Astronomy 150 | Spring 2012

Computer Lab 1: Astrometry of Asteroids

Purpose: To introduce students to the techniques that astronomers use to discover asteroids and to measure their coordinates in the sky.

Goals:

• You should be able to understand how moving objects can be discovered on images of the sky.
• You should understand the fundamentals of using the equatorial coordinate system of right ascension and declination to locate objects on the sky.
• You should understand how reference stars of known coordinates can be used to interpolate the coordinates of unknown objects.
• You should appreciate the way in which astronomers measure parallax and use it to determine the distance to objects in the solar system and beyond the solar system.

Lab Description: This exercise incorporates software designed to find asteroids using digital images of the sky taken at different times, along with software designed to measure the precise positions of stars on images. It also includes several digital images of asteroids taken at research observatories and documentation for both the students and the instructor.

In the first part of the exercise, students view pairs of images of the sky, align them so the stars overlap, and "blink" them to highlight moving objects...asteroids. Once an asteroid is identified, the software can display a chart of the star field around the asteroid by calling up positions of stars from a reference catalog (a selection of the Hubble Guide Star Catalog included with the software). By identifying at least three reference stars from the catalog with stars on the digital images, the software can then proceed to determine the astronomical coordinates of the asteroid (right ascension and declination) to a precision of about 0.1 seconds of arc. Measurements of the asteroid coordinates on several images taken at different time yields the angular speed of the asteroid.

In the second part of the exercise, students analyze two images of an the same asteroid taken at the same time from sites several thousand kilometers apart (Flagstaff, Arizona and Hamilton, New York). Because of parallax, the asteroid appears at different positions on the two images. Measuring the asteroid's coordinates on both images, and knowing the baseline separating the two sites, yields the distance to the asteroid. Combining this result with the angular speed of the asteroid from part one yields the tangential velocity of the asteroid.

Lab Software: The program we will use (ASTROMETRY OF ASTEROIDS) can be downloaded to your computer, or you can go to any of the ICS computer labs (running Windows). The software is available under "Class Software | ASTR150" on the "Win_Apps" menu.

If you want to install on your own machine,there is a link below to download the program (be sure to do a "complete" installation, or the software will not install the images for the extra credit section of the lab). To access the program from an ICS lab, look under ASTRO 150 in the Class Software section of the Start menu.

Lab Groups: You may work on this lab in groups of up to 3 people. A single lab report can be turned in for the group (with all group member names and NetIDs, of course).

Due Date: The completed Lab Worksheet below is due in class Friday, March 2.

Help Sessions: Help sessions will be conducted on March 1 from 5-7pm in the Oregon ICS Lab.

Downloads:

• AsteroidLabManual.pdf - Instructions for using the software and completing the lab exercise.
• AsteroidLabWorksheet.pdf - This is what you will print out, complete, and turn in.
• Astrometry of Asteroids software package: AstrmLab.EXE (Windows only)- Download and run this file only if you wish to install the lab software on your own PC.