Bakersfield College

September 17, 2011

Bakersfield Night Sky – September 17, 2011
By Nick Strobel

The GRAIL mission to the Moon launched last Saturday (Sept 10th). GRAIL stands for "Gravity Recovery And Interior Laboratory" because this mission will map the Moon's gravity field very precisely and enable us to probe the Moon's interior structure much better than before. That will enable us to better understand the Moon's origin and development. A super-accurate gravity map will also help in more precise navigating of future lunar spacecraft whether they are for science explorations or for resource extraction or for human colonization. An unmapped lumpy gravity field is responsible in part at least for Apollo 11 overshooting its original landing spot and then having to find a new landing spot on the spur of the moment and to land with just a few drops of fuel left. Unlike the Apollo mission, the GRAIL spacecraft (there are two of them) will take a much longer path to reach the Moon. They will take a much lower energy path lasting about 3 to 4 months to get to the Moon in a pole-to-pole orbit. Another about 2 months will be spent fine-tuning their orbits until they are flying in formation in the same orbit. Mapping of the gravity field will commence after that. See the GRAIL website at http://solarsystem.nasa.gov/grail for more about the science and engineering.

In other Moon exploration news, the Lunar Reconnaissance Orbiter (LRO) has returned ultra-high resolution views of the lunar surface that include the craft, instruments, and trails left behind by the Apollo 12, 14, and 17 astronauts and the moon buggy. LRO is scouting for safe and compelling landing and lunar outpost sites, locating potential resources (including water ice), and characterizing the effects of long-term exposure to radiation at the Moon. It is also providing much better maps of the Moon's topography and composition. One of the reasons LRO can do this is because it is orbiting only 31 miles above the Moon's surface. The other reason, of course, is that it has an excellent set of instruments on board. See http://lro.gsfc.nasa.gov/ for more about LRO.

On Mars, our intrepid explorer, Opportunity, has now reached Endeavour Crater. Endeavour is 14 miles wide, about 25 times wider than the previous large crater it explored called Victoria. Opportunity spent two years exploring Victoria and then took another three years travelling to Endeavour. The rocks at Endeavour's rim are significantly different than the other places Opportunity has explored so scientists are saying Opportunity has reached a second landing spot. Eventually, Opportunity will be directed to go down into the crater, but having worked 30 times longer than planned, it will take its time finding a safe entry point. Craters provide a sort of time machine because they expose layers that were covered up over long periods of time. The deeper the crater, the further back in time the rover can probe and Endeavour is a deep crater! For more about Opportunity, go to http://marsrovers.jpl.nasa.gov .

Here at home what will we see in our sky? Saturn is now gone from sight. Jupiter is the one to look for in the evening. It will be visible low in the east starting at about 9:30 PM. Technically, it is in the constellation Aries but it is closer to the head of Cetus. Jupiter will be extremely bright—brighter than any other star in the night sky. Over the next couple of months we will see Jupiter move backwards (westward) among the stars as we catch up to it in our faster orbit. The first chart below shows the eastern sky at 10:30 PM. By midnight Jupiter will be about a third of the way up in the east-southeastern sky. To the left of Jupiter will be the Waning Gibbous Moon. The Moon will be right under the beautiful Pleiades star cluster. A few nights later, on the 20th, the Moon will be at the Third Quarter phase. At 10:30 tonight the stars of the Summer Triangle will be very high in the southwest. Up top will be Deneb at the tail of Cygnus. At the bottom left corner will be Altair in the neck of Aquila and at the right middle corner will be Vega in Lyra. See the second chart below.

The third star chart below shows the view at 6 AM looking East where you can see Mars and perhaps Mercury, though Mercury may be too close to the Sun to spot without binoculars in the pre-dawn twilight glow. Mars has moved past being in line with the top two bright stars of Gemini, Castor and Pollux, and is moving toward Cancer. The bright star above Gemini to the left of the Moon in tonight's sky is Capella in Auriga. At the end of the month it will be next to the Beehive Cluster at the center of Cancer, a nice view with binoculars! The Waning Crescent Moon will pass under Mars on the evening of September 23rd and a very thin crescent Moon will pass under Regulus in Leo on the 25th of September. The third star chart below shows these events.

One last astronomical event to end this column is the autumnal equinox that officially marks the beginning of our season of fall. The autumnal equinox is September 23rd; 2:05 AM to be more precise. At the time the Sun is right on the celestial equator, the projection of the Earth's equator onto the sky. On that day, would reach the zenith point (straight overhead) for those people on the equator. On that day we'll see the Sun rise directly in the East and set due West. For the rest of the days of fall, the Sun will move further and further south until the solstice on December 21st.

Want to see more of the stars at night and save energy? Shield your lights so that the light only goes down toward the ground. See www.darksky.org for how.
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Nick Strobel
Director of the William M Thomas Planetarium at Bakersfield College
Author of the award-winning website www.astronomynotes.com

Kern Community College District