Stardial Assignment
logonvy.gif - 4742 Bytes     Assignment: Track a Bright Asteroid

  The purpose of this Stardial exercise is to become acquainted with the Stardial image archive and to see changes in the night sky from one night to the next. You will see obvious changes, such as cloudy or clear nights, and you will see some subtle changes, such as an asteroid drifting across the field of view. You will plot the location of the asteroid and determine its rate and direction of its motion on the sky. There's a surprise for the alert observers...see the last question.

You will see how asteroids appear to move on the sky by observing one of the largest asteroids in the main asteroid belt. Asteroids are also called minor planets, and the main asteroid belt is located between Mars and Jupiter. See your textbook and notes for definitions of any unfamiliar words.


  1. Stardial is accessible from the class' homepage. Read about Stardial by clicking on What is Stardial? and then How does Stardial work?.
  2. You will study images from 1997 of the Stardial field, RA=0145. That stands for Right Ascension (RA) = 01 hour 45 minutes.
  3. The asteroid is at the far right hand side of this image (click here)
  4. To get the images of interest, follow these directions for accessing Stardial images.

    1. From Stardial homepage, click on Data.
    2. Read about the description of the data archive by clicking on location on the sky.
    3. Return to Data by hitting the Back key on the browser.
    4. To access the data, click on Archive via the Web. (shortcut = "Web" from the homepage)
    5. Then click on jpg (for jpeg data format).
    6. Then click on RA (for right ascension cataloging).
    7. Then click on 0145 (for the RA=0145 field).
    8. Then click on 1997 (for data in the year 1997).
    9. You should now be on the page which lists all the images by date in that year. For example, if you click on 1004.jpg you will be viewing the image of the star field RA=0145 on the date 10/04/1997. Note that often the whole stardial image does not appear all at once on the may need to click on the bottom scroll-bar to view the right portion of the image. If possible, enlarge your browser window to fill the entire TV monitor. If you do that, you may not have to use the scroll-bar at the bottom of the screen at all.
    10. Note that if the screen comes up completely white, then you have selected a completely cloudy image. Tip on avoiding cloudy images: If you look in the third column under size, you will notice numbers like 10K, 26 K, etc. These are the size of the image file in kilobytes. Completely cloudy nights have sizes of around 10 K or less; so pick another image.
  5. You are to search the archive for RA=0145 on all clear or partially clear nights from 10/03/1997 to 10/21/1997. Follow steps 1-10 above and answer these questions.

  1. Which nights were clear? Which were partly cloudy? Which were totally obliterated (so Stardial's image is all white)?
  2. For each night that was clear enough to see the asteroid, mark an X at the location of the asteroid on this image (click here). (It's printed as a negative to make your marking's more legible.) Label each X that you plotted on your image with the date that corresponds to the X.

  3. Judging from your images, what direction does the asteroid appear to be moving on the sky?
  4. Note that RA increases in the eastern direction, while declination (DEC) increases in the northern direction. Is the RA of the asteroid increasing or decreasing with time? What about its DEC?
  5. The Stardial image is 8° by 5°. Using a ruler, estimate the rate of the asteroid's apparent motion. Express your answer both in ° /day (degrees per day) and in "/min (arcseconds per minute). Astronomers call the apparent motion on the sky "proper motion."
  6. Was the asteroid in prograde or retrograde motion?
  7. Based upon the previous question, was the asteroid closest to A) opposition, B) conjunction, or C) 90 degrees away from the Sun as seen from Earth?
  8. Based upon the previous two questions, draw an approximately-to-scale heliocentric diagram as seen from far above the ecliptic plane showing the positions of the Sun, the Earth and the asteroid in relation to each other. Draw the asteroid and the Earth twice, once for the first day and once for the last day of your observations; label the Earth and the asteroid and indicate which one is on the first day and which is on the last day. Your textbook has similar diagrams illustrating the concepts of prograde and retrograde orbits.
  9. The asteroid in this lab is one of the brightest in the solar system. In principle, it could have been discovered before the invention of the telescope, but it wasn't. It was approximately 6th magnitude when those Stardial images were taken. The unaided human eye can see 6th magnitude objects, but not fainter ones. Approximately how many stars in the 8° by 5° image are brighter than the 6th magnitude asteroid? Count them. (The brighter stars appear larger on the image than do fainter stars.) There are approximately 41,253 square degrees on the entire celestial sphere, so based upon your count of stars in this image, estimate the number of stars on the entire celestial sphere that are visible to the unaided eye.
  10. Finally, there were some other objects besides stars and clouds visible on these images. Did you notice any? Describe what you saw phenomenologically, and then interpret your observations, i.e. take a guess as to what you think caused the phenomenon that you noted. Hint: some of them are described elsewhere in the Stardial Website.