Bakersfield Night Sky – August 2, 2014
By Nick Strobel
Later this week the Rosetta mission of ESA will finally rendezvous with Comet 67P/Churyumov-Gerasinmenko after more than a decade's journey. Rosetta was launched in March 2004. Along the way to Comet 67P/CG, Rosetta flew by Asteroid Steins in September 2008 and Asteroid Lutetia in July 2010. Rosetta will be the first mission to orbit a comet and land on its surface. The mission consists of two spacecraft: the Rosetta Orbiter and Philae Lander. Rosetta will start orbiting the comet this week (on August 5th or 6th) while the comet is about 3.5 AU from the Sun, between the orbits of Mars and Jupiter. For the next few months the Rosetta mission team will carefully map the comet nucleus's surface to find a suitable (safe) location on which to deploy the lander.
The Philae Lander will touch down on the surface in November. The lander has a mass of about 100 kilograms but because of the comet's very weak gravity, the weight (gravity force) the lander will feel on the comet's surface is only about the weight of a piece of paper on the Earth's surface. Therefore, the lander will use a combination of ice screws on its feet and harpoons to secure itself to the surface. Hopefully, it won't land over a spot that forms a jet of escaping gas! The minimum time for Philae's investigation on the surface is one week but it could go as long as several months depending on how the comet behaves. The Rosetta Orbiter will orbit the comet for at least one year. Comet 67P/CG gets closest to the Sun in August 2015 and the mission is scheduled to end in December 2015, so Rosetta will explore various stages of a comet's activity up close.
Since the last half of May, Rosetta has been executing a series of rocket burns to slowly change its path to Comet 67P/CG. Because real spacecraft do not have an infinite supply of propellant like the ones in science fiction shows, the space mission teams have to be very thrifty with their rocket firings and execute them while far from the object of interest so the little nudge from the rocket firing makes a significant difference further on down the road.
Each of the Rosetta spacecraft have a whole suite of instruments on board (including three from NASA) to explore this relic from the solar system's formation 4.6 billion years ago. The spacecraft is powered by a huge set of solar panels that span 32 meters, the largest of any interplanetary craft. The name "Rosetta" was chosen because we hope that this mission will the Rosetta Stone of finally understanding the language of comets. We'll better understand the connection between the local features of the interior and surface of the ice-rock nucleus and the environment of the comet's atmosphere (the "coma") and the tail. With that knowledge, we'll be able to understand what our past observations of comets from the Earth and brief flyby missions have tried to reveal to us. The Rosetta mission website is at www.esa.int/Our_Activities/Space_Science/Rosetta and mission updates are first posted on the Rosetta blog at http://blogs.esa.int/rosetta/ .
The following week will see the return of the Perseid meteor shower. Meteor showers are the result of the Earth running through the dust trail left behind in a comet's orbit from repeated passages of the comet around the Sun. The Perseids are the dust trail left behind by Comet Swift-Tuttle. The bits of comet debris hit our atmosphere at 37 miles per second and the bits tend to be a bit larger than those for other meteor showers so the Perseids can be especially bright with long trails. The peak of the shower will be on the night of August 12/13th but meteor rate will have been ramping up for a couple of weeks beforehand and it should be still be above half-maximum until the 14th or 15th.
Unfortunately, the Moon is not going to cooperate with us this year as it will be just two days past full phase on the night of August 12/13th. The moonlight will wash out the faint meteors, especially under the dusty, light-polluted skies of Bakersfield. Away from town you should still be able to spot a few bright ones. Next year the observing conditions will be much better with no Moon. I have a finder chart for radiant of the Perseids and surrounding constellations posted below .
The Moon is at Full Phase on August 10th and it will be at perigee, the closest point of its orbit around the Earth, on that same night. That makes the month's Full Moon the largest full moon of the year, so you'll undoubtedly hear about a "super Moon" in the media in the coming days. I wrote a special article about the "super Moon" way back in 2012 that is still posted on the William M Thomas Planetarium's website. The article compares the super Moon to other full moons of the year.
In tonight's sky, a fat Waxing Crescent Moon will be between the bright blue-white Spica and the orange-red Mars as shown in the first star chart below. Tomorrow night the Moon will be at First Quarter phase between Mars and yellow-white Saturn. The following night the Moon will be well to the left of Saturn. Mars continues to close in on Saturn, making noticeable changes of position between successive nights. Be sure to check out all three objects at tonight's free public star party hosted by the Kern Astronomical Society. With Sagittarius and Scorpius up in our evening sky, the KAS members will be able to show you plenty of gorgeous globular clusters and open star clusters through their telescopes as well. The great globular cluster of Hercules will be almost straight overhead. The Summer Triangle formed by Deneb in Cygnus, Vega in Lyra, and Altair in Aquila is high in the southeast at 9 PM but be sure to take a look at the nice double star in the middle of the triangle, Albireo at the beak of Cygnus through one of the KAS telescopes. The free public star party is at Panorama Park near where Linden Ave meets Panorama Drive (just west of Greenlawn Mortuary/Cemetery) from 8 to 10 PM, depending on weather.
If you stay up all night for the Perseid meteor shower, you'll be able to see Jupiter rising just before sunrise. A bit above bright Jupiter will be even brighter Venus. The third star chart below shows the August 13th sky at 5:30 AM. As Jupiter inches slowly upward away from the Sun as seen from the Earth, Venus is plunging more quickly toward the Sun. The two will be extremely close together on our sky in the pre-dawn morning of August 18th.
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