Galaxies and the Milky Way — Astronomy, 11–13 years
Stars are gathered into enormous systems called galaxies. Our Sun belongs to the Milky Way, one spiral galaxy among billions.
A galaxy is a star city
A galaxy is a huge collection of stars, gas, dust and dark matter held together by gravity. Some galaxies are spiral-shaped, some are oval, and some have less regular shapes. The Milky Way is a spiral galaxy, and the Solar System sits in one of its quieter outer regions.
Why look beyond our stars?
For a long time, a cloudy band across the night sky looked like a single glowing path. Careful observations showed that it contains countless distant stars, and that other fuzzy patches are separate galaxies. Thinking in galaxies solved the problem of understanding the true scale of the universe.
Finding our address
Start with Earth. Earth orbits the Sun, so our first address is the Solar System. The Sun and its neighbours lie in the Milky Way, so add that galaxy. The Milky Way belongs to a small gathering called the Local Group. Our full address is Earth, Solar System, Milky Way, Local Group, universe.
The Milky Way is not the whole universe
It is easy to call the pale band in the sky “the universe”, because it stretches so far and contains more stars than we can count. It is actually the view from inside our own galaxy. Other galaxies exist far beyond it, even though most are too faint to see without a telescope.
Maps of the largest neighbourhood
Astronomers classify galaxies by their shapes and measure how they move and cluster. These maps reveal where matter is concentrated and help test ideas about how the universe changes. When you see a galaxy image, you are seeing its ancient light, because that light travelled for millions or billions of years.
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