The absolute magnitude of a star is a measure of its intrinsic brightness, or the amount of light it emits. By calculating absolute magnitudes for Cepheids, we can determine their true luminosities and use them as standard candles to measure distances in the universe.
Absolute magnitudes for Cepheids are calculated using a formula that takes into account the star's period of variability and its apparent magnitude, or the brightness as seen from Earth. This formula, known as the period-luminosity relation, was first derived by astronomer Henrietta Swan Leavitt in the early 20th century.
Cepheids are important in astronomy because of their predictable and regular pulsations, which make them reliable standard candles for measuring distances in the universe. They have been used to determine the distances to nearby galaxies and have played a crucial role in the development of the cosmic distance ladder.
By using Cepheid variables as standard candles and measuring their apparent and absolute magnitudes, we can calculate the distance to objects in the universe. This allows us to create a three-dimensional map of the universe and estimate its size and expansion.
While Cepheid variables are reliable standard candles for measuring distances up to a certain point, they do have limitations. Their period-luminosity relation breaks down at very high luminosities, and they are not as useful for measuring distances beyond a certain distance. In these cases, other standard candles such as supernovae or the cosmic microwave background radiation are used.