Daylight savings time has kicked in, and if you’re a frequent reader of Starwatch you know I’m not a big fan of it.
The official start of spring, otherwise known as the Vernal Equinox, take place at 2:57 p.m. Thursday. That’s when the sun starts rising and setting above an imaginary line in the sky called the celestial equator. From now until June 21st the sun will arc higher and higher in the sky.
One fallacy about the Vernal Equinox is that that’s the day that we have equal amounts of days and night. That’s not true, due to something called astronomical refraction. The shell of atmosphere surrounding Earth bends the light coming from the sun, or any other celestial object for that matter. The maximum effect of the bending of light is along the horizon, where from the perspective of the observer the atmosphere is the thickest. Believe it or not, when the sun appears to be right at the horizon it’s actually below the horizon. So when the sun is setting it’s actually been below the horizon for about five minutes. Conversely in the morning the sun may appear to be just above the horizon when it’s actually still below the horizon. If you check the sunrise and sunset times for this Thursday you’ll discover that on that day the days are already about 10 minutes longer than the nights.
So when do the days become equal to nights this time of year? The answer is Monday, which is St. Patrick’s Day. Yet another reason to celebrate one of greatest feast days of the year, in my book.
In the night sky this time of year one of my favorite signs is the appearance of the bright star Arcturus. It’s the second brightest nighttime star and when you start to see it rising in the northeast by around 9:30 to 10 p.m., spring is right around the corner.
Another celestial sign of spring is the Beehive star cluster, located in the very faint constellation Cancer the Crab. Don’t bother trying to find this constellation, though. Instead, look in the high southeastern sky about halfway between the brighter constellations Leo the Lion and Gemini the Twins.
If it’s dark enough where you are, the Beehive cluster, known astronomically as Messier object or M-44, looks like a faint patchy cloud. When ancient Greek astronomers like Hipparchus observed it around 130BC, he registered it in his star catalogue as a “cloudy star”. The Romans saw it as a manger and called it Praesepe, which is Latin for manger.
In the early 1600s when Galileo poked his telescope toward the Praesepe and saw it as a cluster of stars it eventually got the name Beehive cluster. With your not so crude telescope, or even a decent pair of binoculars, you can easily see how it got that moniker.
Astronomically the Beehive is considered an open star cluster, a group of young stars that emerged out of the same hydrogen gas nebula. The stars in this cluster are believed by astronomers to be about 600 million old, and while that’s considered a young age for a star, is rather old a cluster of young stars. Many of these same kinds of clusters are gravitationally broken up before the time the stars are that old, but the Beehive is hanging in there. That “teenage mob” of at least 200 stars is over 3400 trillion mile away and nearly 60 trillion miles wide.
CELESTIAL HUGGING THIS WEEK: The waning gibbous moon passes by the planet Mars and Saturn this week. Best seen in the low south to southwest sky in the early morning twilight sky…See the diagram.
Mike Lynch is an amateur astronomer and professional broadcast meteorologist.
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