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Galaxies.

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Arcane
437100.  Sun Nov 09, 2008 5:55 am Reply with quote

Galaxies, also called nebula.

Galaxy comes from the Greek root word "Galaxias", which means "milky", or "kyklos galaktikos", meaning "milky circle".

Galaxies are categorized by their apparent shape:

Elliptical - ellipse shaped.
Spiral - disc shaped with curving arms.
Peculiar - unusually shaped.
Starburst - where two galaxies meet.
Irregular - lacking in a coherent structure.

Galaxies are sized from Dwarf (which may have 10 million stars) through to Giants (which may have up to a trillion stars). They contain multiple star systems, start clusters and interstellar clouds.

There may be more than 100 billion galaxies in the observable universe.

The mass of a galaxy may be 90% dark matter.

Recent research states that scientists may be coming close to solving the riddle of what dark matter is. Dark matter article


The word galaxy was first used in the English Language in a poem by Chaucer.

Here are some fantastic pictures taken by the Hubble Telescope of galaxies.

Wow.

A site with links to all sorts of excellent articles and pictures about galaxies:

http://www.space.com/galaxy/

source: Wiki article "Galaxy".

 
Davini994
437130.  Sun Nov 09, 2008 7:12 am Reply with quote

Hoag's Object:



The stars round the ring are bright and blue, the nucleus is older and yellow. The diameter of the disk is slightly larger than the milky way.

Which is interesting because we haven't really got a barneys how it formed, although we've worked up to some confident sounding waffle about a small galaxy travelling through a larger one.

Quite pretty too, no?

 
Davini994
437137.  Sun Nov 09, 2008 7:22 am Reply with quote

Reddygirl wrote:
The mass of a galaxy may be 90% dark matter.

This figure is far too high by the majority of scientists today. It's only put that high by those whose funding depends on it, and amateur amazed articles in papers and the like. IMO.

About 30% is more realistic I'd say.

Edit for typo.


Last edited by Davini994 on Sun Nov 09, 2008 11:24 am; edited 1 time in total

 
Rudolph Hucker
437195.  Sun Nov 09, 2008 9:37 am Reply with quote

I tend to agree with Davini994;

If Dark Matter were to exceed that sort of percentage, the nature of the observed Galaxies would change to such an extent that they would have to be re-classified as plain chocolate.

 
Arcane
437436.  Sun Nov 09, 2008 5:12 pm Reply with quote

In several articles I've read, 90% was the most common figure quoted.

Do you have any articles that quote the "more realistic" figures you speak of?

 
mckeonj
437457.  Sun Nov 09, 2008 5:27 pm Reply with quote

If 100 angels danced on the head of a pin, what percentage would fall off by the end of the measure?

 
Posital
437463.  Sun Nov 09, 2008 5:37 pm Reply with quote

mckeonj wrote:
If 100 angels danced on the head of a pin, what percentage would fall off by the end of the measure?


None - everyone know's there's space for at least half a million angels without any significant elbowing during the dance.

PS: 90% of all dark matter will be proved to be constituted by dancing angels and seraphim.

 
bobwilson
437465.  Sun Nov 09, 2008 5:39 pm Reply with quote

Quote:
PS: 90% of all dark matter will be proved to be constituted by dancing angels and seraphim.


But surely angels aren't dark?

 
Sheriff Fatman
437478.  Sun Nov 09, 2008 5:59 pm Reply with quote

bobwilson wrote:
Quote:
PS: 90% of all dark matter will be proved to be constituted by dancing angels and seraphim.


But surely angels aren't dark?


http://en.wikipedia.org/wiki/Dark_Angel_(TV_series)

 
Posital
437484.  Sun Nov 09, 2008 6:04 pm Reply with quote

bobwilson wrote:
But surely angels aren't dark?


Obama made it possible.

 
dr.bob
437788.  Mon Nov 10, 2008 10:59 am Reply with quote

reddygirl wrote:
Galaxies, also called nebula.


Or not.

Nebulae are rather different things to galaxies. They're an awful lot smaller for one thing.

One class of galaxy you forgot to mention is barred spirals. They're just like spiral galaxies, but have a central bar, like this:

 
Davini994
437882.  Mon Nov 10, 2008 1:34 pm Reply with quote

Ooh, hypnotic.

 
mckeonj
437949.  Mon Nov 10, 2008 4:18 pm Reply with quote

Nebula M38 (Hubble telescope)

Starry Night (Vincent van Gogh)

Whirlpool Galaxy M51 sketched by the Earl of Rosse

There is an intriguing similarity between van Gogh's "mad spirals" and the spiral galaxies sketched by William Parsons, the Earl of Rosse. van Gogh was in the habit of transferring photographs and drawings to canvas, even copying his own work.
He was working in London at the time that the Rosse drawings were published in the London newspapers, and presumably copied the spirals into his work. Another of his paintings, of the empty chair, is a dead ringer for an illustration in one of Charles Dickens novels.

 
Arcane
437957.  Mon Nov 10, 2008 4:30 pm Reply with quote

The barrel shaped galaxy you pictured dr.bob is quite lovely!

Although, would it be considered a spiral galaxy because of it's overall shape, even though it has a differing structure in the middle?

 
dr.bob
438163.  Tue Nov 11, 2008 6:11 am Reply with quote

Yeah, that's a fair point. It is mostly spiral, after all. However it seems to be common among astronomers to count spirals and barred spirals as two different classes of galaxy. I'm not entirely sure why.

 

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