Author Question: Suppose an elliptical galaxy is so far away that we cannot see even its brightest stars ... (Read 47 times)

mwit1967 · **on:** Jul 27, 2018

Suppose an elliptical galaxy is so far away that we cannot see even its brightest stars individually. Which of the following techniques might allow us to measure its distance?

A) We could use parallax.
B) We could use Cepheid variables as standard candles.
C) We could use a white dwarf supernova as a standard candle.
D) We could use radar ranging.

Question 2

Why does the Cepheid standard candle have limited usefulness beyond 100 Mpc?

A) Distant galaxies are seen in the past, when Cepheid variables behaved differently than they do today.
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 longer works.