Monday, March 30, 2009
The king of beasts rules over April's skies
John Goss
John Goss is chairman of the Mid-East Region of the Astronomical League and a former president of the Roanoke Valley Astronomical Society.
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Most constellations don't closely resemble the fanciful figures that they represent. The early evening sky in late March and early April features one that does.
Hanging almost overhead are nine stars that comprise the constellation Leo. If you use a little imagination, you can mentally connect its stellar dots to form the rough outline of a male lion at rest.
One of his front paws is represented by Regulus, which lies almost on the ecliptic. This means that the sun nearly blocks it every year on Aug. 22. On that hot August day, Regulus lies 77 light-years behind the sun, which itself is only eight light-minutes from Earth.
Regulus also marks the bottom of an interesting asterism -- a group of stars not belonging to a single complete constellation -- known by skywatchers as both the "Backwards Question Mark" and the "Sickle of Leo." The descriptive shapes of this asterism form the mane and a forepaw of the lion.
Of the six stars in the Backwards Question Mark, Algieba is the most noticeable other than Regulus. Its brightness closely matches that of the stars of the Big Dipper. Algieba is a stellar giant whose size nearly equals the radius of the orbit of the planet Mercury.
The lion's figure extends eastward ending at Denebola, meaning "tail of the lion." It is one of the closer stars in the sky, shining at just more than 36 light-years away. Besides representing the tip of the lion's tail, it is also the westernmost member of the "Spring Triangle," which includes the bright stars Arcturus and Spica.
This year, Leo contains another object confusing the celestial scene. The planet Saturn, while not as bright as it has been in the past few years, is brighter than any of Leo's stellar members, including Regulus. For the next 12 months or so, Saturn's famous thin ring system slants so that it appears nearly edge-on. As a result, it doesn't reflect much sunlight toward the Earth; therefore, Saturn appears dimmer than in most years.
The moon helps stargazers identify both Regulus and Saturn on two nights in early April. But first, today the thin crescent moon glows softly in the west about 9 p.m. Directly below it floats the Pleiades star cluster. Bring out the binoculars to view this intriguing combination.
Sunday night, the waxing gibbous moon sits just below Regulus at the bottom of the Backwards Question Mark. One night later, it moves beneath Saturn, as it grows fatter and brighter. By the time the moon reaches full, it glides near Spica, the major star in Virgo.
Early morning observers can use the moon to positively identify the two brightest planets. By April 19, the moon arrives in the predawn sky and glows as a thick crescent next to Jupiter. Three mornings later, its thinner crescent shape floats next to bright Venus and above the difficult-to-see Mars.
International Year of Astronomy events
Have you ever seen the moon or Saturn through a telescope? There are several occasions for you to do so this week, weather permitting. In celebration of the International Year of Astronomy, the Roanoke Valley Astronomical Society (www.rvasclub.org) is hosting public observing sessions where people can see the moon's craters and Saturn's rings for themselves.
n Thursday, 6:45-7:45 p.m., "Moon Over the Taubman," near the Taubman Museum of Art; 7:45-9:15 p.m., "Sidewalk Astronomy" in front of Center in the Square.
n Friday, 7:45-9:30 p.m., "Botetourt Skies," International Parkway, Greenfield.
n Saturday, 7:45-9:45 p.m., "Stargazing at the Star," Mill Mountain Star.
n Sunday, 1-2 p.m., "Sun Day on Campus," and 8-9 p.m., "Sidewalk Astronomy," both on the Roanoke College Quad.
