Blue Moon (courtesy of the OMSI Kendall Planetarium)
A blue moon is usually explained as a full moon, which occurs twice in the same month. In May 2007, it is on the 2nd (3:09 am) and 31st (6:04 pm). A blue moon occurs every 3 to 4 years, when the date for one full moon falls on or near the beginning of a calendar month so that the following full moon comes before the end of the same month.
There are several different meanings for the term ‘blue moon. ‘ The phrase ‘blue moon’ has been around over 400 years, but during that time its meaning has shifted around a lot. The earliest reference was cited in The Maine Farmers’ Almanac, 1937. The almanac states that when there were two full moons in a calendar month, calendars would put the first in red, the second in blue.”
In astronomy, as stated above, a ‘blue moon’ is the second full moon to appear in a single month. However, in meteorology, the correct definition of a blue moon is the physical explanation of why, on rare occasions, the moon appears blue. The scattering of moonlight causes a “blue moon” by smoke particulate. The red end of the spectrum is scattered more than the blue end of the spectrum, which causes light seen from the moon to look more blue: hence, a blue moon.
Despite the differences in meaning, in general terms, the rarity of seeing a moon that looks blue and/or the rarity of two full moons appearing in one month prompted the well-known saying “once in a blue moon,” which means something that happens very rarely.
Asteroid Vesta at its Best
On May 31, the brightest of all asteroids, 4 Vesta, will be at its brightest. As an added bonus, it will be at opposition with a distance of 1.14 A.U. or 105,969,712 miles. During late May, 4 Vesta peaks at an unusually bright magnitude 5.4, making it easy to spot with binoculars from the city, and an easy naked-eye object from fairly dark suburban skies. (The magnitude of the stars in Ursa Major, the Big Dipper, are about 1 to 3 and M13 Hercules Star Cluster is 7) The asteroid will be brighter than any time in the past 7 years and it won’t be this bright again until 2018.
Discovered by a German astronomer Heinrich Olbers in 1807, 4 Vesta is the third largest of all asteroids after Ceres and Pallas. In Roman mythology, Vesta was the goddess of hearth, home, and family. Although only 318 miles in diameter (about the size of Oregon) its high albedo makes it the easiest asteroid to spot. In the past 10 years, the Hubble Space Telescope has shown 4 Vesta to have a geologically diverse surface. 4 Vesta orbits the Sun once every 3.63 years.
On May 31, 4 Vesta will rise at 7:55 PM at 108 degrees azimuth (SE) and will reach transit (S) at 1:04 AM at altitude of 30 degrees. A bright full moon will be just 14 degrees away from the asteriod that same evening. Throughout the month of May and June, 4 Vesta will be about 9° northeast of Jupiter. Two days before opposition, May 29th, 4 Vesta will pass only 1° from globular cluster M 107 (telescope required).
Currently there are plans to visit 4 Vesta, as well as Ceres, using the unmanned mission known as DAWN. With a checkered history of cancellations and reinstatements – the most recent being in March 2006 – the spacecraft is now expected to be launched in June 2007. Using gravity assistance, the journey is expected to fly by Mars in March 2009, then onto 4 Vesta in October 2011. DAWN will the orbit 4 Vesta until April 2012, before breaking orbit and heading off to Ceres. The encounter with Ceres will start in February 2015 and continue its exploration for several months. This DAWN mission is expected to add much to our knowledge of the inner Solar System and towards some better understanding of the formation and origin of all asteroids.
Where is 4 Vesta? : http://ssd.jpl.nasa.gov/sbdb.cgi?sstr=Vesta;orb=1
OMSI: Check out the location of 4 Vesta in Pacific NW Skies in OMSI’s Planetarium.: http://www.omsi.edu/visit/planetarium/