Bakersfield Night Sky – October 21, 2017
By Nick Strobel
Last week I was at a national planetarium conference in St. Louis, Missouri. One of the invited talks was about the New Horizon mission to Pluto (and beyond!) by one of the scientists involved in mapping the minerals and ices on Pluto and Charon. He shared many amazing pictures. Putting Pluto in context of its family in the Kuiper Belt, he mentioned a cool discovery (that’s “cool” in sense of “amazing” or “really interesting” and not in the sense of the cold reaches of the outer solar system) where another dwarf planet, Haumea, was found to have a ring around it.
A ring?! I thought I heard wrong because rings are for big, giant planets, not small planets or dwarf planets. I checked my AAAS Science feed and sure enough, there was the announcement about Haumea’s ring. I shouldn’t be so surprised, though. Gravity works the same on small scales as on big scales. If small asteroids can have moons orbiting them, then why couldn’t a dwarf planet have a ring around it?
Upon further research I found out that even smaller objects—a couple of Centaur asteroids that orbit between Saturn and Neptune—have been found to have rings as well. Haumea is the farthest object that has been found to have a ring … so far, anyway.
Haumea’s ring was discovered as part of a campaign to determine Haumea’s size more precisely using timing measurements of how long it took Haumea to pass in front of a background star last January. The distant star winked out a few minutes before and after the main body of Haumea blocked the star. Haumea is a squashed ellipsoid, 1443 miles across its equator but only 638 miles from pole to pole, because of its rapid spin of slightly less than 4 hours. The narrow 43-mile wide ring’s orbit is 1421 miles in radius (so it is 700 miles above Haumea’s equator). The ring particles orbit once for every three spins of Haumea, a 3:1 spin-orbit resonance.
Although the observations were done at the beginning of the year, the announcement had to wait until October for the analysis and peer-review error-checking process of science to work through. The peer-review process of science is how we take into account the fallibility of humans and to make sure we don’t fool ourselves.
Previous observations of Haumea turned up the presence of a couple of moons orbiting Haumea. Those observations of the moons enabled us to get a mass for Haumea. The new measurements of Haumea’s size enables us to get a more accurate figure for its density, just 1.9 times the density of water. That’s the same density as Pluto and Haumea is probably a 50-50 split of rock and water ice and it’s darker than we originally thought, reflecting just half of the feeble sunlight that hits it.
In galaxy news, the case for our home galaxy, the Milky Way, having four spiral arms instead of just two like our neighbor Andromeda Galaxy, became much stronger with the direct measurement of the distance of a star formation region on the other side of the Milky Way. Using the Very Long Baseline Array (VLBA), astronomers were able to measure the parallax of the star formation region. The VLBA is an array of ten radio telescopes spread across the earth from Hawaii to the Virgin Islands. They are connected together to produce the resolution of a single telescope of the same diameter—a planet-size telescope! With a resolution in the microwave and radio band 50 times better than what the Hubble Space Telescope can do in the optical, the VLBA is the only device we have that can measure the tiny parallax angles of objects on the far side of the Milky Way. The parallax gives us the distance using basic trigonometry.
The star formation region is 66,500 light years away and are part of the recently-discovered Outer Scutum-Centarus arm of the Milky Way. Other observations of objects have given positions that implied the existence of the outer arm but their distances were derived using assumptions of how velocities depend on distance from the galaxy center. The parallax distance method is a direct measurement with no assumptions (as good as you can get besides using a tape measure).
Tonight and tomorrow night are the peak of the Orionid meteor shower. The radiant of the meteor shower (the point from where the meteors appear to streak away) is next to the club in Orion’s right hand (in the area between Orion and Gemini’s feet in the attached star chart). Therefore, the Orionids won’t pick up until the pre-dawn hours of the night.
Early morning risers will be able to see orange-red Mars rise up shortly after 5 a.m. followed by Venus rising an hour later. Both planets are in the constellation of Virgo.
Next Saturday, October 28, is the last of the free public star parties for 2017 hosted by the Kern Astronomical Society. KAS will hold this public star party at Barnes & Noble near Hwy 99 and California. No observations of meteors, Haumea, or star formation regions on the other side of the Milky Way but they’ll have the moon, beautiful star clusters, and glowing nebulae to see through their telescopes.
Director of the William M Thomas Planetarium at Bakersfield College
Author of the award-winning website www.astronomynotes.com