Types of Objects

Stars

The SDSS observes lots of stars. Stars are giant balls of gas that release energy by burning hydrogen at their cores. When they run out of hydrogen, they can release energy by burning other elements. Eventually, their fuel supply runs out and they die.

Star Clusters

A star cluster Click on the image for a larger view

Stars frequently are found in very densely packed clusters of hundreds of stars. There are many types of clusters. A typical star cluster seen by the SDSS is shown at the right.

Galaxies

Galaxies are huge collections of stars. Our galaxy, The Milky Way, may contain up to a trillion stars - no one is exactly sure how many. Other galaxies can be even larger, while some "dwarf" galaxies are much smaller.

Galaxies come in different shapes. The three types of galaxies are spiral, elliptical, and irregular. Spiral galaxies are "face-on" when you see the spiral shape and "edge-on" when you see them from the side. Examples of each type are shown below.

An elliptical galaxy	A face-on spiral galaxy	An edge-on spiral galaxy with a visible dust lane	An irregular galaxy

Sometimes galaxies pass close to each other. When they do, their gravity can cause them to interact with each other. The galaxies can bend each other, making them look like the pair shown below.

A pair of interacting galaxies

Asteroids

Asteroids are small pieces of rock that orbit the Sun, mostly between Mars and Jupiter. Asteroids move quickly across the sky, so they can be seen in SDSS images (see the Asteroids project to learn more). If an asteroid moves slowly, it will show up in images as a blue dot next to a yellow dot. Fast moving asteroids show up as a red, green and blue dot in succession. Very fast moving asteroids may appear as a single colored streak. Examples of each type are shown below. Asteroids that appear as blue-yellow dots trick the computer program that classifies objects, so their types are listed as stars.

A slow-moving asteroid	A slightly faster asteroid in front of a galaxy	A very fast-moving asteroid

Galaxy Clusters

A galaxy cluster Click on the image for a larger view

Galaxies form in clusters of dozens or hundreds. The SDSS has seen many clusters, including the cluster Abell 0957 shown at the right. Galaxy clusters can be so far away that individual galaxies almost look like stars!

When you see a cluster in the Navigation tool, click on one of the objects to see the object type. You might be surprised to find what you thought was a star cluster is actually a galaxy cluster!

"Ghosts"

A "ghost"

Sometimes, when the SDSS telescope looks at a very bright object, the object's light is reflected inside the telescope. These objects can cause "ghosts". Ghosts are bands of light that appear on the images. They are usually a single color, either red, green or blue, depending on which filter was used when the ghost occurred. A typical ghost is seen at the right.

Now you're ready for the scavenger hunt! Click Next to see what objects you'll be searching for.