Astronomy 150 | Spring 2012

Computer Lab 2: Solar Rotation

Purpose: To introduce students to the techniques that astronomers use to measure the rotation rate of the sun using images of sunspots. To introduce some of the difficulties of using two-dimensional images to derive three-dimensional properties of celestial objects.

Goals:

• You should be able to state the direction of rotation of the Sun as seen from the earth.
• You should be able to state the rate of rotation of the Sun.
• You should be able to explain how rate of rotation of the Sun can be determined from observations of sunspots.
• You should should be able to describe the appearance of sunspots.
• You should develop an appreciation of the complexities in interpreting two-dimensional photographs of the three-dimensional Sun as observed from the moving earth.
• You should develop an appreciation of the difficulty of turning images into meaningful scientific information.

Lab Description: This exercise enables students to measure the rate of rotation of the sun at various latitudes using an archive of 368 images of the sun obtained over a four month span in 2002 obtained by the Global Oscillation Network Group (GONG) project . Because of the high spatial and temporal resolution of the sample, these are the best images to date from which students can determine the solar rotation rate. Software provided enables student to access the GONG images, display them as still images or animations, measure and record the positions of sunspots, plot its heliocentric coordinates versus time, and thus determine the apparent rotation period of the spot.

Lab Software: The program we will use (THE PERIOD OF ROTATION OF THE SUN) 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 (note - download is quite large ~400 MB, due to the size of the image database).

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, April 20.

Help Sessions: Help sessions will be conducted on April 19 from 5-7pm in the Oregon ICS Lab.

Downloads:

• SolarLabManual.pdf - Instructions for using the software and completing the lab exercise. This includes the lab worksheet and data table templates to turn in.
• The Period of Rotation of the Sun software package (Windows only) - Download and run this file only if you wish to install the lab software on your own PC. Warning - this is a large download, about 400 MB! (If you get a "bandwidth error", its because file downloads have exceeded Netfiles' limits. You can try again later - the limits are reset every hour - or complete the assignment at an ICS lab.)