Bakersfield Night Sky – November 21, 2015
By Nick Strobel
Tickets are on sale for the last two shows of the fall season at the William M Thomas Planetarium at Bakersfield College. Season of Light will be presented on Thursday nights, December 3rd and 10th. Along with a tour of the evening sky, the show includes the feature from Loch Ness Productions that traces the development of many of our winter holiday customs along with the cause of the seasons and concludes with one possible astronomical explanation for the Star of Bethlehem. Tickets are $8 for adults and $6 for children 5 to 12 years old and seniors.
As data continues to stream in from New Horizons flyby of Pluto, we continue to get surprises. The latest surprise is another aspect of Pluto's dynamic geology: cryovolcanoes---volcanoes that would have erupted water and other icy compounds! There are two broad, tall mountains at least 90 miles across and a few miles high that look very much like the broad shield volcanoes found on Earth, Mars, and Venus. At their summits are depressions over 30 miles across---calderas.
We're still trying to figure out what kept little Pluto so warm in its interior over billions of years. The only possible heat source would be the long-term decay of radioactive materials like what keeps Earth's interior warm but Pluto's store of that heat should have long ago been depleted like what happened on larger objects such as our Moon and Mars.
Pluto's atmosphere is colder and more compact than expected. Also, the rate the atmosphere is being lost is thousands of times less rapid than predicted, so Pluto is going to have the material needed for an atmosphere far into the future. As Pluto continues moving out away from the Sun in its elliptical orbit, the atmosphere may freeze out but at least the material will not be lost to space, so it can reappear when Pluto warms up again. Pluto takes 248 years to orbit the Sun and it was at perihelion (closest distance to the Sun) in September 1989.
A bit closer to home, the MAVEN spacecraft investigating Mars's atmosphere has shown how the solar wind is stripping away the atmosphere. MAVEN's orbit is very elliptical, varying from just 93 miles above the surface where it can sample Mars's upper atmosphere to as high as over 3700 miles to take UV images of the planet.
Although the rate of atmosphere loss is just 100 grams (about a quarter pound) every second, it does add up over millions of years. The loss rate can be ten to twenty times higher when the Sun lets out a large burp of plasma called a coronal mass ejection.
What prevents the Sun from stripping away our atmosphere is our strong global magnetic field that forms a protective magnetic force field bubble around the Earth. Earth has retained enough heat in its interior to keep the iron and nickel in its core molten and the rapid spin of the Earth keeps the liquid metal swirling about to make the magnetic field. Smaller Mars's interior cooled off, so its core solidified about a couple of billion years ago.
The young Sun was also more active long ago when Mars was losing its magnetic field, so the atmosphere loss rate was undoubtedly much larger than what it is today. All that's left of Mars's magnetic field is local pockets frozen in the crust.
In the early morning sky, orange-red Mars is in between the ultra-bright planets, Venus and Jupiter. The attached star chart shows that the three planets will be in the middle of an almost vertical line that connects the brightest star of Virgo, Spica, and the brightest star of Leo, Regulus. Rising up from the horizon, the order of these points will be Spica, Venus, Mars, Jupiter, and Regulus. Mars will be the dimmest of those points.
At the end of the month, Venus will pass by Spica, about half a fist width at arm's length north of (to the left of) Spica. Also at the end of the month, you might be able to spot a visitor from the Oort Cloud, the Comet Catalina. Discovered on Halloween 2013, the comet has the official designation C/2013 US10.
The comet swung around the Sun on November 15th and is now visible in the skies of the northern hemisphere, though you'll probably need binoculars to see it. The attached star chart shows its location. The Moon will wash things out a bit at the end of the month (full Moon on November 25th) but after December 3rd, the Moon won't be a problem. The closest the comet will get to Earth is a mere 67 million miles on January 12th.
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