This is Dudley Observatory’s Skywatch Line for Friday, March 15 through Sunday, March 17, written by Sam Salem.
On Friday, the Sun rises at 7:08am and sets at 7:02pm; the waxing gibbous Moon rises at 12:45pm and sets at 3:14am. As darkness falls on Friday and Saturday, let the waxing gibbous Moon guide you to the constellation Gemini’s two brightest stars, Castor and Pollux, to the north of the Moon. Then, look to the south of the Moon for the bright star Procyon, also known as the Little Dog Star, the brightest star in the constellation Canis Minor the Lesser Dog. You should be able to see these three bright stars, even in moonlit glare. Castor, Pollux and Procyon outline the eastern border of a large asterism, or noticeable pattern of stars, called the Winter Circle, or sometimes the Winter Hexagon. Rigel, Aldebaran, Capella, Procyon, Sirius, Castor, and Pollux are the bright stars that make up the large, circular pattern. Procyon also marks the eastern terminus of a secondary pattern within the Winter Circle, called the Winter Triangle. An imaginary line, or arc, drawn from Procyon and passing in between the Gemini stars directs you to Polaris, the North Star.
Mars shines at 1.3-magnitude, in southern constellation Aries at dusk. Mars sets at around 11:45pm. Jupiter rises in the east-southeast around 2:20am. Shining at magnitude –2.1, Jupiter resides in the non-zodiacal constellation of Ophiuchus. The best time to view Jupiter in a telescope is around 45 minutes before sunrise, when the planet has climbed to an altitude of 20 degrees. At that same time, Jupiter shares the southeast sky with Saturn and Venus. Saturn is a magnitude 0.6 dot rising a few minutes after 4am. Venus rises around 5:38am, gleaming at magnitude –4.0. Viewing prospects for Jupiter and Saturn are improving week after week, while Venus is very gradually losing ground. Venus will adorn the dawn until mid-summer.
Nights over this waxing gibbous Moon weekend are good time for some Moon gazing. Copernicus is a large complex crater. Though Copernicus is an impressive 93 kilometers across, like most big craters, it’s surprisingly shallow, only 3.7 km deep. Terraced walls are another feature of large complex craters. In a scope you can see that Copernicus’s inner walls don’t slope smoothly to its floor, rather, they exhibit a stair-step appearance. Try to make out the rows of secondary craters pockmarking the area surrounding Copernicus. These secondary craters are small impacts created by debris thrown out by the initial impact that excavated the main crater. You can see a particularly prominent string of secondary craters about one crater diameter northeast, or upper right, of Copernicus. When the Moon is a fat gibbous phase or full, the rays emanating from Copernicus dominate the region. But if you look carefully, you’ll notice that the rays aren’t as bright or well defined as those belonging to the Moon’s most magnificent ray crater, Tycho. This could be seen as a clue to the relative ages of these objects. Copernicus’s rays aren’t as well preserved because they’re nearly a billion years older than those adorning Tycho. Use a lunar chart to guide you to the Moon features.
Saturday marks the 269th. birthday of Caroline Lucretia Herschel. The German-born British astronomer, sister of Sir William Herschel, who assisted in his astronomical researches making calculations associated with his studies. In her own telescope observations, she found three nebulae in 1783 and eight comets from 1786 to 1797. In 1787, King George III gave Caroline a salary of 50 pounds per year as assistant to William. She published the Index to Flamsteed’s Observations of the Fixed Stars and a list of mistakes in 1797.