Measuring Distances in Space
Cepheid variable stars are one of the standard candles of the universe. Standard candles are objects of either known brightness or predictable behaviour that astronomers can use to determine distance. Cepheid variable stars are unstable, yellow supergiant stars that are about 1000 times brighter than our Sun and that pulse, or change in size and brightness. The large, bright Cepheids pulse more slowly than the smaller, dimmer Cepheids.
Astronomers can use the connection between the rate of a Cepheid’s pulse and its brightness, or absolute magnitude, as a measure of its distance
from Earth.Absolute magnitude is the actual amount of light the star gives off, recorded at a standard distance. To determine distance, astronomers
compare the Cepheid’s absolute magnitude with its apparent magnitude. The apparent magnitude is the brightness of a star as it appears in the night sky. Therefore, when astronomers compare the absolute magnitude of the Cepheid with its apparent magnitude, they can calculate its distance from Earth because light fades with increasing distance from the observer. Fortunately, Cepheid variable stars are found in most galaxies.
What are Cepheid Variables?
The red shift of a galaxy is another way that astronomers determine distance. Recall from Section 13.1 in the Science Probe 9 textbook that the farther an object’s spectral lines are shifted to the red end of the spectrum, the faster the object is moving away from Earth. Therefore, the more distant it must be as well. This connection is a direct result of our expanding universe. Red shift is a very useful way to measure distances to even the most remote galaxies.
What is the Red Shift?
