![]() It is located in the first quadrant of the northern hemisphere (NQ1) and can be seen at latitudes between +90° and -35°. Perseus occupies an area of 615 square degrees. The celestial hero Perseus boarders the constellations Aries and Taurus to the south, Auriga to the east, Cassiopeia to the north, and the Andromeda galaxy to the west. Original article on is the 24th largest constellation in the northern sky, named after the Greek mythological hero Perseus. Follow Starry Night on Twitter Follow us Facebook and Google+. This article was provided to by Simulation Curriculum, the leader in space science curriculum solutions and the makers of Starry Night and SkySafari. That’s what makes observing variable stars so absorbing.įor more information on variable stars and detailed charts, visit the website of the American Association of Variable Star Observers. I find SS Cygni one of the most exciting objects in the sky to observe because I never know in advance whether it will be a dim 12th magnitude star or blazing forth at 8th magnitude. ![]() Because they are so close, material passes from one star to the other and periodically ignites, causing the flare-up in brightness. The two stars are less than 100,000 miles apart, orbiting each other in 6.5 hours. ![]() One star is a cool red dwarf the other is a small dense white dwarf. SS Cygni is part of a close binary star system. If you’re really lucky, you can catch it on the rise, and actually observe it brighten in real time. Most of the time it sits down around 12th magnitude, but for a day or two every two months, it pops up to 8th magnitude. It is like a nova in that it undergoes a significant brightening (about 5 magnitudes or 100 times brightness), but it does so at frequent and irregular intervals, roughly every seven to eight weeks. Just as a dwarf planet is not a planet, a dwarf nova is not a nova. SS Cygni is a “dwarf nova” in Cygnus, exploding violently and unpredictably every couple of months. There is a direct relationship between the absolute magnitude of Cepheids and their period, so if you measure the period, you can calculate their brightness, and hence their distance. It is the type star of the “Cepheid” variables which are used as “standard candles” to calculate the distances to globular clusters and nearby galaxies. The cosmic candleĭelta Cephei is perhaps the most famous variable star. You can estimate its brightness on any particular night by comparing it to nearby stars Mirfak (magnitude 1.8), Atik (magnitude 2.8), and Menkib (magnitude 4.0). It varies between magnitude 2.1 and magnitude 3.3, so is easily observable. Yes, its period really is known that precisely.Īlgol is the second brightest star in Perseus. The result is that Algol’s brightness varies by 1.2 magnitudes every 2.86736 days, or 68 hours 48 minutes 59.9 seconds. ![]() As they orbit, each star cuts off the light from the other for a short period. (Image credit: Starry Night software)Īlgol is what is called an "eclipsing variable." It consists of two stars orbiting each other at a close distance, less than 6 million miles (9 million kilometers). Its name means "The Ghoul" in Arabic and it has sometimes been called the "demon star." In early illustrations, it is often depicted as the Gorgon's head in Perseus' hand.Īlgol, the second brightest star in Perseus, is an eclipsing variable: two stars orbiting each other and cutting off each other’s light. Our second star, Algol, has been known to be unusual since ancient times. Its distance is poorly known, but appears to be around 300 light years. Besides changing brightness by 8 magnitudes, it also varies in color, appearing reddest when it is at its dimmest. Mira has a period of 332 days, almost a year in length. That is because these long period variables are all red giant stars, pulsating slowly in the late stages of their development. It is separated by only 2 arc minutes from a 9th magnitude star, but is most noticeable because, like most long-period variable stars, it has a deep red color. (Image credit: Starry Night software)Ĭurrently Mira is around 8th magnitude, so you will need binoculars to see it. Mira, in the constellation Cetus, is the classic long period variable star, slowly pulsing and changing color over a period of nearly a year.
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