Homework: measuring the parallax shift of 1998WT

2:35 PM Wednesday, March 16: fixed a typo in item 2 of the list at end. The year should be 2005, not 2004. MWR

On UT March 4, 2005, astronomers at Yerkes Observatory (near Williams Bay, Wisconsin) and at Gettysburg College (in Gettysburg, Pennsylvania), observed the asteroid 1998WT simultaneously. Because they were looking from different locations on Earth, they saw the asteroid appear at slightly different places in the sky. If one can measure the difference in the asteroid's position, one can estimate the distance to the asteroid.

Your job today is to measure the (RA, Dec) position of the asteroid as seen from the two observatories. Below are closeups of the images obtained by each observatory at 02:45 UT March 4, 2005.

First, from Yerkes. It's easy to identify the asteroid in this picture, as it was moving so fast that it left a short streak.

Now, from Gettysburg (this is just a portion of the entire image, focusing on the asteroid). Because this image had a shorter exposure time, and because it has a slightly blurrier PSF, it isn't as easy to pick out the asteroid. Compare it to the image above, though, and you should find it.

You might want to print out copies of these images for reference ...

Now, to measure the position of the asteroid, I suggest that you use the Aladin tool.

Start up Aladin in a browser
Choose the Load item, and provide the coordinates of the asteroid at UT 2005 March 4, 02:45:00. Don't know the coordinates? Look them up on the JPL Horizons ephemeris generator If you can't figure out the asteroid's coordinates, ask me.
Aladin should give you a list of possible images to examine. Choose the POSS I E(optical R) 13.9'x13.9' image, and click on Select. After a brief delay, Aladin's image window should bring up a picture of the sky which matches the images above, though it will be a bit larger.
Zoom the Aladin image to the "2x" level. That should make a better match to the observed images.
If you wish, right-click on the Aladin picture and choose "Reticle off" (to turn off the purple crosshair), and/or "Grid on" (to overlay a coordinate grid).
Now, move your cursor to the position of the asteroid in the Yerkes image. The coordinate display near the top of the Aladin window should follow your cursor's motion. Write down the (RA, Dec) coordinates of the asteroid in the Yerkes image.
Repeat to estimate the (RA, Dec) position of the asteroid in the Gettysburg image.
Make a table showing the position of the asteroid in the two images. Provide (RA, Dec) for each image in two formats:
1. "Babylonian": HH:MM:SS.ss and +DD:MM:SS.s (for example, 01:23:45.56 +07:33:34.3)
2. "decimal degrees": DDD.dddd and +DD.dddd (for example, 20.93983 +07.55953)

For more information

More information about asteroid 1998WT and these simultaneous images.