Bakersfield Night Sky – September 7, 2013
By Nick Strobel
School has been in session for a couple of weeks now (three weeks for K12 schools) and it looks like another busy academic year with full classes. Last year was filled with accreditation report writing but this year's "main event" promises to be more fun---the celebrations surrounding Bakersfield College's centennial. Be on the lookout for announcements about the Centennial Ball on October 25th.
Last month's full moon prompted a question about the term "blue moon" along with some discussion in the planetarium director listserv I'm on. The Wikipedia article on "blue moon" does a good job summarizing the various usages of the term in popular culture. It's not a term used in astronomy research nor does it have any real astronomical significance so I don't address it in my astronomy classes or in the textbook I wrote for the classes. This column will be probably be the only time I get to talk about a "blue moon".
There are three meanings for "blue moon". None of them has anything to do with the actual color of the Moon. In the first meaning, the blue moon is the third full Moon of four full Moons in a season of the year where the computation for this starts with our spring equinox around March 21st. Most seasons will have just three full moons in them but because the lunar phase cycle is 29.5 days long and that time period doesn't fit nicely into our 365.25-day year, there will be occasionally a season that has four full moons. To keep the naming conventions for the first, second, and last full moon of a season the same for all of the seasons, it was decided in the 19th century (for the Maine Farmers' Almanac, no relation to the current Farmers' Almanac) to have that odd-ball third full moon of four be called a "blue moon". This was the full moon of August 20th a few weeks ago. Such blue moons happen every two or three years with next one being in May 2016.
If the first meaning seems a bit arbitrary, so is the second meaning of "blue moon" and it's the result of a mistake as well. The second meaning says that a blue moon is the second full moon in a month of the calendar we use today. Because of that 29.5-day lunar phase cycle, most months will have just one full moon in them. An article in the March 1946 Sky and Telescope contained a misinterpretation of the definition used by the Maine Farmers' Almanac which resulted in the author stating that a Blue Moon was second full moon of a month. That definition didn't catch hold in the public until a radio broadcast of StarDate in January 1980. Blue moons with this second definition can happen a bit more frequently with some years having two blue moon followed by a year or two without a blue moon. The next blue moon in the second meaning will be in July 2015.
The third meaning of blue moon is a metaphorical one meaning a very rare event as in "once in a blue moon". This is like "when pigs fly" or when a certain place freezes over. Personally, this third meaning of blue moon is what I use when I talk about a blue moon but my kids, being ever so clever, would quickly calculate when the Sky and Telescope blue moon would occur next for when they would be allowed to do some particular thing. The year 2012 was a tough year since there were two Sky + Tel blue moons in that year. At least I'll be off the hook until 2015 before I have to watch very carefully what I say around them with sentences having "blue moon" in them. Anyway, these three definitions of a blue moon are good illustrations of the question "why do they call that <xx>" (where <xx> is any strange word you want). Somebody coins a term (often arbitrarily) and if other people decide to use that word for that object or action, it becomes part of the culture (and our dictionary gets a little fatter).
Now for some real astronomy. Next Saturday is September's free monthly public star party at Russo's Books courtesy of the Kern Astronomical Society. Viewing starts at 8 PM and runs until about 10 PM or so. Saturn is now pretty hard to find in the evening twilight glow low in the west and any views through the telescope will show it shimmering and unsteady in our valley air. Venus is easy to spot---it is that very bright star you see low in the west before any other star has a hope of becoming visible. Venus continues to get closer to the Earth, so we'll see it get slightly brighter over this month. Venus passed by Spica yesterday and in another week and a half Venus will pass by Saturn on the evenings of September 17th and 18th. Saturn will be above Venus about a couple of knuckles apart at arm's length away---a nice view through binoculars. Tomorrow evening is another nice view with binoculars as a very thin Waxing Crescent Moon will be just slightly to the left of Venus---see the first star chart below. Even without binoculars that should be a pretty sight! Be sure to check that out before 8:25 PM when both of them will be too low to see in our hazy skies. On September 11th a much fatter Waxing Crescent Moon will pass above the red heart of Scorpius, the red supergiant Antares. On the night of the KAS public star party, the Moon will be a Waxing Gibbous between Sagittarius and Capricornus as shown on the first star chart below.
We will have to wait a few hours after Venus and Saturn set to see any other planets rising up. First will be bright Jupiter a little bit after 2 AM and then Mars will be visible after 4 AM. Jupiter is at the legs of the twin Pollux on the eastern side of Gemini. Mars is now at the middle of the dim constellation Cancer. In the pre-dawn morning and the following morning Mars will pass through M44, the Beehive Cluster. (Well, "through" is not the most accurate word to use since the Beehive Cluster is over 15.5 million times farther away than is Mars but this usage of the word "through" reflects the centuries-old "celestial sphere" idea with all of the objects on a giant sphere surrounding the Earth. Modern purists can say the Mars will pass "in front of" the Beehive Cluster.) Use binoculars to see them and the second star chart posted below to locate them in the eastern sky.
Another conjunction happens near the end of the month when Mars will be just below Comet C2012 S1 ISON. So far, Comet ISON hasn't been as bright as hoped (or hyped). Comet ISON will pass "very close" to Mars, just 6.5 million miles, on October 1st and several of our robotic explorers at Mars, including the Mars Reconnaissance Orbiter and Curiosity, will be looking up at the comet instead of down at Mars. Telescopes at Earth, including the Hubble Space Telescope, are also taking a close look at the comet to see what secrets it might reveal. Several astronomers at the Space Telescope Science Institute have started a blog of HST's observations of Comet ISON. Check it out at http://hubblesite.org/hubble_discoveries/comet_ison/ . You can also join in the observing campaign or just keep track of what Comet ISON is doing at the NASA Comet ISON Observing Campaign website at www.isoncampaign.org . Oh, and please, stay away from any doomsday Comet ISON websites. The doomsday cranks are recycling material from the 2012 non-event to try to scare us again and Comet ISON is now part of their menu of scary stories. Good ol' internet where the wheat and chaff mix together equally. Sigh!
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