July 24, 2014

Astro-Event: The First Lunar Eclipse of 2012.

The partial phase of the December, 2010 total lunar eclipse. (Photo by Author).

(Note: I know, we promised a post on Xi Ursae Majoris this week; upcoming events prompted a last minute scheduling change. Trust me, it’s in the pipeline for July!)

A little over 24 hours prior to the big ticket transit of the planet Venus on June 5th-6th is another interesting astronomical event, perhaps less sexy, but worth noting.

On June 4th, the first lunar eclipse of 2012 occurs; a shallow partial centered on the Pacific basin region. There are only two lunar eclipses this year, the other being a faint penumbral eclipse on November 17th. Incidentally, four is the minimum number of eclipses that can occur in one year, two solar and two lunar, as happens in 2012. The maximum in one year is 7, but you’ll have to wait ‘til 2038 for that to happen again!

This eclipse is the direct result of the May 20th annular eclipse; two weeks on, and the Full Moon lies just close enough to its ascending node to graze the inner umbra of the Earth’s shadow. This year, the eclipse season falls around late May-early June and November; this period moves slowly through the terrestrial calendar by a period of six months minus about a week. Interestingly, this particular eclipse occurs in the constellation Ophiuchus, one of four non-zodiac constellations that the Moon can appear in along with Auriga, Sextans, and Orion. The June Full Moon is referred to as the Honey, Hot, Strawberry, or Rose Moon, perhaps eluding to the fact the that from the northern hemisphere, the Full Moon rides low in the skies and takes on a characteristic ruddy hue. This is also the most southerly Full Moon of 2012 at a declination of -21 degrees, 40′ 04″” at the moment of Full phase at 11:12UT.

Circumstances for the June 4th partial eclipse. (Credit: Fred Espenak, NASA/GSFC).

The action begins as the Moon enters the penumbra, or the ragged outer edge of the Earth’s shadow at 8:47 UTC on June 4th. After about half an hour, a slight “tinting” of the Moon’s silvery color might be noted… an easy and fun method to see this is to photograph the Moon before and during the penumbral phases; do you see the faint contrast between the two images when placed side by side?

Partial phases begin at 9:59UT. For observers in the Far East, this means that observers will see a rising partially-eclipsed Moon; for North & South America, the reverse is true and the eclipse will occur at moonset Monday morning. Mid-eclipse occurs at 11:03 UT, with the Moon 37% immersed in the Earth’s umbra. The islands of the central Pacific will witness the eclipse while it’s almost directly overhead. Hawaii, New Zealand and eastern Australia will also see the entire eclipse. The Moon departs the umbra at 12:07 UT, and leaves the penumbra at 13:20.

This eclipse is part of lunar saros 140, number 24 in a series of 77 that began on September 25th, 1597 and wraps up on January 6th, 2968. Fans of this saros series will recall the last eclipse that occurred one saros ago (18 years & 11 days) on May 25th, 1994. The next will occur on… you guessed it, June 15th, 2030. This saros has been partial since May 3rd 1958 and will not produce its first total lunar eclipse until July 30th 2102.

Occultation path of HIP 81941 during the eclipse. (Created by the author using Occult

It’s worth noting that the southern dark limb of the Moon will also occult a +7.5 magnitude star HIP 81941 for the western U.S. and Canada. Ordinarily, such as faint star wouldn’t appear on the bright lunar limb, but with the eclipse, it may be worth a try with a telescope at high magnification… HIP81941 is a solitary star in the constellation Ophiuchus.

Finally, there is a lunar connection with the upcoming transit of Venus that crosses the face of the Sun for one last time this century the day after the eclipse; namely, the Hubble Space Telescope will try to observe the transit by looking at the crater Tycho and untangling the spectrum of the Venusian atmosphere from the reflected sunlight. Refining such a technique could go a long way towards applying it to the detection of atmospheres on exoplanets.

Do get out there Monday morning for a sort of “pre-game eclipse show” to the transit of Venus on Tuesday, June 5th. If anyone is broadcasting either the lunar eclipse or the transit, let us know and we’ll give you a shout out in this space… And yes, we’ll have our big “How-to observe” post up in time for the event of the century, with facts, info, and musings that you’ll only find here!



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