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[Chicago Astronomer - Astro Joe]

Andromeda is Three Times Larger Than Previously Believed

(May 30, 2005) Astronomers from the US and France have mapped out the motion of a stars in the outskirts of the Andromeda galaxy (M31), and found that they're actually part of the galaxy's main disk. This means that this spiral galaxy is actually three times larger - 220,000 light years across - than astronomers had previously estimated.

It was previously believed that these stars were part of a halo that surrounded Andromeda, but weren't actually part of its disk. This discovery hadn't been made until now because detecting the motion of these stars requires very precise observations.

More here from Universe Today: www.universetoday.com/am/publish/andromeda_3_times_larger.html?3052005

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I enjoy observing this object in my scope, although like a dim cotton ball, I'm actually looking at an entire galaxy! And now...it's bigger than ever!...too cool...

[Maddad]

Althought the Universe Today article is dated yesterday, I read another article like it a month or so ago talking about this. It has implications for the sizes of all galaxies, not just Andromeda. They all might be larger than we previously thought.

On another forum they were suggesting that because of the way we estimate the mass and its distribution in a galaxy, we may need less dark matter to explain rotation speeds than we did before. This in turn means that the universe would be composed a greater percentage of visible matter.

That the galaxy is larger does not necessarily mean though that it is more massive than we previously believed. It just means that we re-lable previously known mass as properly belonging to Andromeda instead of just being near it.

[Chicago Astronomer - Astro Joe]

I'm in agreement.

The neighborhood surrounding galaxies and other bodies will grow with better intrumentation and time to calculate.

I'm still impressed with the news of the Ursa Major being a very open star cluster and travelling together.