A quick side note here to explain a light year. Light is the fastest thing in the Universe and travels at 300,000km per second. At that speed, light can travel 9.5 million million km in one year. We use this distance as in scale in astronomy so 1 light year equates to 9.5 million million km. The nearest galaxy to our own, the Andromeda galaxy is just over 2.3 million light years away. That’s a whole lot easier to say, and deal with, than 21.8 million million million km! And that’s the nearest! A the time of writing, the most distant object discovered is a galaxy about 13.4 billion light years away! Needless to say, galaxies are a long way away!
Our own galaxy, the Milky Way gives some idea of the scale of galaxies, measuring about 100,000 light years across and our own Solar System is about 2/3 of the way out from the centre. For many years, it was thought that the Milky Way belongs to a class of galaxy called a spiral galaxy but recent studies suggest this may not be the case. You can imagine its rough shape though by visualising two fried eggs stuck back to back, the yoke representing the bulge of the nucleus and the white representing the disk of the spiral arms. Galaxies come in a number of different shapes, from the spiral galaxies similar to the Milky Way and Andromeda Galaxy, to barred spirals, vast elliptical galaxies and irregular galaxies.
Like all things, gravity plays a big part in the lives of a galaxy. Its the thing that holds it together but is also the force that binds galaxies together into gigantic galactic clusters. Our own Milky Way galaxy is a member of what we call the Local Group which has about 33 members. Two of those members are our satellite galaxies, the Large and Small Megallanic Clouds which are visible from southern latitudes.
Some of the most distant objects visible are super bright galaxies and many of them were formed when the Universe was just a fraction of its current age. Its thought the powerhouse at the centre of these young galaxies is a supermassive black hole, swallowing up matter at a colossal rate. Just before the matter falls into the black hole it will have been accelerated to incredible speeds, spinning round so fast and is imparted with incredible amounts of energy that it gives off a phenomenal amount of light which we can detect. Its actually thought that all galaxies, our own included, have black holes at their core
Mark’s Observing Tip
For observing galaxies, bigger really is better. Galaxies are typically quite faint in the sky so the bigger your telescope, the brighter the image you will see and the more detail you will enjoy.