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This month we celebrate the Vernal Equinox (when the sun crosses the Equator on its annual visit to the north and day and night are of equal duration) and the March sky is dominated by brilliant constellations such as Orion. This month also provides an excellent opportunity for our readers to extend his or her observations to a particularly interesting sight: Algol.
Throughout the month of March, Algol is nearly overhead at sunset and is visible the entire evening. This star is easy to overlook because it's not nearly as bright as some stars in the night sky, but it is Algol's brightness that makes it so unusual and fascinating. You see, Algol's brightness changes, making it a so called "variable star." There are many different reasons for a star to change its brightness. Some stars change due to an intrinsic property of their complicated astrophysics. Other stars change brightness because they are regularly eclipsed by a darker companion orbiting around it. Algol is of the latter type - an eclipsing variable.
The star we see as Algol is actually the brighter of the two stars, so technically we should call it "Algol A." It has a magnitude of 2.1. That's fairly bright. In fact, Algol A is about 100 times as bright as our Sun, but it's much further away. Orbiting Algol A, like a planet, is Algol B, a very dim star. Fortunately for the amateur astronomers of Earth, the plane of Algol B's orbit is along our line of sight. That means Algol B passes in front of Algol A during its orbit. As it does so, Algol B eclipses Algol A, blocking most of the light from the brighter star. During this eclipse Algol dims from a magnitude of 2.1 to 3.4.
This is a fascinating event to watch but, of course, the first thing you have to do is find Algol. These directions will help you. (It's not easy.)
Imagine a line from the very bright star Capella to the (not quite so) bright stars of Almaak, Mirach and Alpheratz. There is a star on either side of the line between Almaak and Capella, about midway between them. The one to the north is Mirphak, but the one to the south is our target- Algol. (Don't confuse it with the brighter star Hamal, and don't confuse any of these with Saturn and Jupiter which would be visible farther south than these stars!)
One effect of the equinox is that early in the morning of March 28th the British will move their clocks forward an hour as they begin British Summer Time (BST). This is nothing more than manipulation of clocks, and the point of BST is to maximize use of daylight hours as the days get longer. At least that's the excuse. You may be wondering, "So what?" Well, this historical and political fiddling with the clocks causes a great deal of confusion for people like us who want to follow "nature's time." Astronomers and navigators use Universal Time (UT), which used to be called Greenwich Mean Time (GMT). Although in the winter UT is the same as BST, during "Summer Time" it's an hour later.
Folks in North America will do the same "clock magic" a week later on April 4th. (Britain is at a higher latitude than most of the US so the Brits like to switch earlier to get the most use of their longer days.) So the Brits set their clocks ahead a week before the Americans. And Bonaire uses Atlantic Standard Time (UT minus 4 hours) and never changes it with the season.
The end result is that for a week nobody has a clue what time it is!! Well, it isn't quite that bad, but it is very confusing. G.D. and Dr Jamie Love
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