Why does the Cepheid "standard candle" have limited usefulness beyond 20 Mpc?
A)Distant galaxies are seen in the past, when Cepheid variables behaved differently than they dotoday.
B)Distant galaxies are so young they do not contain Cepheids.
C)Cepheids are too faint to be seen beyond that distance, even with HST.
D)The light variability of Cepheids diminishes with distance so they do not appear to vary there.
E)Older distant Cepheids are of Population II, where the period-luminosity relation no longerworks.

Question

Quizplus · Accepted Answer

Cepheids are too faint to be seen beyond 20 Mpc with current technology, including the Hubble Space Telescope (HST), limiting their usefulness as standard candles at greater distances.

Why Does the Cepheid "Standard Candle" Have Limited Usefulness Beyond