ASTRONOMY FUNDAMENTALS - Chapter 9, Exercise 1 Solution
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Identifying a Detection Method from Its Observation

PROBLEM
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A team reports observing a star's brightness drop by a small,
consistent amount every 12 days, then return to normal. Identify which
detection method this team is using, and explain what real physical
event is causing the observed dimming.

SOLUTION
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The observation described - a periodic, repeating drop in a star's own
measured brightness, followed by a return to normal - matches the
chapter's own real description of the TRANSIT METHOD, the same
technique used by NASA's Kepler space telescope.

The real physical event causing this dimming is a planet passing
directly in front of its own host star, from Earth's specific point of
view. As the planet crosses (transits) the star's disk, it blocks a
small, consistent fraction of the star's own light, causing the
measured brightness to dip. Once the planet finishes crossing, the
star's brightness returns to its normal level - until the planet
completes another full orbit and transits again, which is exactly why
the dimming repeats on a consistent, periodic 12-day cycle. That
12-day period is itself real, useful data: it directly reveals the
planet's own orbital period.

ANSWER: This is the transit method. The dimming is caused by a planet
passing in front of its host star as seen from Earth, with the
planet's own real orbital period being 12 days.

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WHY THIS WORKS AS AN ANSWER

The chapter draws a clear real distinction between its two detection
methods: radial velocity detects a star's own motion (a Doppler shift
in its spectrum), while the transit method detects a star's own
brightness changing. Since this problem describes a brightness change,
not a motion or spectral shift, transit is the only one of the two real
methods that actually fits the described observation. The periodic,
repeating nature of the dimming - rather than a one-time event - is
also a key real clue, since it reflects the planet's own real,
repeating orbital motion around its star.