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The Sky This Week, 2012 May 1 - 8

A "supermoon", May Day musings, and Venus prepares to take the plunge.
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Mars, 2012 April 14, 02:48 UT 

Saturn, 2012 April 14, 04:23 UT

The Moon brightens the evening sky as she waxes toward the Full phase this week. Full Moon occurs on the 5th at 11:35 pm Eastern Daylight Time. May’s Full Moon has a number of popular names, among which are the Milk Moon, Flower Moon, Corn Planting Moon, and Hare Moon. This particular Full Moon occurs one minute after lunar perigee, and since perigee coincides with a Sun/Earth/Moon syzygy it is the closest perigee for the year. Luna will be 356,955 kilometers (221,801 miles) from Earth’s center at the time. Popular media have recently dubbed such a phenomenon as a "supermoon", since Luna is about 14% larger in apparent diameter and therefore brighter than a "regular" Full Moon. Both of these measures are a bit hard to quantify unless one has specialized instruments, though, but one effect that many of us may notice are higher than average ocean tides. Luna begins the week to the southeast of ruddy Mars. On the nights of the 3rd and 4th she wends her way past Saturn and the bright star Spica. Night owls can see her rise low in the southeastern sky near the bright star Antares during the late-night hours on the 6th and 7th.

May 1st is one of the four so-called "cross-quarter" days that hearken back to traditional calendars of medieval times. These days, along with the seasonal markers of solstices and equinoxes, were the traditional days when serfs paid rent to their feudal masters. Most of these "mid-season" dates are now forgotten, but we still unwittingly observe them in various cultures. Americans are quite familiar with Halloween and Groundhog Day, but May 1st isn’t widely observed on our side of the Atlantic Ocean. However, May Day is still widely celebrated in Europe, especially in countries with a strong Celtic tradition. The fourth cross-quarter day, Lammas, falls around August 1st and is probably the least observed of these traditional times. You can think of May Day as the middle of spring or as the beginning of summer. Either way we are now in the time when the length of daylight exceeds 14 hours, which it will do until early August.

Dazzling Venus is now at her brightest for the current evening apparition, and this week you’ll find her closing in on the second-magnitude star Alnath, the tip of the northern "horn" of Taurus, the Bull. Watch her motion with respect to this star over the next couple of weeks. She will seem to inch past the star, then begin to reverse course into a headlong plunge toward the Sun. By this time in June she will be lost in the solar glare, and on June 5th she will pass directly between the Earth and Sun in a very rare transit across Old Sol’s face. How rare are such events? If you miss this one you’ll have to wait until December, 2117 to see the next one!

Jupiter may still be visible in bright twilight half an hour after sunset for skywatchers with flat western horizons, but he will be very low and probably lost in any horizon haze. He passes behind the Sun on the 13th, emerging into the morning sky by the end of the month.

Mars is now picking up speed as he pulls eastward away from the bright star Regulus in Leo, the Lion. The red planet will continue to accelerate over the next few weeks, and he will trek about two thirds of his way around the sky before he finally passes behind the Sun next April. Right now he’s still bright enough to attract attention, and his distinctive ruddy tint contrasts nicely with the blue hue of Regulus. His apparent disc size has now shrunk to below 10 arcseconds, which makes gleaning surface detail difficult for telescopes with less than eight inches of aperture.

Saturn has now taken over the mantle of the evening’s best planetary sight. Even though Mars is brighter and has a more distinctive hue, Saturn really shines when viewed through the telescope. The planet’s rings can be seen in almost anything larger than a spotting scope, and the view through a well-tuned amateur telescope can only be described as breathtaking. A four-inch instrument should reveal the famous Cassini Division in the planet’s outer ring system, and several of the planet’s icy moons should also be visible. Step up to an eight-inch telescope and the planet’s more subtle features and several more moons will become apparent. The nearly Full Moon will overwhelm your ability to track Saturn’s moons on the 6th and 7th, but by early next week you should be able to glimpse them against a darker sky background again.

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