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The Sky This Week, 2012 May 15 - 22

The Sun, twice obscured.
Sun_20120513-12h09m_01small.jpg

 The Sun, 2012 May 13, 16:09 UT, showing Active Region #1476
This large sunspot complex, one of the largest of the current sunspot cycle, covers an area
approximately as large as the area that will be covered by Venus
during the upcoming transit of 2012 June 5.


The Moon may be seen as a thin waning crescent in the pre-dawn sky early in the week. New Moon occurs on the 20th at 7:47 pm Eastern Daylight Time. At this time the Moon crosses the ecliptic directly in front of the Sun, producing an annular solar eclipse that will span the Pacific Ocean and make landfall on the U.S. West Coast. Residents of northern California, southern Oregon, central Nevada, southern Utah, northern Arizona, central New Mexico and northern Texas will see the central portion of the eclipse. This will appear as a bright ring of light surrounding the dark disc of the Moon, which will cover just under 95% of the solar disc. Persons living in the rest of the western U.S. north or south of the center line will see a partial eclipse of varying magnitude. Unfortunately for those of us on the east coast the Sun is below the horizon for the event, so we’ll miss out. This is the first central solar eclipse to cross the mainland U.S. since the annular eclipse of 1994 May 10. That eclipse belonged to the same saros (eclipse cycle) as the upcoming one. The next central eclipse we’ll see in the "lower 48" will occur on 2017 August 21; this will be a total eclipse that will span the country from Oregon to South Carolina.

The eclipse is the first of two events involving inner solar system objects crossing the Sun’s face within the next couple of weeks. While perhaps not as eye-catching as the eclipse, the Transit of Venus on June 5th will be much more interesting in the context of history. Johannes Kepler made the first prediction of a transit for December 7, 1631 but died before the event occurred. The next transit, on December 4, 1639, was observed by only two individuals, Jeremiah Horrocks and William Crabtree, from England. Transits next occurred in 1761, 1769, 1874, and 1882. Each of these events was met with a battery of scientific expeditions which hoped to use precise measurements of the positions of the Sun and Venus to measure the scale of the solar system. These expeditions met with varying degrees of success, but the ultimate goal was never realized. There were no Venus transits in the 20th Century, and by the time of the most recent one in June, 2004 the solar system’s size had been accurately measured by other means. The upcoming transit will be the last one any of us will ever see, since the next one won’t occur for 105.5 years! This transit will be visible in varying degrees to everyone in the U.S., with Alaska and Hawai’i seeint the event in its entirety. Here in Washington we’ll see the two ingress contacts of Venus with the solar limb beginning shortly after 6:00 pm EDT; sunset at 8:31 pm ends our view. The farther west you go, though, the more of the transit you’ll see. As with the eclipse, observing the transit will not require a telescope; the disc of Venus is large enough to be seen with the unaided eye. However, extreme precaution must be taken when observing the event or permanent eye damage and/or blindness will occur!

You can still observe Venus safely in the early evening sky this week. The dazzling planet is situated in the western sky and becomes easily visible right after sunset. However, as she sets her sights on the fast-approaching Sun she slips below the horizon about six minutes earlier each night. Just two weeks ago Venus set some two hours after the end of evening twilight. By the end of this week she sets when evening twilight fades! Through the telescope you’ll see her disc growing in apparent size while it becomes an increasingly slender crescent. You can now easily see this phase in a pair of binoculars.

Ruddy Mars is putting some distance between himself and his stellar companion of the past few months, the bright star Regulus in Leo. From his close approach of about five degrees a month ago the red planet is now some 10 degrees east of the star and the gap will continue to grow as he accelerates eastward along the ecliptic. His telescopic appearance is also shrinking, showing a gibbous phase just over 8 arcseconds across.

Saturn is now your best bet for long satisfying views through the small telescope. The ringed planet is just under five degrees north of the bright star Spica in Virgo, whose blue tint contrasts nicely with the warm yellow glimmer of the planet. Saturn is now well past opposition, so the shadow of the planet’s sphere now falls on the rings, rendering a seemingly three-dimensional view. Over the years I have spent many hours looking at Saturn in all kinds of telescopes, and the views have always been spectacular!

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