## 20101001

### Astronomy quiz question: sidereal motion

Astronomy 210 Quiz 3, Fall Semester 2010
Cuesta College, San Luis Obispo, CA

An observer in San Luis Obispo, CA notices that the constellation Auriga is just above the northeast horizon at 9:00 PM on September 29. (Ignore the fact that your starwheel does not include daylight saving time.) Exactly 24 hours later, this constellation will be __________ the northeast horizon.
(A) slightly lower above.
(B) at exactly the same position above.
(C) slightly higher above.
(D) (None of the above choices, as it would not be visible anywhere in the sky.)

Using a starwheel (planisphere), the position of Auriga will shift slightly the next day, as seen by aligning 9:00 PM with September 29, and then aligning 9:00 PM with September 30, resulting in this constellation being slightly higher above the northeast horizon at the same time the next evening. This is caused by Earth's revolution around the sun while simultaneously rotating about its own axis. Response (B) would be true if Earth did not revolve around the sun, and only rotated about its own axis.

Section 70160
(A) : 4 students
(B) : 12 students
(C) : 23 students
(D) : 1 student

Success level: 59% (including partial credit for multiple-choice)
Discrimination index (Aubrecht & Aubrecht, 1983): 0.68