I’m tempted to say that galaxies began a long long time ago somewhere far far away, that would be true but it wouldn’t help much. A galaxy is the name we give to any very large collection of stars that are held together by gravity. How many stars? Well, that can vary a lot, we’re not even sure how many stars make up our home Milky Way galaxy because it’s so difficult to count them but there’s probably around the 200 to 300 billion of them.
It’s very difficult to visualise just what those numbers mean, for most of us numbers like these are just too big. To help you visualise this, imagine stacking up a million pennies they would reach up over 1.5 kilometres. Do the same thing with a billion pennies, and they would be heading towards hundred kilometres, so 300 billion is a truly vast number of stars.
What shape is a galaxy?
Most galaxies including our own are shaped like spirals with a central blob and some arms spiralling out. If you’ve ever looked at the sky on a truly clear dark night, you’ll have noticed a smear of light arching across the sky, what is usually called the milky way. This is one of the spiral arms of our galaxy, look at it through a telescope and you’ll see that the smear of light is made up of a vast number of stars a very long way away. Not all galaxies are spiral shaped, there are lenticular galaxies, lens shaped, irregular ones that have no particular shape, elliptical and rarely there are ring galaxies. How they all got into the shapes that we see them is a huge and sometimes debated subject, but generally a spiral galaxy gets that way through something called conservation of momentum which is a subject I’ll save for another time. Suffice to say it’s a bit like a spinning ice skater going faster as they bring their outstretched arms inwards.
Do galaxies collide?
Yes they do, in a few billions of years we will collide with our nearest neighbour the Andromeda galaxy. It’s no big deal though, mostly they just pass through each other, but gravity will scatter the stars all over the place.
I just said that the Andromeda galaxy is our nearest neighbour, but that’s not strictly true, in the southern hemisphere you can see two irregularly shaped dwarf galaxies, the large and small Magellanic clouds. These are interesting places to an astronomer, they seem to have a lot of stuff in them that has yet to come together to form in to stars, and probably a lot of dark matter too, which is something else we really don’t understand.
The evolution of galaxies since the big bang is a subject that is only partly understood, observations made by the James Webb telescope out in space have upset the apple-cart of knowledge, but I reckon that’s a good thing. It’s good the be reminded about how little we know and how much more there is yet to discover.
This month’s picture of the whirlpool galaxy is by Ron Giddy, a fellow amateur in our group.
Charles Oates, Vega Baja Astronomy Group.
● To find out more about observing and astronomy why not join our group, email us at vegabaja.astronomygroup@gmail.com to find out more.
