Over what distance does the Cepheid variable technique work? The faintest objects that can be photographed through the best telescopes have apparent magnitudes of about m = 30. Consider a bright Cepheid with an absolute magnitude of M = -2.4. At what distance could it just be seen?

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Quizplus · Accepted Answer

The Cepheid variable technique is useful for measuring distances up to about 30 megaparsecs (Mpc). The distance modulus equation relates apparent magnitude (m), absolute magnitude (M), and distance (d) as follows: m - M = 5log(d/10). Rearranging this equation to solve for distance gives us d = 10^(m-M+5)/5. Substituting our values gives us d = 30 Mpc.

Over What Distance Does the Cepheid Variable Technique Work? the Faintest