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Ethan Siegel
Science writer, professor and theoretical astrophysicist
Science writer, professor and theoretical astrophysicist

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“When the ground’s brightness surpasses the sky’s, clouds appear bright against the night, rather than as dark silhouettes. While cameras reveal many more stars than the unaided eye can, a dark, night sky offers spectacular views to humanity. As urbanization increases, dark skies become rarer and less pristine.”

For all of human history, we’ve battled against the limitations of our bodies and the natural world. That’s led to the development of artificial lighting: from fire to modern electric and LED lights. Despite being able to see our surroundings much more clearly at all hours regardless of the Moon or the clouds, we’ve also lost something spectacular: the night skies themselves. There are thousands of stars visible to the naked eye from a truly dark-sky location, yet such places are increasingly harder to come by. East of the Mississippi in the United States, they barely exist at all. From many urban locations, even bright, easily recognizable sights like the North Star or the Big Dipper are no longer visible.

Come see what light pollution costs us every night, and learn why, if we don’t do something, the only place to get dark skies will be in space.

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"You’d need to strip off the H/He envelope early, and most of the rest of a “puffy” atmosphere as well. You’d need to strip the world down to only a thin atmosphere, but not beyond that. And then you’d need to have a planetary migration outwards occur, away from the star and out towards a more temperate zone. Certainly, this is possible, and pointing to the possibility of planetary migration in our own Solar System is a good example. You’d also want a star that was G-class or more massive, for the ultraviolet radiation providing a necessary “kick” to the atmospheric particles, but not too much more massive so that the lifetime of the star/planetary system was too short."

How can you make a super-Earth habitable? How does the Universe become reionized? How will James Webb tell us what we don't yet know, and how can we go beyond the first stars? How do the Big Bang and the expanding Universe work? And most importantly, how do we get correct information to people (and protect them from misinformation) in today's world?

Lots of answers, lots of questions and some things we can all think about on this edition of our Comments of the Week!

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“Sometimes (usually Fridays after work) my friend Scotty beams me up to USS Enterprise for a ride around Sun following the orbit of planet Earth. The warp takes about 2 hours, so I guess our speed is very close to light speed, but not quite. During the ride I usually have a couple of beers, so when Scotty beams be back to my front door, my wife has difficulties believing me when I tell her that I was not at the local Pub…”

So, your friend on the USS Enterprise beamed you aboard, took you on a relativistic journey at impulse speeds around the Solar System, and brought you back to your starting point. You find that less time has passed for you than your family who remained on Earth, yet you’ve traveled a much greater distance. How does this all work? How much energy does it take, what’s the science behind it, and how do you get your family to believe you when you tell them what happened to you? Some basic advice: give them times in their reference frame, admit to the drinking you actually do, and if you go someplace unbelievable, take a photo!

To find out even more, and learn about my upcoming new book, Treknology: The Science of Star Trek from Tricorders to Warp Drive, check out this week’s Ask Ethan!

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I wrote a book! It's called Treknology, and it's about the real-life science, up-to-date, about a huge slew of the technologies dreamed up by Star Trek. From warp drive to transporters to VISORs to human life extension to androids and more, you won't want to miss it.

Plus we've got the official license rights from CBS and Paramount, so images from your favorite Star Trek moments will be featured.

The book comes out October 15th, and this is the official announcement from Star Trek!

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“But there’s one killer move that stars have that makes carbon a loser in the cosmic equation: when a star is massive enough to initiate carbon fusion – a requirement for generating a type II supernova – the process that turns carbon into oxygen goes almost to full completion, creating significantly more oxygen than carbon by time the star is ready to explode.”

When the Universe was first born, all we had was hydrogen and helium, with a trace amount of lithium and absolutely nothing else. 13.8 billion years later, hydrogen is still #1 in the Universe and helium is still #2, but lithium isn’t close to #3 anymore: more than two dozen elements have passed it. The key? Stars! Over billions of years, nuclear fusion in the cores of stars have built up all the naturally occurring elements we know of in the periodic table. You might think that since three heliums can fuse together to make carbon, that would be the third most common element in the Universe. And it’s close: carbon comes in at #4. But another element has it beat.

Hydrogen's one, helium's two. Who's number three? This story's for you!

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“ What they find is that the transition from “rocky” world to “gaseous” world occurs at just twice the Earth’s mass. If you’re more that twice the mass of Earth and you receive the same amount of energy from your star, you’ll be able to hold onto a substantial hydrogen-and-helium envelope of gas, creating an atmospheric pressure that’s hundreds or even thousands of times as great as what we have on Earth’s surface. The hope that Super-Earth worlds would be Earth-like is shattered, and we can safely put Super-Earths, Mini-Neptunes and Neptune-like worlds into the same overall category. ”

It was quite a surprise when we started discovering all the exoplanets that were out there. While there’s a big gap between a world like Earth and a world like Uranus or Neptune in our Solar System – 17 times the mass and 4 times the radius – most of the worlds out there fall in between these two types. Super-Earths and Mini-Neptunes are the most common. But it turns out that what we’re calling a “Super-Earth” is a total misnomer! These worlds may be larger than Earth, but they’re much more like Uranus or Neptune than they are like our own. They have big gas envelopes surrounding them, and can even hold on to their young hydrogen and helium. The only way out is to boil the atmosphere away, and if you do, you’ve got a rocky core that’s close enough to its star to be roasted.

Come find out the full story behind why there’s no such thing as a habitable Super-Earth!

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"Would you fire a gun into the air in celebration if you knew that, when the bullet comes down, it could kill somebody? It's no surprise that bullets fired towards a target can easily destroy whatever they run into: a bullet from an AK-47 leaves the rifle traveling at over 1,500 miles per hour (670 meters per second): about double the speed of sound. Despite only having a mass of about five grams -- under a fifth of an ounce -- it's got the energy of a brick dropped from a 30 story building."

Bullets are incredibly dangerous when fired from a gun, but that's true even when they're fired up in the air, not at a target directly. Falling, stray bullets can still reach very large speeds, large enough to break the skin and cause internal damage, potentially even killing someone. There are huge variations in what can happen depending on the weight and size of the bullet, the angle it was fired at, your altitude, the thickness and elasticity of the skin it strikes and where it impacts you. The most dangerous times are New Years and 4th of July in urban areas, and there are numerous documented cases of injury and death resulting.

Don't be an innocent bystander, and don't be part of the problem. There are steps we can all take to be safe, so spread the word!

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"So how close could we actually get to a flat planet? One strategy would be to take a solid slab of material -- stone, steel, or something even harder like diamond or graphene -- and build the largest flat disk you could. If you used conventional materials like this, you could create a thin, flat disk many hundreds of kilometers in radius that was stable. In other words, you could make a flat world that was larger than any object in our asteroid belt, and possibly even nearly the size of our Moon."

We have some pretty good definitions of what it takes to be a planet, and one part of that definition is that a world needs to be massive enough to pull itself into hydrostatic equilibrium. In the absence of external forces and rotation, that means it will be a perfect sphere. But what about if you allow the other forces to come into play? In addition to the many interesting features you'll get, one of them is a flattening of your world. So that brings up the question of how flat a planet could possibly be? This isn't just theory; our own Solar System has a great example that you'll want to see for yourself!

The world may be very close to a perfect sphere, but not all worlds are. Come find out the science of why!

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“By warping space, the light from background objects gets magnified, revealing extraordinarily faint galaxies. The only problem? The cluster itself is closer and overwhelmingly luminous, making it impossible to tease out the distant signals. Until now. Thanks to a superior new technique devised by Rachael Livermore, light from the foreground cluster galaxies can be modeled and subtracted, revealing faint, distant galaxies never seen before.”

One of the biggest puzzles in science is exactly how the Universe became transparent to visible light. Neutral atoms – cosmic dust – blocks visible light, and yet before there were stars, that’s all we had. According to theory, it should be large numbers of small, faint, ultra-distant galaxies that made it transparent, but they’ve never been seen. However, thanks to the combined power of the Hubble Space Telescope, gravitational lensing and a new foreground light-removal technique, galaxies 100 times fainter thank the ones visible in the Hubble eXtreme Deep Field – the longest-exposure image ever – have now been revealed. These galaxies, seen in two Frontier Fields’ clusters so far, are the ‘missing link’ needed to explain reionization.

Come get the full, stunning story in visuals and no more than 200 words on today’s Mostly Mute Monday!

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“The total amount of information accessible to us in the Universe is finite, and hence, so is the amount of knowledge we can gain about it. There’s a limit to the amount of energy we can access, the particles we can observe and the measurements we can make. There’s a whole lot left to learn and a whole lot that science has yet to reveal, and many of the present unknowns will fall in the near future. But some things we will likely never know. The Universe may yet be infinite, but our knowledge of it never will be.”

There are lots of deep, wonderful questions to ask about the scientific ideas permeating the world. They range from gravitation to cosmology to black holes to galaxies to the birth of the Universe, and I do my best not to shy away from any of them. But science alone doesn’t tell us everything. There are limits to what we can know, scientifically. Don’t fall into the mistake of thinking that this means “anything is possible” and that “science is valueless,” though. Scientific knowledge -- real knowledge -- is valuable in a way nothing else is. And if you’re honest about what science actually knows, maybe you won’t be tempted to give into the alternative facts that suit your preferred beliefs.

Come get a big dose of reality, along with my view on rights and what God should (and shouldn’t) be, on this edition of our Comments of the Week!
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