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The Sky This Week, 2013 March 12 - 19

Say hello to Comet Pan-STARRS!

Comet C/2011 L4 (Pan-STARRS), 2012 March 12, 02:22 UT
Imaged at the US Naval Observatory Flagstaff Station, Flagstaff, AZ by Dr. Marc Murison
with a Canon PowerShot SX230 HS digital camera, 5s @ f/5.0, ISO 100, EFL ~38mm

The Moon waxes in the evening sky this week, reaching First Quarter on the 19th at 1:27 pm Eastern Daylight Time. Try to spot her very slender crescent shortly after sunset on the 12th. Each succeeding night she climbs higher in the sky, encountering bright Jupiter on the evening of the 17th. She finishes the week high above the stars of Orion, the Hunter.

Keep your eyes peeled this week for a visitor from the outer solar system. Comet C/2011 L4 (Pan-STARRS) will be swinging into the early evening sky, hopefully becoming visible by the end of evening nautical twilight (about an hour after local sunset). Named for the Panoramic Survey Telescope and Rapid Response System, a program largely funded by the Air Force Research Laboratory to detect potentially hazardous Near-Earth Asteroids, it has been putting on a good show for our friends in the Southern Hemisphere. Discovered at the Pan-STARRS facility on Haleakala, Hawai'i in June, 2011, the comet passed perihelion on March 10. Unfortunately for us it will not be visible against a dark sky, but folks with a low, flat western horizon should have a decent whack at it in fading evening twilight. Those of us in the DC area should get our first good chance to spot it on the evening of the 12th, when it will be about five degrees to the "left" of the very thin crescent Moon. Use binoculars to look for the comet, which will appear as a diffuse swatch of light. You may even see a tail pointing upward from the horizon as the sky continues to darken. On each succeeding evening the comet should be a little bit higher as it slowly drifts northward against the horizon. It currently shines at second magnitude so if the sky is exceptionally clear you may be able to spot it with the unaided eye. If you have a digital camera and a tripod you can try your hand at capturing an image. Point your camera due west between 45 minutes to an hour after sunset. Use manual settings to set the focus at infinity and try a shutter speed of about 5 seconds at f/5.6 with an ISO rating of 100 to 400. Use the time-delay function to release the shutter, and bracket your images with different exposure times. Take lots of images; photons are free!

Later in the evening take a few minutes to enjoy the bright stars of the Great Winter Circle as they grace the darkening sky. By the end of evening twilight you’ll find Orion west of the meridian as his faithful dog Canis Major crests the southern horizon. Sirius, the brightest star in the sky, marks this constellation and culminates as full darkness falls. Sirius is one of the closest stars to the solar system, just over eight light-years away. It was one of the first stars to have a companion detected by variations in its proper motion through space. This companion, the first "white dwarf" star to be discovered, was found by the American optician Alvan Graham Clark while testing an 18.5-inch telescope lens in January 1862. Sirius is one of my favorite stars to observe with the naked eye. Turbulence in our atmosphere, especially after the passage of a strong cold front, causes the star to "twinkle" furiously, often rapidly cycling through all the colors of the visible spectrum in addition to its usual steady blue tint.

Jupiter continues to grace the early evening sky. Daylight time has given the giant planet another few weeks of good observing time before he slips into the turbulent air above the western horizon. You can still easily spot his four bright moons, discovered by Galileo in 1610, with binoculars or a small telescope, and larger instruments will give a fine view of his more prominent cloud bands. Point a four-inch or larger telescope at him at around 8:30 pm EDT on the 13th or the 18th and you should be able to glimpse the famous Great Red Spot, an Earth-sized storm in the planet’s atmosphere that has persisted for over three centuries!

Saturn once again waits in the wings for Jupiter to exit the starry stage. By the time Old Jove sets at around 1:00 am, Saturn is climbing higher in the southeast. Night owls will be rewarded with the sublime view of the cream-colored planet set among his spectacular rings, and owners of six-inch or larger scopes can find the planet nestled among half a dozen of its many small, icy moons. If you’re up before the Sun, try to catch Saturn then. He’ll be just past the meridian in the south, but the morning air will usually provide ideal stillness to probe his finer details.

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