Type I Cepheids

Type I Cepheids are a class of pulsating stars that regularly expand and contract, causing their brightness to vary in a predictable cycle. They are more massive, younger, and found primarily in the spiral arms of galaxies with lots of gas and dust. Their pulsation periods are directly related to their intrinsic brightness, making them valuable cosmic distance markers. By measuring their brightness and pulsation period, astronomers can determine how far away they are, helping to map the scale of the universe with high accuracy.