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MCQIntermediateObservational Astronomy & Telescopes
USAAAO — 2023 First Round
Question 2
A cluster has a radius of 2 parsecs. A Sun-like star in the cluster has an apparent magnitude of 10. When we look at the cluster with a telescope that has an en eyepiece with a field of view of 30 degrees, the cluster just fits within the eyepiece. If this telescope has an eyepiece of focal length 20 mm, what is the focal length of its objective lens?
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Source
USAAAO 2023 First Round. Question text, choices, and answer were transcribed from the official USAAAO exam and solutions PDFs.