is an associate professor of physics at the University of Waterloo in Canada, and many have noted that her academic rank does not appear to reflect the significance of her work.

Strickland told the Globe and Mail that the explanation is a matter of priorities. She has never sought the higher title, which requires a candidate to spend time gathering support.

Strickland now has a Wikipedia page, which describes her as "a Canadian physicist, academic, and Nobel laureate, who is a pioneer in the field of lasers."

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• The 2018 Nobel Prize in physics was awarded to scientists who developed tools made from light beams.
• One half of the prize went to Arthur Ashkin for his work on optical tweezers, which are beams of light that can manipulate tiny objects like cells or atoms.
• The other half went to Gérard Mourou and Donna Strickland for creating technology that generates high-intensity laser pulses, which are used in everything from eye surgeries to plasma physics.

Our world is full of light, and we depend upon it to power life on our planet. So it is appropriate to honor three scientists who invented new ways of using light rays to explore our world.

The 2018 Nobel Prize in physics was awarded to Arthur Ashkin, Gérard Mourou, and Donna Strickland for developing tools made from light beams. Ashkin won half of the prize for his work on optical tweezers, which are beams of light that can actually manipulate tiny objects like cells or atoms, while Mourou and Strickland won the other half for creating technology that generates high-intensity, ultra-short laser pulses, which are used for eye surgeries, material sciences, studies of very fast processes, and plasma physics, among others.

Alfred Nobel specified in his will that the physics prize should be awarded for "the most important discovery or invention within the field of physics," so as a physicist I think he'd be pleased that this year's award recognizes inventions made in the 1970s and 1980s that have led to practical applications that benefit mankind.

Donna Strickland is only the third woman to win the Nobel Prize in physics, out of 210 recipients, and the first since 1963. Marie Curie was the first, in 1903; she won another one in 1911 for chemistry. Maria Goeppert-Mayer was the second. Hopefully in the future the Nobel Prize committee can lower the average of 60 years between women laureates being named.

What are optical tweezers?

Using light to manipulate our world has become very important in science and medicine over the past several decades. This year's physics Nobel recognizes the invention of tools that have facilitated advances in many fields.

Optical tweezers use light to hold tiny objects in place or measure their movement. It may seem odd that light can actually hold something in place, but it has been well-known for more than a century that light can apply a force on physical objects through what is known as radiation pressure.

In 1969, Arthur Ashkin used lasers to trap and accelerate micron sized objects such as tiny spheres and water droplets. This led to the invention of optical tweezers that use two or more focused laser beams aimed in opposite directions to attract a target particle or cell toward the center of the beams and hold it in place. Each time the particle moves away from the center, it encounters a force pushing it back toward the center.

Steven Chu, Claude Cohen-Tannoudji and William D. Phillips won the 1997 Nobel Prize in physics for development of laser cooling traps, known as optical traps, that hold atoms within a confined space. Askhin and Chu worked together at Bell Laboratories in the 1980s laying the foundation for work on optical traps.

While Chu continued work with neutral atoms, Ashkin pursued larger, biological targets. In 1987, Ashkin used optical tweezers to examine an individual bacterium — without harming the microbe. Now optical tweezers are routinely used in studies of molecules and cells.

Ashkin earned his bachelor's degree from Columbia University and his Ph.D. from Cornell. He started at Bell Laboratories in 1952 and retired in 1992. But he assembled a home laboratory to continue his scientific investigations. He has been awarded more than 45 patents.

Why are fast laser pulses important?

Gerard Mourou and Donna Strickland worked together at the University of Rochester, where they developed the technique called chirped pulse amplification for laser light. Strickland was a graduate student and Mourou was her thesis advisor in the mid-1980s.

At the time, progress on creating brighter lasers had slowed. Stronger lasers tended to damage themselves. Strickland and Mourou invented a way to create more intense light, but in short pulses.

You are probably most familiar with laser pointers or barcode scanners, which are just some of the ways we use lasers in everyday life. But these are relatively low-intensity lasers. Many scientific applications need much stronger ones.

To solve this problem, Mourou and Strickland used lasers with very short (ultrashort) pulses — quick bursts of light separated in time. With chirped pulse amplification, the pulses are stretched in time, making them longer and less intense, and then the pulses are amplified up to a million times.

When these pulses are compressed again (through reversing the process used to stretch), the pulses are much more intense than can be created without the chirped pulse amplification technique. As an analogy, consider a thick rubber band. When the band is stretched, the rubber becomes thinner. When it is released, it returns to its original thickness. Now imagine that there is a way to make the stretched rubber band thicker. When the band is released, it will end up thicker than than the original band. This is essentially what happens with the laser pulse.

There are a variety of ways the stretching and amplification can be done, but nearly all of the highest-power lasers in the world use some variation of this technique. Since the invention of chirped pulse amplification, the maximum intensity of new lasers has continued a dramatic rise.

In my own field of particle physics, chirped pulse amplification-based lasers are used to accelerate beams of particles, possibly providing a path to greater acceleration in a shorter distance. This could lead to lower-cost, high-energy accelerators that can push the bounds of particle physics — enabling us to detect evermore elusive particles and gain a better understanding of the universe.

But not all particle accelerators are behemoths like the Large Hadron Collider, which has a circumference of 17 miles. There are some 30,000 industrial particle accelerators worldwide that are used closer to home for material preparation, cancer treatment and medical research. Mourou and Strickland's work may be used to shrink the size of these accelerators making them smaller and cheaper.

Ultrafast, high-intensity lasers are also now being used in eye surgery. It can be used to treat the cornea (surface of the eye) to improve vision in some patients. The chirped pulse amplification invention is also used in attosecond science for studying ultrafast processes. An attosecond is one million trillionth of a second.

By having lasers that produce pulses every attosecond, we can get a snapshots of extremely fast processes such as atoms losing an electron (ionizing) and then recapturing it.

The Nobel Prize-winning work was the basis for Strickland's Ph.D. thesis from the University of Rochester. Dr. Strickland is now an associate professor at the University of Waterloo in Canada. Mourou became the founding director of the Center for Ultrafast Optical Science at the University of Michigan in 1990. He later became director of the Laboratorie d'Optique de Applique in France.

The 2018 Nobel Prize in physics shines a light on the pioneering work of these three scientists. Over the past three decades, their inventions have created avenues of science and medical treatments that were previously unattainable. It is certain that we will continue to benefit from their work for a long time.

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