![]() ![]() ![]() The phase of each image is indicated at the lower left. Because some phases are poorly covered, B jumps at some points along its path. This animation was assembled from 55 images of the CHARA interferometer in the near-infrared H-band, sorted according to orbital phase. The eclipsing binary pair is separated by only 0.062 astronomical units (AU) from each other, so close in fact that Algol A is slowly consuming the less massive Algol B by continually stripping off Algol B’s outer layers. Enjoy brilliant planet Jupiter, which dominates the eastern sky in the evening.Algol (β Persei) is a triple-star system (Algol A, B, and C) in the constellation Perseus, in which the large and bright primary Algol A is regularly eclipsed by the dimmer Algol B every 2.87 days. Albeiro is a beautiful gold and blue pair in a small telescope even at low magnification such as 40x.įirst-quarter moon is on Oct. Binoculars mounted on a tripod or held firmly against a support, may begin to show its double nature. Another easy-to-see double is Albeiro, Beta Cygni, visible high in the south on October evenings. If you have a telescope magnifying about 100x, you should be able to quickly tell the star is double, the two stars apparently hugging each other. In other words, Algol’s starlight you see tonight (in 2010) left the star during the First World War.Īlthough a small telescope won’t show Algol as two or three separate stars, there are many double or multiple star systems you can see.Ī short hop away from Algol is a bright star, Gamma Andromedae. This impressed her and the two were married and lived happily ever after.Īlgol is 92.8 light years away that’s how many years it takes the light to reach us. He held this up to destroy a sea monster that was threatening Andromeda. Perseus had already cut off the monster Medusa’s head, which is represented by Algol. In Greek mythology, Perseus was a hero who rescued the maiden Andromeda, daughter of King Cepheus and Queen Cassiopeia. The third Algol star is on average, 2.69 AU from the central star Beta Persei A and takes 1.86 years to go around without ever eclipsing anything as seen from Earth.Īn Italian astronomer, Geminiano Montanari, first noticed the variability of Algol in 1667, though probably it was known for a very long time before that by sharp-eyed observers. That seems like a lot to us, but consider that our innermost planet, Mercury, averages 36 million miles away from the sun, and the Ssun is almost a million miles across (864,000 miles). Beta Persei A and B are thus 5,766,000 miles apart. One astronomical unit is the average distance between the Earth and sun, or 93 million miles. That’s another way distance is measured within solar systems. Too bad.Ī and B are separated by only 0.062 astronomical units (AU). Nevertheless, more fun names don’t seem to slip in official classifications. Maybe you can apply a better trio of names, such as Huey, Dewey and Looie. There are actually three stars in the system the brightest is referred to as Beta Persei A the star that eclipses it from our line of sight is Beta Persei B the other is Beta Persei C. The star is also referred to as Beta Persei. Once you find the constellation with a star map, you can compare Algol with nearby stars to estimate its brightness. Algol is one of the brighter stars of the constellation Perseus. Look for Algol in the northeast, below the W-shaped constellation Cassiopeia. (For comparison, the stars of the Big Dipper are also 2nd and 3rd magnitude.) Usually shining at a near constant magnitude +2.1, it dips to +3.4 every two days, 20 hours and 49 minutes. Unlike other variables where the change is due to pulsations within the star, the reason for the wink is its companion star.Īlgol has another, dimmer star in a tight orbit, which like clockwork partially eclipses Algol. You can easily watch it change light over several nights. Some rise from seeming insignificance requiring a good telescope to easy visibility with just your pearly whites.Īlgol is a famous variable star of the evening autumn sky. There are numerous types of variable stars most change on a fairly regular basis, over a predictable length of time and range of magnitude. There are thousands of stars you can see that vary in brightness. The next clear night be sure to look up the star that winks back. ![]()
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