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Slide Notes

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Published on Jan 01, 2021

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By Gloria M.

What Are Galaxies?

Galaxies are what make up the cosmos, with as many as 170 billion in our observable universe. That basically means anything that we can see through telescopes, the naked eye, etc. Yet there is still a future visibility limit, things we can't see. Galaxies also compose of gas, dust and billions of stars.

Photo by Mason Field

Stars, Planets, Solar Systems

On a clear night sky, what do you see? Can you see stars? If you look close enough, Venus? Our galaxy contains all these marvellous parts! With stars being one of the main parts of galaxies, you can expect to see them on a cloudless evening. From what we know, most stars in our galaxy have planets orbiting around them. That means there must be more than millions. There are countless possibilities!

Photo by nist6ss

Black Holes

Believe it or not, galaxies are not just about stars. Scientists believe that there are supermassive black holes at the centre of nearly every galaxy – including our own. The gravitational pull of black holes anchor galaxies together in space. There appears to be a massive black hole at the heart of the Milky Way called Sagittarius A. Since black holes don't suck, this is possible.

Photo by jurvetson

Intergalactic space

In the same way the length between stars is known as interstellar space, intergalactic space is the distance between galaxies. They are the vast voids that sit between galaxies. For instance, if you were to travel from the Milky Way to the Andromeda galaxy, you would need to cross 2.5 million light-years of intergalactic space.

Photo by Jeremy Thomas


  • Spiral Galaxies
  • Elliptical Galaxies
  • Irregular Galaxies
  • Lenticular Galaxies
Photo by duncan

Spiral Galaxies

A spiral galaxy is a mix of stars and gas that is often beautiful and contains young, hot stars. The Milky Way, in fact, is a spiral galaxy! They usually contain supermassive black holes in their center.

Elliptical Galaxies

Elliptical galaxies display a smooth, almost featureless brightness profile. The shapes of elliptical galaxies vary from nearly spherical to nearly flat.

Irregular Galaxies

An irregular galaxy has no distinct form, like a spiral or elliptical galaxy. About a quarter of all galaxies are irregular. There are three kinds of irregular galaxies: Irr-I galaxies, Irr-II galaxies, and dwarf irregulars.

Photo by sjrankin

Lenticular Galaxies

Lenticular galaxies are one type of irregular galaxy. They have an elliptical shape and their structure resembles that of a disc. These galaxies are a mixture of spiral and elliptical galaxies.

Photo by Arnaud Mariat

Here is a list of known galaxies:

  • Andromeda Galaxy
  • Canis Major Dwarf Galaxy
  • Cygnus A Galaxy
  • Maffei I and II Galaxy
  • Magellanic Clouds Galaxy
  • Virgo A Galaxy
  • Milky Way Galaxy