Is it any wonder that most avid stargazers hate Daylight Saving Time? When DST ends on November 4, we can get a decent view of the night and still get to bed at a reasonable hour.
November 4! I’m not much of a conspiracy theorist, but does anybody remember when DST was just a summer thing? It seems like over the years Eastern Standard Time has shrunk to just a few months. SST is now the exception, not the rule.
Does Congress really have the right to tell us what time it is, and why does it keep changing its collective mind?
God bless EDT. By 7:30 p.m. blessed darkness will have fallen. The constellation Perseus rises beautifully in the northeast about half way up to the top of the sky. The brightest stars of the ancient Greek hero form an upside-down “Y.”
Here, my well-rested stargazing friends, there is much to see.
Start from the brightest star of the constellation, located at the center of the “Y.” The star Mirphak gets its name from the old Arab stargazers, who mapped the sky with great precision. Mirphak is a shortened version of Mirphak al Thurayya, the “Elbow Nearest the Many Little Ones.”
“Little Ones” there are aplenty near Mirphak. Look at the area with binoculars and you will discover the dozens of stars in the “Perseus Association,” which provides one of the best “bino” views in the sky.
Mirphak is relatively distant from Earth for a naked-eye star at something like 620 light years away. To be so bright, it must be powerful, producing 4,000 times the energy output of our puny daytime star, the sun.
Up and to the right from Mirphak is M34, visible in a small fuzzy patch in binoculars. In a small telescope, it will resolve into a few dozen stars. M34 is a star cluster, a group of gravitationally bound stars traveling together in space.
The real “star” of Perseus is Algol, the Demon’s Head. Find it by looking to the right and slightly down from Mirphak.
Algol has a long and storied history. From early times, it has represented the head of the snaked-haired Medusa, which Perseus holds, newly severed, in his hand. One look at her face turned the unfortunate viewer to stone, so don’t look at Algol too long.
Sometime before 1672, the Italian astronomer Geminiano Montanari noticed that Algol was not steady in its brightness. From 1782–83, British astronomer John Goodricke carefully studied the varying brightness of the star and noticed that it faded from bright to dark and back again over a period of two days, 20 hours, and 40 minutes. Every 2.87 days, Algol dims abruptly for about 10 hours.
Algol was thus the first “variable” star to be discovered and measured accurately.
Goodricke suggested that Algol was really two stars. A small, bright primary star has a dimmer, larger star in orbit around it. As the dimmer star passes in front of the brighter one, the light from the brighter star is filtered through the dimmer one. As a result, the bright star dims abruptly. Such stars came to be called eclipsing binaries.
The greatest astronomer of Goodricke’s age, William Herschel, rejected the idea. He couldn’t see the second star in his telescope. Later, Herschel discovered other stars that had companions in orbit around them. He changed his mind and accepted Goodricke’s findings wholeheartedly, even though Agol’s companion is too faint and too close to Algol to be seen in a telescope.
You can observe the dimming of Algol yourself by using an old stargazer’s trick. Variable-star observers measure the changing brightness of a star by comparing it night after night with the brightness of a star that doesn’t vary.
The perfect star for that purpose is called Delta, down and to the left of Mirphak. Most of the time, Algol will look brighter than Delta. When Algol is in eclipse, it will look about as bright as (or even a tiny bit dimmer than) Delta.
It might take several nights of observing to see the change, but it’s worth the wait. The Demon’s Head has winked at you from the deep recesses of space. Don’t forget to wink back.
Tom Burns is the director of Perkins Observatory. He can be reached at firstname.lastname@example.org.