May 2012 Sky from the Keeble Observatory Last chance in your lifetime! No, this is not a sales pitch for a furniture store or car dealership. Nor is it a tacit nod to the purported end of the Mayan calendar in December 2012 (we’ll deal with that one later in the year). Rather, it’s your last chance to see a transit of Venus. On June 5th at about 6:00 pm Ashland time the planet Venus will slip in front of the Sun. This has happened only seven times since the invention of the telescope, in 1631, 1639, 1761, 1769, 1874, 1882 and on 2004 June 8. If you look carefully at the dates, they come in pairs. Each transit in the pair is separated by about 8 years, and the pairs themselves come every 105.5 years. The transits happen in June or December, depending on where we are in the cycle. The next transits will be observable on 2117 December 11 and 2125 December 8.
Transits are a great test of orbital dynamics. While the planets all orbit in essentially the same plane (now that we’ve demoted Pluto!), the operative word is “essentially.” From Earth, the Sun is only about half a degree across. The orbital nodes have to align with the Sun within that half degree, or we get no transit. That alignment happens every 105.5 and 121.5 years, hence the pairings noted above. Edmund Halley noted that observation of the transits could be used, along with a bit of geometry and a good clock, to measure the distance to the Sun. Unfortunately, the results of these calculations are impractical due to atmospheric distortion of the telescopic images, both in our atmosphere and in the atmosphere of Venus. These make it virtually impossible to precisely determine the timing for the beginning and ending of the transit.
The Keeble Observatory at Randolph-Macon College will open for public viewing of the transit at 5:30 pm EDT on June 5th, weather permitting. We expect “first contact” about 6:04 pm, and will follow the transit until we lose the Sun behind our local horizon (which, unfortunately, included trees and buildings!). As our calculations are refined, we’ll post updates on the Keeble Information Line at 804-752-3210.
Lunar phases for May: Full Moon on the 5th, at 11:35 pm; Last Quarter on the 12th, at 5:47 pm; New Moon on the 20th at 7:47 pm; - at the New Moon there will be an annular solar eclipse, if you want to go just south of the Aleutian Islands, you’ll get a good look! - First Quarter on the 28th at 4:16 pm.
Predawn planet watchers are going to have to get up very early. Saturn is just past opposition, so it’s setting as the Sun rises. You can see Saturn all night, but Mars sets around 3:00 am. Jupiter is lost in the Sun’s glare all month.
The evening is more planet friendly – early in the month you’ll find Saturn emerging from evening twilight to the southeast. Use binoculars, the rings are special to see with your own eyes! By the end of May Saturn will be starting the evening to the south, and will set around 3:30 am. Venus will dominate the western sky at twilight for a few weeks yet, setting around 11:00 pm, but it’s moving closer to the Sun and to us as it catches up in its orbit. Note above our discussion of the coming transit on June 5th.
About three hours after sunset at midmonth, our overhead view finds the faint and probably unfamiliar constellation Canes Venatici (Hunting Dogs) near zenith. With no bright stars to distinguish this constellation, your eyes may drift to the north and start tracing down the “handle” of the Big Dipper – both familiar and incorrectly named, as the constellation is actually called Ursa Major (Big Bear). Alkaid is the star at the end of the handle, then the double binary Mizar where the handle bends. Aliothe marks the connection to the bowl. Below Aliothe we will find the front end of the bowl. Follow the line through Merak and Dubhe to Polaris, the North Star.
Twenty degrees southeast of zenith will bring your eyes to Arcturus, in Bootes. Vega, the brightest star in Lyra is east-northeast about 35 degrees above the horizon and rising. Saturn is to the south, near Spica in Virgo. Saturn is the brighter of the two. Castor and Pollux, in Gemini, are setting to the west northwest, finally clearing the skies of winter constellations. Mars is brighter than Regulus in Leo, and both are to the west southwest.
Copyright 2012George Spagna