Bakersfield College

October 5, 2013

Bakersfield Night Sky – October 5, 2013
By Nick Strobel

On Wednesday, October 9th, regardless if the government is shut down or not, the Juno spacecraft is going to fly by Earth in order to get a big gravity boost to fling it outward to Jupiter, arriving there in July 2016. At closest approach Juno will come to within 347 miles of Earth at 12:21 PM Pacific Time above the skies of South Africa. Although the span of its solar panels is pretty long, people there will still need to use binoculars or a small telescope to see it. In addition, at closest approach Juno will be in the Earth's shadow, so there won't be any sunlight glint off the solar panels. The lack of solar power while Juno is in the Earth's shadow is brief---just 20 minutes. It will emerge from the Earth's shadow over the coast of east India at a distance of about 5400 miles. Later that day in the evening our time, viewers in the United States might be able to spot it through a telescope. NASA has published the spacecraft's position and trajectory information needed by interested people to point their telescopes. You can also go to the satellite-spotting website Heavens Above to get sky charts of Juno's flyby for your specific viewing location at www.heavens-above.com/JunoFlyby.aspx .

The Atlas V 551 rocket that launched Juno in August 2011 could fling the four-ton spacecraft out against the Sun's gravity only as far as the asteroid belt. That was why the engineers planned this Earth flyby to get the extra boost needed to propel it outward to Jupiter. In a gravity-assist encounter like Juno will have with the Earth on Wednesday, a spacecraft steals a small amount of momentum from a planet. Relative to the planet, the amount of momentum lost is miniscule but relative to the spacecraft, it is a large amount because the spacecraft is so much smaller than the planet. You can find out more about the Juno flyby from the NASA webpage at www.nasa.gov/mission_pages/juno/earthflyby.html .

Why study Jupiter? Jupiter played important roles in the formation of the other planets because it formed first and it is the largest planet. Juno will be able to find out more about what the interior of Jupiter is like and how its magnetic field works by very precisely measuring the gravity and magnetic fields as it orbits Jupiter. Most of the exoplanets discovered so far are similar to Jupiter in size and mass, so better understanding Jupiter gives us a better handle on the exoplanets. Juno will also be able to finally determine the amount of Oxygen (most probably locked up in the form of water) in Jupiter which will tell us not only about the formation of Jupiter but the rest of the solar system, including Earth, as well.

There are several firsts with Juno. Juno will be the first spacecraft to go into a polar orbit (i.e., orbiting pole-to-pole instead of roughly along its equator) around a gas giant planet, it will be the first with a specially designed vault to shield the electronics since Jupiter's radiation environment is extreme, and it will the first spacecraft in the outer solar system that will use solar power. Previous spacecraft to the outer planets, including the Voyagers now leaving the the solar system and the Cassini spacecraft still orbiting Saturn, all have used nuclear power to generate the electricity they need. Juno's solar arrays are very large and also much more efficient than the ones set up on many house rooftops or over the northeast parking lot at BC. Sunlight at Jupiter is diluted by about 25X from the sunlight at Earth because of Jupiter's distance from the Sun. At Jupiter's distance, the three 28-foot solar arrays will generate about 450 Watts of power for all of Juno's needs. Knowledge gained by designing those solar arrays are going into the commercial sector to improve solar power efficiency on Earth.

At Saturn, the Cassini mission team recently announced that they had found propylene in the large moon Titan's atmosphere. When you string together propylene molecules in long chains, you get the plastic called polypropylene. Plastic containers with a number 5 in the recycle triangle symbol are made from polypropylene. No, this does not mean there are Titan creatures being careless with their food storage containers, but the detection of the simpler propylene molecule does fill in a gap in the type of hydrocarbons already known to exist in Titan's atmosphere. With worse air than Bakersfield, the atmosphere of Titan contains methane that gets broken apart by sunlight to form hydrocarbons made of chains of two, three, or more carbons. Propane is the heaviest of the three-carbon chain type hydrocarbon found in Titan's atmosphere and propyne is one of the lightest members of the three-carbon hydrocarbons found in Titan's atmosphere. The middle members of the three-carbon hydrocarbons were missing up to now. Propylene is one of those middle members. NASA is milking the plastic connection as much as possible in its news release (though the "milking" would be even more appropriate if they found the stuff for #2 plastic). The Cassini website is at http://saturn.jpl.nasa.gov .

On Mars, the Curiosity rover found that the fine-grained dust that is swept around the planet contains water molecules. Water makes up about 2 percent of the mass of the fine-grained particles in the soil. Furthermore, the water in that soil comes from water vapor in Mars's thin atmosphere. Curiosity also found one igneous rock that was more similar to terrestrial (Earth) igneous rocks than other martian rocks previously studied. Igneous rocks form by cooling molten material that came from well beneath the crust. Mars seems to have a more complex, more Earth-like geologic history than previously thought. The Curiosity rover website is at http://mars.jpl.nasa.gov/msl.

Next Saturday, October 12th, is October's free public star party at Russo's Bookstore in The MarketPlace. Members from our local astronomy club, the Kern Astronomical Society (KAS for short) will be on hand to show you the sights with their telescopes, so come by and take a peek (or more than a peek if you want) between 8 and 10 PM. They are also selling tickets for a telescope raffle to help fund the Astronomy Day activities in April 2014.

On October 18th, the Full Moon, is going to skirt the Earth's shadow to make what's called a "penumbral lunar eclipse". In a penumbral lunar eclipse, the Full Moon goes through just the region of partial shadow and not the darkest part of the Earth's shadow. Unfortunately for us here in California, the Moon will be leaving the Earth's penumbral shadow by the time the Moon gets up high enough to see above the mountains in the east. The penumbral lunar eclipse lasts from 2:50 PM to 6:49 PM our time but for us, the Full Moon won't rise on a perfectly flat eastern horizon until 6:11 PM and tack on more time if you have mountains in the east to contend with.

Something you'll have a much easier time looking for in the evening is that brilliant "evening star", the planet Venus, in the western sky. Venus continues to brighten as it catches up to the Earth in its faster, inner orbit. You will see Venus before you see any star after sunset. In fact, it is possible to see Venus before sunset if you know right where to look. A nice thin Waxing Crescent Moon will be to the right of Venus on October 7th and to left of Venus the following night (see the first chart below). By October 16th, Venus will have moved to being about a thumb-width at arm's length above the red-orange star at the heart of Scorpius, the supergiant Antares. In the early pre-dawn morning, you'll see Jupiter become visible at about 12:40 AM at the edge of Gemini. Mars rises about three hours later (see the second chart below). It is now in the constellation Leo. On the pre-dawn morning of October 14th, it will be right above the bright star, Regulus, which is at the end of the backward question mark ("the Sickle") part of Leo. Your eye will be better able to see the color difference between the orange-red Mars and the blue-white Regulus when they are right next to each other on the sky.

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