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reptile
2003-Jun-01, 02:01 PM
Hi,

I'm doing an essay on Spectral Analysis at the moment (need it on
monday). I'm looking for a picture of a star or a galaxy (probably
from Hubble) with descriptions on what the colours on that picture
tell us about the chemical structure, the heat etc. of what we're
seeing - it shouldn't be too complicated though as i'm not an expert
at this anyway. Of course I'd prefer a beautiful picture if possible
:)

Anyone got something like that for me?

Crimson
2003-Jun-01, 03:15 PM
Hi,

I'm doing an essay on Spectral Analysis at the moment (need it on
monday). I'm looking for a picture of a star or a galaxy (probably
from Hubble) with descriptions on what the colours on that picture
tell us about the chemical structure, the heat etc. of what we're
seeing - it shouldn't be too complicated though as i'm not an expert
at this anyway. Of course I'd prefer a beautiful picture if possible
:)

Anyone got something like that for me?

OK, I'll keep it simple.

Ken Croswell's elegant book Magnificent Universe (http://www.amazon.com/exec/obidos/ASIN/0684845946) has a huge color portrait of the Dumbbell Nebula from the VLT (page 85) and also available here (http://www.eso.org/outreach/press-rel/pr-1998/phot-38-98.html) (but it looks better in the book). The green comes from oxygen, the red comes from hydrogen and nitrogen, and where the two colors mix they make yellow.

Pages 59 and onward of the book show a number of stunning images of H II images (H II = ionized hydrogen). Ionized hydrogen glows red, which is why objects like the Lagoon Nebula (page 59), the Trifid (page 60), etc., are red.

Strangely enough, however, BLUE stars are responsible for the red glow, since only the hottest stars generate the extreme ultraviolet light necessary to ionize hydrogen.

Sometimes, the blue light reflects off dust, so you also see blue--e.g., the bottom part of the Trifid Nebula on page 60. Where the red and blue mix they make purple (e.g., The Flaming Star Nebula, page 69 of the aforementioned book) or magenta.

And sometimes a blue star isn't hot enough to ionize hydrogen, in which case all you see is blue light reflected off dust. See page 68 of Magnificent Universe for a stunning image of the Witchhead Nebula--entirely blue--whose color arises from light from the blue supergiant Rigel (visible at the top of the image). Rigel is spectral type B8, which is too cool to ionize hydrogen.

reptile
2003-Jun-01, 03:19 PM
thanks a lot! Those two Dumbbell Pictures are perfectly alright for what I need :)

reptile
2003-Jun-01, 04:00 PM
oh but i have one more question:

when the astronomers do these pictures, they're not actually that colorful, right? All those colors are just there to represent the different wavelenghts, aren't they?

The Bad Astronomer
2003-Jun-01, 04:51 PM
Here is how the color pictures are made (http://opostaff.stsci.edu/~levay/process/). Also, this site may help as well (http://heritage.stsci.edu/commonpages/infoindex/ourimages/index.html).

reptile
2003-Jun-01, 05:08 PM
thanks!

reptile
2003-Jun-01, 08:51 PM
hm, excuse my ignorance, but i have one (hopefully) REALLY last question. When looking at diagrams of spectral analysis, what does the curve actually show? I mean, is it the intensity of the light on a specific wavelength? Or is it something else?

Just need to know what the "x" and "y" variables (so to speak) represent.. i've seen diagrams on which there was some text but it was more like the formula not something general like "intensity", which is all i need.

Donnie B.
2003-Jun-01, 11:13 PM
hm, excuse my ignorance, but i have one (hopefully) REALLY last question. When looking at diagrams of spectral analysis, what does the curve actually show? I mean, is it the intensity of the light on a specific wavelength? Or is it something else?

Just need to know what the "x" and "y" variables (so to speak) represent.. i've seen diagrams on which there was some text but it was more like the formula not something general like "intensity", which is all i need.
Yes, typically it would be frequency (or equivalently, wavelength) on the X axis and intensity/amplitude/brightness on the Y axis.