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pmedic42777
2007-Jul-22, 06:15 AM
First of high I'm kind of new to astronomy, and new to this site, (as a member).
Any way my question.
I have been help categorize galaxies, for galaxy zoo. I have a lot of questions, and as of yet no answers.
1. What are the differences between elliptical, and spiral galaxies, other then anatomical diffidences?
2. I am seeing a wide varieties of colors, but the green galaxies seem to be rare well like 1 in 100 seem to be green, what makes them green.
3. Do spiral galaxies evolve in to elliptical galaxies?

Thank you. Chuck

Tinaa
2007-Jul-22, 06:24 AM
Welcome pmedic42777Q! Our Q&A section is frequented by very knowledgeable people willing and happy to help answer your questions.

Ken G
2007-Jul-22, 01:50 PM
1. What are the differences between elliptical, and spiral galaxies, other then anatomical diffidences?The amount of angular momentum in the stars. All stars orbit around in a galaxy, but the angular momentum of the galaxy measures their tendency to all be going around the same way in the same plane. Stars in elliptical galaxies don't do that so ellipticals don't have much angular momentum. Stars in spirals usually do, so spirals have a lot of angular momentum. Angular momentum is worth tracking because it can be hard to change its value over time.


2. I am seeing a wide varieties of colors, but the green galaxies seem to be rare well like 1 in 100 seem to be green, what makes them green.The surface temperature of stars control their color, so the color of a galaxy is determined by the average color of the stars. Some colors are more likely than others when dealing with stars. Old stars tend to be reddish, bright stars tend to be blue-white. So if new stars are forming, you will see those bright blue-white ones more than anything, and if no new stars are forming you'll see those old red ones, but it's not so easy to get green.


3. Do spiral galaxies evolve in to elliptical galaxies?
It used to be thought that galaxy type evolved, but now it's generally thought that this is more a measure of the process of initial formation, and that the galaxy type doesn't change unless there is a collision of galaxies. Such "collisions" will cause the type to look "irregular", and after that some evolution may occur. There are also subtypes within spirals and ellipticals, and changes can occur there as the star-forming properties age. So this is actually kind of a tough question, but basically-- ellipticals and spirals are born that way based on the amount of orbital angular momentum in the gas that forms the stars.

Gillianren
2007-Jul-23, 04:40 PM
Welcome to the board! I can't help with astronomy questions--just not my field--but "some" has an "e" at the end, and you only get one exclamation point.

Also, on a more serious note, it helps when posting questions to put more pertinent information in the thread title, such as a short version of your question. It draws more helpful answers, the kind I cannot myself provide.

pmedic42777
2007-Jul-23, 06:04 PM
Thank you, everyone. for your help. I an very excited about helping in this way. But I aslo like to understand the science behind what I am doing, instead of blindly pushing buttons. So thank you all

ngc3314
2007-Jul-23, 07:08 PM
For a little more background, here (http://www.astr.ua.edu/goodies/data_resources/galaxies.text) is some introductory material on galaxies and their structures.

To my mind and eye, there should be practically no (low-redshift) galaxies that look green (any more than there are green stars), except for some with very strong gaseous emission in their spectra. However, automated color balancing won't always be consistent, so some of these will look greenish anyway.

Much more detail on galaxy classification may be found here (http://www.astr.ua.edu/keel/galaxies/classify.html). Come to think of it, that's so much that the GalaxyZoo people might think of it as leading the witness...