Sandoval Signpost


An independent monthly newspaper serving the community since 1988
  Night Sky

Turn off or shield your outside lights downward. 
Unshielded, they ruin the night sky, annoy your neighbors, and don’t help with crime.
Keep the starry skies available to everyone.

September 2016 night sky

—Charlie Christmann

Jovian Focus

Jupiter is again in the spotlight as NASA’s latest probe, named Juno, has entered orbit about the giant planet. It has taken a few years to reach Jupiter. Juno was launched in August of 2011 and finally made orbit on July 4, 2016, after an October 2013 fly-by of Earth for a quick, gravity-assisted boost in speed. NASA plans to get the craft closer to Jupiter over the next month. Currently, Juno orbits once every 53 days. NASA will fire up Juno’s engine in October to change to a 14-day orbit.

Juno is a first for NASA, which is taking several risks on this mission. First, Juno is traveling faster than any other spacecraft has. Slowing down to just the right speed for Jupiter to catch the craft in its gravity is tricky. As Juno approached the north pole of Jupiter, it fired its engine for thirty minutes in order to slow down enough. Since Jupiter is so far away, it takes more than 33 minutes for a radio signal to reach Earth, so the craft’s computers were on their own to get Juno in orbit. Yes, Juno is in orbit, so the computers worked well.

Second, Juno is not powered by a radioactive electrical generator. This ship uses solar power. But, at five-and-a-half times farther from the sun, the sunlight is only 1/25th as bright. That means Juno needs very large solar arrays to capture enough energy to operate. It also means Juno must stay in sunlight at all times; no passing behind Jupiter through its shadow.

Third, Jupiter has a very big magnetic field and it captures large amounts of the solar wind, creating deadly radiation belts. Radiation and electronics don’t mix well. Charged particles in the radiation belts can, at best, cause errors in computer memories and processing units, and at worst, fry the computer.  With Juno in an elliptical polar orbit, those radiation belts could be a hazard to the mission if Juno flies too close to the intense clouds of charged particles.

Juno’s elliptical orbit is specifically designed to avoid the worst of the radiation while allowing the craft to zoom as close as 3,100 miles above the cloud tops for a short time while spending the majority of its time relatively safe, far away from the planet.

NASA is switching on the nine experiments aboard Juno. This mission is specifically designed to study Jupiter’s atmosphere and internal structure. Two questions that might be answered are: 1) How has the Giant Red Spot survived for hundreds of years and what powers it, and 2) Does Jupiter have a solid rocky core?

Another question being asked is about the very high temperatures observed in the upper atmosphere. There is not nearly enough sunlight to account for the heating. Recent observations from Earth hint that the heating mat be associated with turbulence generated around the edges of the Red Spot as it churns counter-clockwise against the high speed wind bands on either side of it.

One feature I hope to see in the images from Juno are the Jovian Auroras. With its large magnetic field, the northern and southern lights on the planet should be interesting to see. I’m also curious to see if Jupiter has the same strange hexagonal cloud feature seen on Saturn’s South Pole.

Unfortunately for viewers, Jupiter is very close to the sun this month.

Southern Triangle

Look to the south about 9:00 p.m. The triangle of bright objects continues this month, just spread out a bit further. Mars is the eastern most planet, Saturn is the upper planet, and Antares is the lower star.

Thank you

Thanks to the Signpost for fourteen years on the Night Sky. I appreciate them allowing me the opportunity to write this article each month.

[Ed. Our pleasure, Charlie! Great column, thank you.]

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