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Astronomy From Your Back Yard - 2/16 to 2/22 2011

By Dave Grosvold

  
Aurora over Fairbanks, Alaska, October 26, 2007
Photo by Mila Zinkova
Unfortunately, the chances are much lower for seeing the Aurora Borealis or "northern lights" than were reported earlier. The recent coronal mass ejection (CME, or solar flare) from Sunspot 1158 will hitting our planet's magnetic field for the next 24 - 48 hours. The chances of seeing an aurora at high latitudes (50°N,) are now down to 45%, with much slimmer chances (less than 5%,) that they will reach as low as 35°N, the latitude of NW Arkansas. There will be more chances over the next few years though as the number of CMEs is now on the increase.

  
NASA Photo
However, for another unusual treat, sky observers stand a good chance of viewing the Zodiacal Light from Fort Smith and NW Arkansas during the last half of this month. Starting on Saturday evening, find a dark sky location with a clear western horizon, wait for your eyes to dark-adapt, and be prepared to start looking west along the horizon about an hour and a half after sunset. If the zodiacal light is visible, you will see a vague, huge pyramid of softly glowing light sloping toward the south along the line of the ecliptic. Don't give up if you don't see it the first time you go out. This phenomenon will occur in the evenings from Saturday over the next 10 days or so.

  
On Thursday evening, look to the left or lower left of the Moon after dark for Regulus. Farther left of them is Gamma Leonis, not much fainter than Regulus. Look farther to the Moon's lower right for orange Alphard.

The Full Moon occurs this week at 2:36 AM CST Friday morning. On Friday evening, look for Regulus about a fist-width above the Moon. Regulus marks the bottom-right end of the Sickle (actually the bottom of the Sickle's handle.) The Sickle is an asterism in the constellation Leo. Also on Friday evening, at 6:20 PM CST, look straight to the north toward Polaris to catch Iridium 13 as it flares to an intensely bright magnitude -8.0.

At dusk this week, Jupiter shines brightly in the west-southwest and then sets in the west by around 8:00 PM CST. The best time to view it is in late twilight while it's still high. The South Equatorial Belt continues to re-form. Uranus has drifted away from Jupiter to the west and they are now separated by about 6°. They will continue to drift apart as the month progresses.

  At around 10:30 PM CST this week, Saturn rises in Virgo. By the end of the month, it will rise about an hour earlier. Last month Saturn was less than 8° from Spica, but now Saturn is moving away since it's reached a place in its orbit where it displays apparent retrograde motion. By 3:30 AM CST, Saturn culminates (passes its highest point in the night sky.) Saturn's rings are 10° from edge on, their maximum for this year.

  
On Monday morning, Feb 21, Saturn and Spica form an equilateral triangle with the Moon in the pre-dawn darkness of the southwester sky. Monday evening at 7:34 PM CST gives us another chance to catch an Iridium Flare, this time Iridium 39, in the south-southeast, also at a brilliant magnitude -8.0.

In the east all this week, an hour or so before dawn while the sky is still fully dark, Venus rises and climbs until it is lost in the glow of sunrise. Venus has lost a bit of its luster, dropping from magnitude -4.3 to -4.1 while its phase increases to more than 70% lit, but still remains the brightest object in the morning sky our "Morning Star". How can this be? Venus is drawing further away from Earth as its phase increases, so the apparent brightness is actually lower.

Unfortunately, Mercury, Mars, and Neptune are hidden behind the glare of the Sun this week.

The International Space Station (ISS) will also make several passes overhead this week that will be brighter or equal to magnitude -2.5. Saturday evening, at 6:58 PM CST, the ISS at magnitude -2.8, will pass low in the SE at an altitude of 34°. On Sunday at 7:14 PM CST, the ISS will pass mid-way up the NW sky at altitude or 49° also with a brightness of magnitude -2.8. Then on Tuesday evening, it will reach a magnitude of -2.5, again passing mid-way up the sky (42°)in the NW at 6:30 PM CST.
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