In a recent paper, by blah and blah, we have been asked to vote for an official definition of a galaxy. That's easy, I hear you cry: you proceed to draw me an S shaped squiggle on a piece of paper, or even a few fuzzy blobs - not all galaxies are spirals of course.
Or perhaps I underestimate you - maybe you'd answer as I did; that a galaxy is purely a collection of stars, gravitationally bound to eachother. Or perhaps you'd suggest some more complicated; a scientific properti
The thing is - one thing I'm sure we could agree on is the definition; "I know a galaxy when I see one" - or do we..? The reason the paper has been written is specifically for the galaxies we can't easily see, dwarf spheroidals - gravititationally bound star systems, but so faint, and so diffuse, that we barely see them on the sky with our telescopes.
The problem is that there are groups of gravitationally bound stars, called globular clusters
A recent paper has been written, a first of it's kind, called "What is a Galaxy", with the oppportunity for you to cast your vote on the website. They hope, perhaps, to do for galaxies what planet-ists did to Pluto - to make an executive definition of a galaxy, which will separate some galaxy-like objects, from others. In fact, they even give you the opportunity to vote; and if you're interested, I'd certainly recommend you checking this link.
But... do we need to?
A planet is something which can have a definition, and which can be mistaken for another object, but I don't quite see galaxies in this way.
1. What are we trying to rule out? What ISN'T A GALAXY.
Are there any embarassing, galaxy like objects,or debates, in the same vein as Pluto, which need to be put to rest. No.
2. Do we understand enough to be able to define a galaxy? No... we don't reallly know how they are formed.
3. How will science change if we define a galaxy. It won't.
So by all means, vote on the subject; here's the link: but don't expect quite the shift in our spectrum as thought that planetary definition, or our first observations of galaxies brought us. And don't think of this as any more than an academic issue.
