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The Sky This Week, 2013 March 19 - 26

A Paschal Moon, Planets, and Pan-STARRS to enjoy on the equinox.

 Comet C/2011 L4 (Pan-STARRS), imaged 2013 March 12 by Rich Schmidt
Image made with a DSLR camera and a 400mm telephoto lens from the
dome of the 12-inch telescope at the USNO, Washington, DC

The Moon brightens the evening sky this week, wending her way across the sky from the stars of winter to the rising constellations of spring. Full Moon occurs on the 27th at 5:27 am Eastern Daylight Time. In popular folklore this Full Moon goes by a variety of names since it occurs close to the time of the vernal equinox. Among the more common appellations are the Crow Moon, Sugar Moon, Sap Moon, Worm Moon, and Lenten Moon. In the Judeo-Christian faiths this is the Paschal Moon, which fixes the dates of two of the most important dates in religious calendars, Passover and Easter. Luna begins the week high above the bright stars of Orion. On the evenings of the 23rd and 24th see if you can spot the bright star Regulus near her bright glare. The first few nights of the week are great times to turn the telescope toward Luna’s battered and barren face. She’s high in the sky and her phase changes over the next several nights reveal some of her most famous features. It’s a great time to become familiar with many of these popular landmarks on our only natural satellite.

The vernal equinox falls on the 20th at 7:02 am EDT. Since sunrise is only nine minutes later here in Washington we should see the center of Old Sol’s disc aligned due east as he pops into the morning sky. This equinox is probably the most important seasonal marker in the calendar since it heralds the season of birth and renewal. In addition to the various religious connections to the date it also used to mark the beginning of new years in many civil calendars. The English calendar observed the new year on March 25 until finally adopting the Gregorian calendar in 1752. In any case, the Sun’s declination will now remain north of the celestial equator until the autumnal equinox, which falls this year on September 22nd.

Comet C/2011 L4 (Pan-STARRS) should still be visible in fading evening twilight this week. From about 45 minutes to an hour after sunset you should be able to spot this visitor from the outer solar system a little bit north of due west about 10 degrees above the horizon. It should be an easy sight in binoculars, looking very similar to the many images you’ve probably seen of it. It has apparently been running a bit brighter than initial predictions, and many observers with clear western views have reported seeing it with the naked eye. During the course of the week it will slowly gain altitude as it drifts to the north, but it will also probably start to fade. However, it should remain it should remain visible for at least another week or two before it fades into the deepening twilight.

Mighty Jupiter is still the brightest object after the Moon in the early evening sky. The giant planet now spends the evening hours in the western half of the heavens where he is visible until around midnight. After the Moon, Jupiter is the next best target for your small telescope, but be prepared for something of a shock. After looking at the expanses of the Moon’s dusty plains and battered crater ranges Jupiter presents a very small disc for scrutiny. However, in moments of steady air an increase in magnification will begin to bring out subtle details. Also, his four bright Galilean moons should be easy to spot. Although they appear as star-like dots of light, each of them is comparable to or larger than our Moon. Keep that in mind for a sense of scale!

Saturn now rises at around 10:30 pm. By the time Jupiter sets the ringed planet is high enough in the southeast to catch a quick telescopic glimpse before retiring for the night. Saturn’s disc is about half the size of Jupiter’s but the planet also sports his extraordinary rings, which almost double the apparent width in the eyepiece. We now know, thanks to the Cassini orbiter probe, that the rings consist of billions of icy bodies in independent orbits around the ball of the planet. These bodies are influenced by the gravity of Saturn itself and the swarms of small moons orbiting nearby. Pictures from Cassini show thousands of "ringlets" orbiting in the rings themselves with small "gaps" of less material in between. One large gap, known as Cassini’s Division, is visible in earthbound telescopes as a thin black line about one third the distance in from the rings’ edges. You should be able to see it on a night with steady air.

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