Light At Night

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GRB 090423: The Farthest Explosion Yet Measured

Credit: Gemini Observatory / NSF / AURA, D. Fox & A. Cucchiara (Penn State U.), and E. Berger (Harvard Univ.)

Explanation: An explosion so powerful it was seen clear across the visible universe was recorded in gamma-radiation by NASA’s orbiting Swift Observatory. Farther than any known galaxy, quasar, or optical supernova, the gamma-ray burst recorded was clocked at redshift 8.2, making it the farthest explosion of any type yet detected.

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Snake in the Dark

Credit & Copyright: Stéphane Guisard (Los Cielos de Chile) 

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Zodiacal Light Vs. Milky Way

Credit & Copyright: Daniel López, IAC 

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Bright Bolide

Credit & Copyright: Howard Edin (Oklahoma City Astronomy Club) 

fuckyeahspaceexploration:

Look closely and you’ll see two moving objects in this footage. The most obvious one is a meteor however, more subtly in the middle towards the top right, there’s a small object moving slowly up and that is a fuselage of a Russian rocket breaking up in the upper atmosphere.

(Source: nasa.gov)

pretendy:

Why is the night sky dark?

This is a question that at first sounds a bit stupid, but the observation that the night sky is dark is in fact a deeply profound one that provides much of the basis for modern cosmology.

The question which has now come to be known as Olbers’ paradox goes something like this: “In an infinite and static universe with an infinite amount of stars, why is the night sky dark?”

Why?

The argument was that if you looked at any point in the sky and drew your line of sight, it would eventually reach a star. In other words, along every possible direction, there should be a star, and hence light should be coming from every point in the sky.

No, really, why?

This is a bit of a wishy-washy argument when posed in terms of words, so let’s try some maths:

Imagine that throughout the universe, the density of stars (number per cubic lightyear, say), let’s call it n, remains roughly constant. Now, imagine that we construct a series of spherical shells surrounding the Earth, and that each has a thickness dr. See the main picture to see what I mean.

What we want to do is count up the number of stars, N, in a shell. For a shell a distance r away, we multiply its volume by the star density:

Now let’s work out how bright that shell is. We can assume that each star has a total luminosity of L, but we have to take into account the fact that the further away a star is the fainter it appears. In fact, the apparent brightness, F, of any star varies like:

The brightness of a thin shell - which we’ll call dJ- is just the number of stars times the brightness of each!

Now we integrate over all space, i.e., add up the contribution from every consecutive shell all the way to infinity.

In other words, the total brightness of the sky, J, is infinite!

Okay but WHY?

The essential reason for this is the fact we said that the brightness of a star decreased by an inverse square law, but the number of stars increased by a regular square law. The two r^2 terms cancelled each other out and we found that each shell had the same brightness! Therefore when you add up an infinite number of same-brightness shells the answer you get is ∞.

Oh. So?

Well, this is obviously not true when we look up at the sky, so there must be a problem somwhere. Like most things in science, the problem lies within our initial assumptions, namely: ‘the universe is static and infinite’. We have shown that this just can’t be true! The night sky being dark forces the universe to have a finite size and age!

Edgar Allen Poe was eerily accurate when he postulated that no light reaches Earth from beyond a certain distance - corresponding to the age of the oldest stars. Cosmology caught on to this idea and introduced the concepts of the big bang, universal expansion, and the cosmic horizon in order to account for this seemingly trivial darkness problem.

Think of this next time you look at a starry sky. We see faint objects as they were hundreds, thousands, millions and billions of years ago (the time it has taken light from them to reach our eyes). At the farthest depths of what our most powerful telescopes can make out are objects from the beginning of the universe itself, and beyond that… nothing.

We can see the edge. It’s black.

Cool.

Check out this horrific picture. Okay, okay, as a picture, it’s pretty neat, kind of surreal. Even I have to admit, I like it, but I am most definitely horrified by what’s going on here.

This picture was taken by Tom Anderson. Remember him? The guy who started MySpace. He took this photo in Taiwan and posted it to Facebook.

I was driving through the mountains of central Taiwan…up ahead in the distance, I spied a huge glow lighting up the night sky. This wasn’t a single light source, it looked more like a spaceship had landed…As I drove closer I started to get a sense for what was going on, and then I found what you see here in the picture. I’m not sure, but I’m guessing the lights are there to make the crops grow faster.

About thirty seconds of internet research found me this.

Tianwei in ChanghuaCounty is also known as the Garden of Taiwan. At night the flower farms on both sides of the highway are ablaze with light as the flower farmers simulate sunlight to encourage the growth of the flowers. The massive fields of shining lights in the night make for quite a spectacular sight.

I don’t know how Taiwan compares to China, but I’ve heard it’s near impossible, if not completely impossible, to see stars at all in and around China’s urban areas. I haven’t been able to find any really credible sources for this, but I’ve also heard this is not due solely to light pollution, but even air pollution. Well I don’t know about that, but looking at pictures like this, I can see how light pollution is a real epidemic in Asia.

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Zodiacal Light Panorama

Image Credit & Copyright: Miloslav Druckmüller (UM FSI, Brno Univ. of Technology), Shadia Habbal (IfA, Univ. of Hawaii)