A gorgeous view of M51 - the Whirlpool Galaxy

[BootinUp]

This image is a composite of many separate exposures made by the ACS instrument on the Hubble Space Telescope.

(Credit: NASA, ESA, S. Beckwith (STScI), and the Hubble Heritage Team - STScI/AURA)

[1WorldHope]

1. So do the colors represent chemicals or direction?

[Bernardo de La Paz]

2. Chemical compounds. They reflect differentially in bands of spectrum including infrared.

Actually, not mainly reflection for starlight, which is emission. There is also filtering by dust clouds and that tend to be the "redder" areas. The image probably includes some infrared emissions, which are better at getting through dust and gas and those are usually assigned very red colours.

If you are thinking of "red shift", that requires much higher velocities than galactic rotation (guessing 10,000 to 100,000 mph). Red shift is for objects going away from us (receding) at speeds a significant fraction of the speed of light. 36,000 mph is 10 miles per second. One percent (faint red shift) of the speed of light is 1,860 miles per second. So galactic motion does not produce visible red shift (possibly it might be detectable by careful examination of spectral lines, I don't know).

[1WorldHope]

4. Do you know what the chemical compounds would be by the color?

I love the study of space but I only know enough to ask stupid questions. My teachers would be Carl Sagan and Neil for Grasse Tyson.

[Bernardo de La Paz]

5. The only stupid questions are the ones not asked or ones asked as something other than questions.

You are not asking stupid questions.

Yes, the compounds could be detected by very careful fine grain analysis of multiple colour filtered images in principle. I'm not sure if images are the actual way, or if there is other multi-band spectral analysis of finer grained samples.

Different compounds glow at different colours dominated by spectral lines. Those are bright lines that are specific to certain electron orbital shifts. When an atom gets heated, its electrons get excited and shift to more energetic orbits. Then they re-emit some of that energy as they fall to lower energy orbits, energy mostly as photons of certain wavelengths (colours) depending on the exact orbitals.

Hydrogen for example has a very bright line. "21 cm" is what my faulty memory suggests, or maybe that might be a wavelength with very little emission from any element (specifics could be looked up but are not key to the principle of the emissions).

Dust clouds and outer layers of stars "atmospheres" can show as dark lines (absorption spectra).

It has to be all very carefully calibrated and analyzed, but that is what is what astronomers do.

[Deuxcents]

3. 🤩 It's mesmerizing

[Frasier Balzov]

6. There must be hundreds of stars!

[Lucky Luciano]

7. Just a single cell in a larger alien organism...

…I often make up stories to myself like that!

[lastlib]

8. "MY GOD! It's full of STARS!!....."