Bringing order to the zoo of galaxies

Before we start doing any calculations, it might be a good idea to look around us and make an inventory of what types of galaxies are out there. There are many good web pages to start, for example I like http://www.taas.org/gnto/astropic.html, because it shows pictures made with a small telescope - so those are galaxies as you might have seen them yourself, if you are an amateur astronomer. http://www.aao.gov.au/images.html/ shows professional images. Such professional pages (for example the Hubble Space Telescope (HST) archive) tend to contain a large fraction of unusual galaxies - simply because those are the ones that astronomers tend to study.