20141005

Astronomy quiz question: Balloon Experimental Twin Telescope for Infrared Interferometry (BETTII)

Astronomy 210 Quiz 3, fall semester 2014
Cuesta College, San Luis Obispo, CA

"BETTII3_low.jpg"
NASA Goddard Space Flight Center
http://asd.gsfc.nasa.gov/bettii/

The two far-infrared reflector telescopes of the Balloon Experimental Twin Telescope for Infrared Interferometry (BETTII)[*] have the same 0.50 m (1.6 ft) diameter, and are separated by a distance of 8.0 m (26 ft) between them. This telescope system is attached to a balloon that ascends to an altitude of 40 km (25 miles) in the upper atmosphere.[**] If the two mirrors of this telescope system were instead combined into a single mirror with the same total surface area, the resolving power would:
(A) decrease.
(B) remain the same.
(C) increase.
(D) (The telescope would no longer be able to function.)

[*] S. A. Rinehart ; R. B. Barclay ; R. K. Barry ; D. J. Benford ; P. C. Calhoun, et al., "Design and status of the Balloon Experimental Twin Telescope for infrared interferometry (BETTII): an interferometer at the edge of space," Proc. SPIE 8445, Optical and Infrared Interferometry III, 844508 (September 12, 2012), http://dx.doi.org/10.1117/12.926376.
[**] http://asd.gsfc.nasa.gov/bettii/.

Correct answer (highlight to unhide): (A)

Increasing the distance between telescopes creates a much larger effective diameter to increase resolving power. Thus decreasing this separation distance would decrease resolving power.

Section 70158
Exam code: quiz03s8tE
(A) : 27 students
(B) : 8 students
(C) : 5 students
(D) : 0 students
(No response: 1 student)

Success level: 66% (including partial credit for multiple-choice)
Discrimination index (Aubrecht & Aubrecht, 1983): 0.45

Section 70160
Exam code: quiz03n6n4
(A) : 24 students
(B) : 7 students
(C) : 4 students
(D) : 0 students

Success level: 72% (including partial credit for multiple-choice)
Discrimination index (Aubrecht & Aubrecht, 1983): 0.60

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