Bakersfield Night Sky – September 3, 2011
By Nick Strobel
Well, the first two weeks of school have already come and gone and we're already coming up to our first holiday (Labor Day). Classes are full! Same for the William M Thomas Planetarium shows this fall. At a record breaking pace, the fall shows were sold out by the middle of the first week of the semester. In space exploration news we will have the launch of the GRAIL mission sometime this coming week (first possible launch time is September 8th). 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. This will give us insight into the history of the Moon's heating and cooling.
That insight then enables us to better understand its origin and development. A super-accurate gravity map will also be a needed navigational aid to future lunar spacecraft whether they are for science explorations or for resource extraction or for human colonization.
The two spacecraft that make up GRAIL will carry MoonKam—a camera whose image targets will be chosen by middle school students as part of the Sally Ride Science foundation in collaboration with undergraduate students at the UC San Diego. Teachers can register their classrooms at https://moonkam.ucsd.edu . How GRAIL will map the gravity field is by measuring slight changes in the distance between two spacecraft with the very original names of GRAIL A and GRAIL B (all of the naming creativity went into coming up with the GRAIL acronym). GRAIL A and GRAIL B will be in the same orbit around the Moon. As they fly over places of greater or lesser gravity, they will move slightly toward and away from each other. Instruments on board the spacecraft will very precisely measure the slight changes in their velocities relative to each other. Scientists will then translate those velocity changes into a gravity map. See the GRAIL website at http://solarsystem.nasa.gov/grail for more about the science and engineering and links to live coverage of the launch you can watch on your computer.
GRAIL's gravity-mapping technique was pioneered by the GRACE (Gravity Recovery and Climate Experiment) that has been mapping the Earth's gravity field very precisely since 2002. The climate part of its name refers to how GRACE can study changes in the Earth's gravity field due to surface and deep current in the ocean, runoff and ground water storage on land masses, and exchanges between ice sheets or glaciers and the oceans. Closer to home GRACE has been able to measure how quickly we're depleting the aquifers in the Central Valley that are, of course, crucial to our agriculture economy. GRACE confirms what local hydrologists have known about the unsustainable rate we're drawing down our water reserves. GRACE has been able to measure the groundwater depletion in places that haven't been measured before such as northern India. Now that information hasn't been too popular because such unsustainable usage of the groundwater means that our usage needs to change for our children's sake and that change is expensive.
In other space news we have a Jupiter-mass hunk of diamond orbiting a pulsar. It is probably what's left of star similar to our Sun that died to form a white dwarf and then whose outer layers were stripped away by the more massive pulsar it orbits. Pulsars are also remnants of a star but the original star is much more massive than the Sun and it dies with a supernova explosion. The core forms a neutron star that spins quickly and produces beams of energy out the magnetic poles that may sweep over us if the beams are lined up with us. An article in Time magazine said this diamond-pulsar pair are 20 trillion miles away. That may seem very far away to you but an astronomer would say that's very close. In fact that number is too close. It would be less than 4 light years away which is closer than Alpha Centauri, the nearest star to our Sun. So checking more reliable sources for astronomy news (Sky & Telescope and Science) give a distance a thousand times farther away—now that's a bit more reasonable.
Astronomers are also excited about a supernova going off in a relatively nearby galaxy, M101. This type of supernova is called a Type Ia and is the result when a white dwarf accumulates too much material from the companion star it orbits and then blows itself up. These types of supernovae are great for measuring very large distances because they have a well-known power output (i.e., we know the wattage of the light source). Comparing how bright they appear from the Earth, it is possible to derive how far away they must be to appear as dim as they are. Astronomers using Type Ia supernova to measure very large distances have discovered that the expansion of the universe is accelerating. The supernova in M101 should be bright enough to see with even a small telescope (6-inches or more in diameter). Maybe you'll be able to see it with one of the telescopes set out for you by the Kern Astronomical Society (KAS) next Saturday at Russo's Bookstore in The Marketplace. Well, with all of the light pollution in town, that might be a stretch. M101 is a gorgeous face-on spiral galaxy found above the two stars at the end of the handle of the Big Dipper in the north. There will be other interesting things to see that evening so check it out! Observing begins at dusk and goes to about 9:45 PM. See the KAS website www.kernastro.org for maps.
You may be able to catch Saturn low in the west before it sets but the sky will still be in twilight when it does set. Saturn is now in the middle of Virgo as it slowly scoots toward bright Spica on the left side of Virgo (see the second chart below). When it passes next to Spica in November you will need to look east in the pre-dawn sky. Here at the beginning of September Spica and Saturn still make a long skinny triangle with brighter Arcturus above them in the western early evening sky. Saturn will probably be too low for observing through the KAS telescopes next Saturday but the Moon will provide a nice view. Tonight it is a fat Waxing Crescent at the head of Scorpius in the southwest, tomorrow is First Quarter, and next Saturday it will be almost full in Aquarius in the southeast. The moon will be full on September 11th.
The bright planet that we'll now be able to see in the evening for this fall will be Jupiter. It is visible in the east starting at about 10:30 PM. Officially, it is in the constellation Aries but it is closer to the head of Cetus. The first star chart below shows that you can locate Jupiter by looking down and left of the Great Square of Pegasus (tilted by 45 degrees so it looks like a diamond). Jupiter will be brighter than any star in the night sky. At that time the stars of the Summer Triangle will be directly overhead at the zenith. The top of the first chart shows two of the stars of the Summer Triangle: Deneb in Cygnus and Altair in Aquila. In the middle of the month a Waning Gibbous Moon will pass by Jupiter.
Mars will be visible in the east starting at about 3 AM. It is now on the left side of Gemini. On September 15th, Mars will make a straight line with the two brightest stars of Gemini, Castor and Pollux. See the third chart below for what the pre-dawn sky will look like. That one shows that you'll also be able to see Mercury very low in the east at about 5:30 AM a bit to the right of Leo. Mercury's appearance is very brief. We'll have just a week of observing it before it gets too close to the rising Sun to spot it. On September 9th Mercury will be right next to Regulus at the bottom of the Sickle part of Leo.
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.
Director of the William M Thomas Planetarium at Bakersfield College
Author of the award-winning website www.astronomynotes.com