Bakersfield Night Sky – August 6, 2011
By Nick Strobel
The Dawn spacecraft is now orbiting Vesta, the second most massive asteroid, and returning great pictures as it spirals inward towards its science orbit. Right now all of Vesta can fit inside the field of view of its camera. When Dawn gets closer in its science orbit in the middle of this month, Vesta won't all fit. Dawn's main goal is to figure out the formation process of the planets by studying up close the two most massive asteroids, Vesta and Ceres. They are thought to be remnant building block pieces of the planets. Ceres is large enough to be classified as a dwarf planet because it has enough gravity to crush itself into a sphere. Vesta is not quite big enough for that. Many of the meteorites from the asteroid belt come from Vesta because Vesta is among the closest of the main belt asteroids. The main asteroid belt resides between the orbits of Mars and Jupiter. Vesta can get close enough to the Earth for us to see it without a telescope under dark skies. In fact, it is doing that now but, as I said, it will require a truly dark sky to pick it out. Otherwise, you'll need to use binoculars.
Vesta is currently undergoing retrograde (backward) motion as we're passing by it in our faster, smaller orbit. The retrograde motion is an optical illusion that happens when we pass by an object in much the same way that a slower moving vehicle appears to move backward relative to you in your faster car as you pass by it. Vesta's retrograde loop is occuring in the constellation of Capricornus. The first star chart below gives its motion in the inset for the next several weeks. By the end of the month, you will need to use binoculars or a telescope to find it. If you go to the Kern Astronomical Society's free star party at Russo's bookstore in the Marketplace next Saturday (August 13th) from dusk to about 9:45 PM, see if you can spot the asteroid through one of their telescopes. All of Capricornus should be visible low in the southeast this evening by about 9 PM and on the night of the free star party, all of it will be visible by about 8:30 PM. A map to the star party is posted on the KAS website at www.kernastro.org.
During this week and the next, look for an isosceles triangle of bright stars in the western sky---see the second chart below. The top star is Arcturus of Bootes. It will look like a brilliant orange dot in the KAS telescope. The lower left point of the triangle is Spica of Virgo (a brilliant white dot with a touch of blue in the KAS telescope) and the lower right point is Saturn also in Virgo for the next several months at least. Saturn should still look fine in the KAS telescopes but it is now getting low enough that you'll see it really shimmer and dance about because of all the air you're looking through (that's why stars twinkle more when closer to the horizon). Tonight the Moon will be one day past first quarter phase and it will be to the left of the isosceles triangle. On the night of the free KAS star party, the Moon will be full and just to the left of Capricornus, so its glare might make it hard to see Vesta through the KAS telescopes. The night before (August 12th) is the peak of the Perseids but the nearly Full Moon will wash all but the brightest of meteors. Last year the Moon didn't ruin the view.
In the east above Capricornus, you'll find the bright stars of the Summer Triangle: Deneb on the left in Cygnus, Vega at the top middle in Lyra, and Altair on the right in Aquila. Above Vega and almost directly overhead will be the bowtie or butterfly shape of the central part of Hercules. At around midnight you will see blazingly bright Jupiter rise in the east among the dim stars of Pisces and Aries and right above the head of Cetus. If all goes according to schedule, the Juno spacecraft will now be heading toward Jupiter and arrive at Jupiter in July 2016. By the time Mars rises at 3:20 AM at the base of Gemini, Jupiter will be high up in the eastern sky. Because there are no other bright stars up in the eastern sky at about that time, if you see a very bright star in the east in the wee hours of the morning, you're looking at Jupiter—see the third chart below. By the time of the October star party at Russo's, the sky will have shifted westward enough so that Jupiter will be up in the evening sky ready to view through the telescopes.
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