Always in Motion

This is an unaltered pic of the night sky, focused on the Hartley 2 comet in center. Pretty eh? 

We still use many anachronisms in our daily speech - sunrise and sunset, for example. Fact is, the sun's doing nothing of the sort, but rather our planet is spinning at approximately 26000MPH. When the Earth turns towards the sun, that's "sunrise".

So the Earth is spinning, but it's also moving, round and round the sun. But the Sun is moving too, round and round the center of the galaxy. And the Milky Way is moving too, round and round a shared gravitational center with Andromeda - and our local group of galaxies are moving round and round a shared gravitational center with another group of galaxies, and so on, forever.

Everything is in motion - including, at all times, every particle that makes you up.

All this motion means, there is no "absolute motion" - what would you judge it against? And thus, we have Einstein's relativity. Easy example: You're at the train station, and a train goes flying by. On the train, a boy is tossing a ball up and down. To you, the ball looks like it is arcing through the sky; to the boy, the ball is going straight up and down. One action, two completely different frames of motion, and thus it appears different to different observers. This is a powerful concept.

But not why I'm here. Rather, redshift (Redshirt cousin). Whether you know it or not, you're familiar with the Doppler Effect - an approaching police car with siren will sound higher pitch as it approaches you (because the sound waves are more compact, higher frequency), and then lower pitched as it pulls away, even though from the police car perspective, the sound never changed.

The same happens with light - light from a source heading towards us will appear bluer - shorter, more energetic wavelengths. Light from a source moving away from us will appear redder - longer, less energetic wavelengths. Turns out, almost everything is moving away from everything else, and thus the theory of the Big Bang (if everything's moving away from everything else right now, than it follows everything used to be closer together).

But that's also not why I'm here. Rather, witness the wonders of Spectroscopy!
 This pretty picture is the spectral analysis of visible light from the sun - you see the ever familiar rainbow, of course, but also, all those black lines. Those black lines represent elements - hydrogen, helium, lithium, carbon, etc. Thus, simply by analyzing light in this manner, you learn what the light-emitting object is composed of. Further, the location of each of these black lines is generally the same, and thus, if they appear at different locations in the spectrum, you can infer the object is moving away - thus, the actual definition of redshift is here - the chemical composition will all be shifted towards the red. 

And thus, you see how light is "scattered" as it hits our atmosphere, and encounters the gases within it - these black lines represent a "scattering" of sorts.

Finally, because of this interplay of electromagnetic wavelengths (remember, visible light is only one small piece of the overall electromagnetic spectrum) and the elements, we have the warm and welcoming world we live in today. Look!

 As you can see, only certain type of wavelengths can get through our atmosphere - and lucky for us, since if gamma rays could pass through, I doubt you'd be reading this. This is the exact same effect that causes our sky to be blue. In conclusion!

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