The Universe & Galaxies Key Point (Std 8-4.9): Recall the Sun’s position in the universe, the shapes and composition of galaxies, and the distance measurement unit (light year) needed to identify star and galaxy locations.

Universe All of the matter (and anti- matter) which exists. Made up of galaxies which contain solar systems which contain stars, planets, asteroids, comets, meteoroids and ‘dark matter’.

Star, planets, moons, asteroids, comets, meteoroids Solar System Galaxy Universe

Galaxies made up of gas, dust, and billions of stars Gravity keeps it together and can also tear it apart Have different shapes: 1) elliptical spherical or flattened disks 3) irregular a nucleus of bright stars and two or more arms (barred or pinwheel) 2) spiral no definite shape

Milky Way Galaxy We live here. It is a large, barred spiral galaxy containing possibly 400 billion stars plus dark matter Second largest member of the “Local Group” (Andromeda is biggest)

Our Sun a main sequence star halfway through its life- cycle located on a spiral arm about 2/3 of the way from the center of the Milky Way galaxy

Light year Because distances in space are so great that conventional numbers are too large to work with, astronomers use this unit of measurement to measure the distance to stars and galaxies in space. 1 light year = the distance light travelled in one of our years It is just under 10 trillion km or 6 trillion miles.

Some cool light year facts The most distant space probe, Voyager 1, is travelling 38,000 mph and will take 17,500 years to reach one light year. The nearest known star, Proxima Centauri, is about 4.22 light years away. The center of the Milky Way is about 26,000 light years away! The Andromeda Galaxy is approximately 2.5 million light years away!