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Astronomy From Your Back Yard - 3/2 to 3/8 2011

By Dave Grosvold

  
The New Moon occurs this week on Friday morning at 2:47 AM CST. Last week we watched the waning crescent moon rise in the eastern sky in the pre-dawn hours, while late this week and early next, we will begin to catch the newly waxing crescent in the western sky starting early Sunday evening. Between now and then, we will be treated to our best dark skies while the Moon is making its monthly pass near the Sun.

  
  
Sirius (α Canis Majoris) shines high in the south during the early evenings in early March. Sirius is the brightest star in our sky at magnitude -1.46. Sirius is known as the Dog Star, due to its position of prominence in the constellation Canis Major, and is actually a binary star system. Sirius A, the larger component, is a white main-sequence star, while Sirius B is its white dwarf companion.

Sirius marks the bottom apex of the Winter Triangle asterism, which is now directly south of us in early evening. The other two vertices of the Winter Triangle are Procyon (α Canis Minoris,) in Canis Minor, and Betelgeuse (α Orionis) in Orion. Over the course of the month of March, we will see the Winter Triangle appear to move further west each evening if you look at about the same hour of darkness. Don't forget — we switch to Daylight Saving Time on March 13, so the same hour of darkness occurs about an hour and a half later by the end of the month. So if you look at 7:30 PM tomorrow evening, by the end of the month it will be about 9:00 PM before you will see the sky reach the same darkness level.

Jupiter is sinking down the western sky this week, just a bit lower each day. By Tuesday evening early next week, Jupiter sets by 8:00 PM CST, so early evening is the best time to catch it. Still brighter than Sirius by quite a bit at magnitude -2.1, it is not nearly as bright as it was in late December. In the meantime, Venus at magnitude -4.1 is almost twice as bright, rising in the east-southeast before dawn this time of year. Since they are not both in the sky together, it is difficult to compare the two without instrumentation.

On Sunday evening, look low in the western sky for a very thin waxing crescent Moon almost due west, about 6° to the right and slightly higher than mighty Jupiter (6 degrees would be about 4 finger widths at arm's length.)

  
Starting early next week, Mercury is a challenging evening object, and is now very low in bright twilight below Jupiter. Starting Monday, very early in the twilight (about 6:15 PM CST,) if you have a very clear sky and you can find an observing location with a low, clear western horizon (like the eastern shore of a lake,) Look close to the horizon with a pair of binoculars directly below the now-thicker waxing crescent Moon and you may find Mercury as a tiny pin-prick of bright light against the glowing sunset background. Mercury will set between 6:30 PM and 6:45 PM CST, so you don't have a lot of time to look. The visibility of objects in bright twilight is greatly exaggerated in the accompanying image, but you get the idea.

Saturn rises in Virgo around 8 PM CST, but it's best to wait to observe it with a telescope until it gains high altitude, clearing the bad seeing due to the thicker atmosphere at the horizon. Saturn is highest in the south around 2 AM CST. Spica (α Virginis,) slightly fainter, shines about 9° below Saturn all evening and into the early morning hours. Saturn's rings are tilted at about 9.7° with respect to Earth right now, so they should easily be visible in small telescopes. Look for Saturn's moons while you have it centered in your eyepiece.

The International Space Station (ISS) will make several bright passes over our area early next week. Look for the ISS to pass low in the NE (from the NNE to the NE) at an altitude of 10° at 7:05 PM CST on Sunday. This pass will be at magnitude -1.0, which is about the same as Regulus in Leo. On Monday evening, the ISS passes over our northern sky at an altitude of 25° at 7:31 PM CST. This time, it will reach magnitude -2.3, or slightly brighter that Venus. Then Tuesday evening, the ISS passes high over our northwestern sky at 7:56 PM, reaching an altitude of 50° and a magnitude of -2.8, which will be brighter than anything else in the sky at that hour.
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