Groups of Stars

In our Milky Way Galaxy stars can arrange themselves in: Globular clusters A collection of hundreds of thousands of stars in a small area These tend to orbit around the centers of galaxies Believed to be very old stars Our Milky Way Galaxy has at least 150 globular clusters

In our Milky Way Galaxy stars can arrange themselves in: Open clusters A close arrangement of a small number of stars Thought to be created at the same time from the same nebula Eventually they move away from each other

Pleadies Star Cluster (also known as the ‘seven sisters’)

In our Milky Way Galaxy stars can arrange themselves in: Constellations An arrangement of stars that form a recognizable pattern in the sky Very useful to find other celestial objects such as planets, nebula, other galaxies, etc.

The Big Dipper Also known as Ursa Major – great bear

Casseopeia

Cygnus – the northern cross

Orion – the hunter

Canis Major – greater dog

Winter Triangle The three stars of the winter triangle Procyon Sirius (canus major) Betelgeuse (orion)

Pointer Stars

Pointer Stars from the Big Dipper

Galaxies Galaxies are huge formations of millions of stars and clouds of dust (nebula) They come in many different shapes and sizes

Spiral Galaxies These galaxies have very distinct shapes with spiral arms radiating from their centers. Our own Milky Way Galaxy is a spiral galaxy.

Barred spiral galaxy Similar to a spiral galaxy, but with only two distinct arms and an elongated or ‘barred’ central core of stars.

Elliptical Galaxies Elliptical galaxies have an ovoid shape and consist mainly of very old stars with no new star formation processes.

Irregular Galaxies Large Magellanic Cloud Small Magellanic Cloud Both of these irregular galaxies are small satellite galaxies of the Milky Way.

Location of the Andromeda Galaxy

A supermassive black hole at the center of a galaxy.

Groups of Galaxies Galaxies tend to form in groups. Our Milky Way galaxy is part of the Local Group of galaxies that includes the Andromeda Galaxy and the Large and Small Magellanic Clouds. There are 30 known galaxies in our group of galaxies. Some galaxy clusters contain hundreds or even thousands of galaxies.

Galaxy Collisions There is lots of evidence that Galaxies have ‘collided’ with each other or are on a collision path with each other. The collisions can change the shape of the galaxies and can also result in the exchange of materials between the two galaxies.

Hubble Deep Field View Looking at a piece of the sky no wider than the width of a dime at 75 feet away Hubble found about 1500 galaxies which takes the estimated number of galaxies in the universe into the billions!!