All around us there are signs of spring. And because of a change in the law several years ago, daylight savings time has kicked in. If you're a frequent reader of Starwatch, you know I'm not a big fan.
The officially start of spring, otherwise known as the Vernal Equinox take place at 5:57 p.m. Thursday. That's when the sun stars start rising and setting above an imaginary line in the sky called the celestial equator, which is a projection in the sky of Earth's terrestrial equator. From now until June 21, the sun will arc higher and higher in the sky.
One fallacy about the Vernal Equinox is that it's the day we have equal amounts of days and night, 12 and 12 hours respectively. That's just not true because of something called astronomical refraction. The shell of atmosphere surrounding our 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. I know that sounds crazy, but that's what happens. If you check the sunrise and sunset times for Thursday, you'll discover the days are already about ten minutes longer than the nights.
So when do the days become equal to nights this time of year? The answer is tomorrow, St. Patrick's Day. Yet another reason to celebrate one of greatest feast days of the year, in my book.
Stars of spring
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. It's one the faintest of 66 constellations through the course of the year.
The Beehive cluster is actually brighter than most of the stars in the constellation. 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 130 BC, 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 more than 3,400 trillion mile away and nearly 60 trillion miles wide.
Get ready for spring, but remember the possible snowfall continues.
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.
(Lynch is an amateur astronomer and author of the book, "Stars, a Month by Month Tour of the Constellations." Contact him at mikewlynch@comcast.net.)