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 Asteroid Hunt project to learn more.) If an asteroid moves slowly, it shows up as a blue dot next to a yellow dot. Fast-moving asteroids show up as a red, green and blue dot. Very fast asteroids 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 “object type” is listed as star.
Galaxies form in clusters of dozens or hundreds. The SDSS has seen many clusters, including the one 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!
Sometimes, when the SDSS telescope looks at a very bright object, the object’s light is reflected inside the telescope. These reflections can cause “ghosts.”
Ghosts are bands of light. They are usually a single color; either red, green or blue, depending on which filter the camera was looking through. A typical ghost is shown at the right.
Now you’re ready for the scavenger hunt! Click Next to get started.