Bakersfield Night Sky - November 18, 2018
by Nick Strobel
Tickets are on sale for the holiday tradition favorite “Season of Light” that will show at the William M Thomas Planetarium on November 29 and December 6. After that the planetarium will be closed during Bakersfield College’s winter break.
Three days before the first Season of Light show, on November 26 at about noon Pacific Time, the Mars InSight lander should touch down in the southwestern part of Elysium Planitia, a very boring flat plain near the equator. NASA picked this spot, not for the view but for the perfect place to deploy the instruments that would probe Mars’s interior.
The place needs to have rock that can be penetrated by the 16-foot long heat-flow probe. The heat probe will tell us how heat flows inside Mars and whether or not Mars really is formed of the same material as Earth and its moon. The place also needs to have calm weather all (or most of) the time so the seismometer is not buffeted about by winds. The seismometer will measure vibrations from any marsquakes that might still be happening as well as from meteorite impacts. In a way analogous to how we use ultrasound to probe the interior of our bodies, geologists use seismic waves to figure out the planet’s interior composition and structure.
Despite what you saw in the movie “The Martian”, the winds are not as strong as the winds on Earth because Mars’s atmosphere is over a hundred times thinner but InSight’s seismometer is very sensitive to vibrations—it can detect vibrations smaller than the width of a hydrogen atom. The seismometer will be inside a protective dome that will protect it from the wind as well as from the temperature swings of about 110 deg F between day and night.
InSight’s landing site will be close to the equator, so the solar panels will receive the sunlight needed to operate year-round. The site is also low enough in elevation that there will be enough air above to help InSight land safely using a combination of parachute and retro-rockets. Finally, the site does not have a lot of large rocks that would tip InSight. Flat boring land with boring weather: just the thing for a mission focused on the interior of Mars.
A radio science experiment will measure the wobble of Mars’ spin by very precise tracking of InSight’s location on Mars. How much Mars’ interior sloshes about will tell us about its composition and how much is still molten. All three instruments working together will give us the best insight into Mars’ interior. By the way, “InSight” stands for “Interior Exploration using Seismic Investigations, Geodesy and Heat Transport” and it’s not a typo to have the uppercase “S”. Go to https://mars.nasa.gov/insight/timeline/landing/watch-online/ to watch the landing online and the InSight homepage at https://mars.nasa.gov/insight/ to learn more about the InSight mission.
A little closer to home the periodic comet 46P/Wirtanen will make a particularly close flyby of Earth in mid-December at just 7.1 million miles. Right now the comet is among the dim stars of Fornax below Cetus and Taurus (see the star chart below). You’ll need binoculars to see it but there’s a reasonable hope that it’ll get bright enough to see it with the naked eye under a dark sky (not Bakersfield) by early December. By then it will be among the stars of Eridanus, heading toward Taurus.
I use tentative language (“reasonable hope”) to describe how the comet will brighten because comets are notorious for not behaving as we predict they will. A lot depends on where the volatile material is with respect to the surface rock + dust material and how strong the rock + dust holds itself together—things we can’t see from our vantage point on Earth. Comet 46P/Wirtanen has a history of being especially active and this flyby of Earth will be especially close, so “reasonable hope” seems appropriate. The small comet (nucleus is just a third of mile across) orbits the sun every 5.4 years. The next close approach to Earth will be in October 2029 at a distance of about 71 million miles (or ten times farther than this year’s close approach). See Gary Kronk’s Cometography webpage about this comet at http://cometography.com/pcomets/046p.html for a history of discovery and observations of this comet.
In tonight’s sky a bright gibbous moon will provide a lot of light to wash out much of what remains from the Leonid meteor shower that peaked last night. The moon will be at full phase for Thanksgiving. Jupiter is now lost in the glare of the sun as it heads toward conjunction with the sun on November 26 when it will be behind the sun. Mercury is barely visible low in the southwest just after sunset as it races towards it conjunction with the sun on November 27 when it will pass between us and the sun. Saturn is just above the teapot part of Sagittarius low in the southwest when twilight ends around 6 p.m. Mars will be the only planet up after 7:30 p.m. It will be in the southern part of Aquarius.