Bakersfield Night Sky – December 6, 2014
By Nick Strobel
Dinner is done, dishes washed, and as I return from taking out the trash, I look east to see the brilliant stars of Orion rising. Ah yes, December is here with the most brilliant constellations in our evening sky! December also means juicy, ripe mandarins on the tree in the backyard. Mmmm... but I digress. Orion's three belt stars, Alnitak, Alnilam, and Mintaka (from lowest to highest) make a perpendicular line with the horizon. By 8:30 PM all of the main parts of Orion are visible: brilliant blue-white Rigel and Saiph to the right of the belt stars at Orion's knees and brilliant red-orange Betelgeuse and Bellatrix to the left of the belt stars at Orion's shoulders. With a Full Moon tonight that will probably be the only part of Orion that you will be able to see. Orion's arms and shield require a bit darker sky to see.
Above Orion is the charging bull Taurus with the bright star Aldebaran at its eye. Aldebaran's color is a bit closer to the orange of my mandarins than Betelgeuse because Aldebaran is about 400 deg Celsius warmer than Betelgeuse. Both stars are in the dying stages of a star's life, the giant stage, but Betelgeuse is a more massive supergiant that will go supernova while Aldebaran is only a giant slightly more massive than the Sun and it will eject its outer layers as a planetary nebula. Betelgeuse is at least twice the size of Mars' orbit and some measures put it as large as Jupiter's orbit (it depends on what wavelength you use to view Betelgeuse). Aldebaran is a bit over half the size of Mercury's orbit.
Aldebaran is at one tip of the V-shaped pattern making up Taurus' nose and head. The rest of the stars of that V pattern are part of the Hyades cluster that is over twice as far away from us as Aldebaran. Higher above the head of Taurus are the beautiful stars of the Pleiades at Taurus' shoulders. Most people are able to see the six brightest stars of the cluster without any magnification but the stars are named after the SEVEN Pleiades sisters of Greek mythology. Perhaps one of the seven stars has grown a bit fainter since the cluster was named or the skies were much clearer than they are now. One sharp-eyed student of mine said he could see nine stars from his home outside of Tehachapi and there are reports of others being able to see up to 14 stars. Well, their eyes are a heck of a lot better than mine! A telescope will enable you to spot several hundred stars.
There has been some controversy over the distance of the Pleiades for about a decade now. A variety of techniques including recent studies using the Hubble Space Telescope had derived the cluster's distance as about 435 light years away but the ESA spacecraft Hipparcos that measured distances of nearly 120,000 stars extremely accurately had found a much closer 392 light years away. Hipparcos was a special-purpose satellite designed to measure distances extremely accurately using the parallax technique. Since the Pleiades cluster is often used as a calibration cluster for distance measurements and stellar evolution models, it is important to know its distance accurately. Hipparcos's distance measurements for the other stars meshed quite well with distance measurements from the ground.
Just a few months ago, a team used the Very Long Baseline Array to measure the distance to the Pleiades using the parallax technique. The VLBA links radio telescopes from Hawaii to the Virgin Islands to make an array with an effective resolution equivalent to a telescope with a diameter of about 5200 miles. Now, even for professional astronomers that's a BIG telescope. While the VLBA operates in the radio band it still has 50 times the resolution of the Hubble Space Telescope. A parallax measurement for something as close as the Pleiades is well within its reach and since it operates in the radio band, we don't have to worry about the atmospheric turbulence that optical telescopes have to contend with. The distance the VLBA team measured for the Pleiades is 444 light years away. Now we just need to figure out why Hipparcos distance measurement for the Pleiades is off and make sure that we don't make the same error in the analysis of the Gaia measurements of a billion stars.
The Full Moon tonight is at the tip of Taurus's lower horn, the star Zeta Tauri. The star at the tip of Taurus's upper horn is Elnath and it shares that star with pentagon-shaped Auriga. At the opposite corner of Auriga's pentagon is brilliant yellow-white Capella, a quadruple-star made of two binary systems that orbit each other. The Milky Way band is a bit sparse in the direction of Auriga because we're looking in the direction opposite the galaxy's center. The attached star chart below shows the sky at 8:30 PM when Orion and Gemini are just coming up. By 10:30 you will be able see all of Canis Major with super-bright Sirius at the nose or neck of the dog (depending on how you connect the dots) and even brighter Jupiter next to the Sickle of Leo.
Tomorrow night the Waning Gibbous Moon will be at the feet of Gemini. By next weekend, the Moon won't be rising until after midnight so you'll have a good view of the Geminid meteor shower until midnight on the nights of December 13th and 14th. The meteor shower is from the dust trail left behind by the asteroid 3200 Phaethon which is very likely a now-defunct comet that has run out of volatile materials after repeated close passages by the Sun. The dust bits from Phaethon hit our atmosphere at "just" 22 miles per second. The best viewing of the meteor shower will be from outside of town, well away from the city lights but I'll probably stay in my backyard where the sweet, juicy mandarins are.
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