Observing Project 9A Tracking Asteroids

With a little bit of effort, you can learn the location of just about any asteroid in the sky for the purposes of planning an observing session. Popular astronomy magazines will publish articles containing finder charts when asteroids of note are favorably placed for viewing. You can also find the location of most asteroids using just about any planetarium program. After that finding your target is up to you.

The problem with locating an asteroid as opposed to some other faint object like Uranus or Neptune is that they look like any other star. Uranus or Neptune clearly do not look like stars in a telescope. Picking an asteroid out of the background requires that you know what point of light in the picture is the one that does not

28 This shower is named for the now defunct constellation Quadrans, which is now in the northeastern area of Bootes.

belong there. Imaging the area where you believe the asteroid is located with your telescope will show clearly that one of the points of light in the field will move over the course of a few days. If you do not have a camera, then make drawings of the area over the course of a few days. Use low to moderate power in your telescope and chart the motion of your asteroid in a field of view that is about one to one and a half degrees wide.

It is also interesting to note the wide variety of patterns that an asteroid makes as it nears and passes opposition. Because the planets all orbit in close to the same plane as Earth, the retrograde patterns that they make can be very subtle. The planets tend to make narrow loops or "Z" shapes that have very narrow declination spreads. Some asteroids have orbital inclinations that are well offset from that of Earth. Of the Big Four, Ceres and Vesta orbit close to the plane of the ecliptic while Juno and Pallas have orbits that are more highly inclined. Pallas in particular because it is in an orbit inclined 34 degrees to the ecliptic can make patterns in the sky that are much more exaggerated than Ceres might make. You can plot the motions of both asteroids against the sky over several months around the time of opposition and see the difference for yourself.

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