Question: How are galaxies, clusters, and nebulas different?

Freya Addison answered on 22 Nov 2019:

Joanna and Heidi will probably be able to answer this better.
However usually a galaxy has a supermassive black hole in the centre which through gravity bounds stars, dust and systems around it. You get different types of galaxies: Spiral (like the milky way). Elliptical (typically old). Irregular (weird shapes). Merging (multiple galaxies colliding). Galaxies are really big and contain nebulas and clusters. (The zooniverse project is a really cool citizen science website where you can help classify galaxies: http://zoo1.galaxyzoo.org/)
A nebula is a cloud of gas and dust. Stars are born from dense nebula in stellar nurseries such as the “Mystic Mountain” in the Carina Nebula. However nebulas such as the “Cats Eye” Nebula, is a planetary nebula, so when a low mass star dies and strips off its outer layers (not quite a supernova which is from a high mass star) leaving layers of cloud and dust.
Clusters you have two types. Globular clusters which is a very dense region of stars and is very spherical. Open clusters only have a few thousand stars and although bound by gravity aren’t quite as tight.