Cepheides in the galaxy M81 - Cepheids in the galaxy M81 - Cepheides are very...

Cepheides in the galaxy M81 - Cepheids in the galaxy M81 - Cepheides are very bright variable stars that serve as cosmic beacons to measure distance from nearby galaxies. Their pulse period is measured and their absolute luminosite is calculated. By comparing the result to their apparent luminosite in the sky, they can be calculated accurately. Here, the space telescope identified cepheides in the M81 galaxy; astronomers were able to deduce a new distance for this galaxy; it would be 11 million years - light from Earth; previous estimates gave a figure of 18 million light years. Image obtained in 1993. Astronomers have discovered variable stars in the spiral galaxy M81, and measured the distance of the galaxy to be 11 million light - years (3.4 megaparsecs). They quote a 10% uncertainty in this result (plus or minus approximately one million light - years). Previous estimates of the galaxy's distance have ranged from 4.5 to 18 million light - years (1.4 to 5.6 megaparsecs). The astronomers used the Hubble '5 Wide Field & Planetary Camera to study two fields in M81. In each field they took 22 twenty - minute exposures spread over 14 months to find the variable stars and measure their periods and brightness. Cepheids are pulsating stars that become alternately brighter and fainter with periods ranging from 10 to 50 days. Astronomers have known for over 50 years that the periods of these stars precisely predict their total luminous power, which allows their distance to be measured. Messier 81 is a large spiral galaxy in the constellation Ursa Major. It is a rotating system of gas and stars similar to our own Galaxy, the Milky Way, but approximately twice as massive. This galaxy achieved prominence three months ago when the brightest northern supernova this century was discovered. In the expanding universe, the Hubble Constant (H0) is the ratio of the rec