May 25, 2017

AstroEvent: A Loooong Central Eclipse!

Last December’s colorful lunar eclipse… (Photo by Author).

One of nature’s finest spectacles is on tap this week for observers stationed from Europe to the Far East. A total lunar eclipse of a particularly long duration is in the offing spanning the night of June 15th-16th. The duration of totality is 100 minutes, nearly the maximum 107 minutes possible. A question we frequently receive as of late is “how often does such a long eclipse occur?” Well, keep in mind that the umbra or the dark inner core of the Earth’s shadow is about 3 times the apparent diameter of the Moon as seen from Earth. For an eclipse to occur, the Moon has to be very near the ascending or descending node of the ecliptic; its orbit is canted about 5 degrees to our own and thus usually passes to either side of our 1.5 degree wide shadow. For an ideal eclipse to occur, the Moon would have to occupy that node while its smack dab in the center of the Earth’s shadow… this current eclipse will be the longest in duration until July 27th, 2018 with a duration of 103 minutes. In fact, a quick perusal of NASA’s eclipse website reveals that although this week’s eclipse is the longest this century thus far, & eclipses on 2029, 2047, and 2094 also beat it out for duration, making it the fifth longest of the century.  This could as prove to be an especially dark eclipse, as the Moon passes through the central part of the Earth’s shadow… be sure to note the Danjon number of the eclipse, as well as use our tried and true method of magnitude estimation via the reverse binocular method. Particulars of the eclipse are as follows;

Penumbral 1st contact: 17:25 UT

Umbral 1st contact: 18:23 UT

Totality Begins: 19:23 UT

Totality Ends: 21:03 UT

Umbral last contact: 22:02 UT

Penumbral last contact: 23:01 UT

The penumbral phases will only appear as a diffuse shading, while entry into the umbra will be more distinct. Also, there has been plenty of volcanic activity worldwide in hot spots such as Chile and Iceland, so the eclipse may prove to be quite colorful. And yes, this eclipse occurs in the constellation Ophiuchus, the bad boy “13th constellation” of the zodiac! (Shhh… don’t tell astrologers!) This is also the 68th eclipse of saros 118.

Photographing the eclipse with even a moderate (i.e. 200mm or larger) zoom is relatively easy; just remember that the Moon will be much darker during totality than partial phases and thus you’ll need longer exposure settings… I’ve even lost telescopic acquisition of the Moon during particularly dark eclipses!  Finally, some interesting occultations of background stars will occur during totality, the brightest of which is the +4.8 magnitude star 51 Ophiuchi as seen from the Far East… speaking of which, folks around the periphery of the eclipse (i.e. Japan, U.K. and Australia) should be vigilant for the possibility of a Selenelion, or the chance to catch totality while the Sun is still above the horizon!

Well, it looks like us folks in North America will just have to sit this one out, or at least watch it through broadcast via the Net… will tweet links (@Astroguyz) if live… We’ll just have to console ourselves with a rising pre-eclipse Honey (or do you say Strawberry or Rose) Full Moon as we eagerly await the next Total Lunar Eclipse of December 21st that occurs for North American observers at moonset/sunrise!

The Astro-word for this week is Lunation. This is simply the period of time that it takes the Moon to return to the same phase (i.e., New to New, Full to Full, etc). This is the same as our friend, the synodic month, and is on average 29 days, 12 hours, 44 minutes and 3 seconds long. This period can however, vary by up to 15 hours due to the elliptical nature of the Moon’s orbit about the Earth the period for which is getting ever so slightly longer as the Moon recedes from us by about 38mm per year. This means that eventually, total solar eclipses will no longer occur as the Moon of millions of years in the future will be visually tinier than the Sun, even at perigee. We will, however continue to enjoy total lunar eclipses during that far off epoch!

AstroEvent: Would the REAL Blue Moon Please Rise?



A Heavily Photoshoped Blue Moon...(Photo by Author).

   This week, we here at Astroguyz seek to re-ignite the controversy (or do you say non-troversy?) That swirls in some of the more obsessive astronomical circles; just what is a Blue Moon? Modern vernacular states this as simply the “second Full Moon of a calendar month,” but as researchers first point pointed out in a Sky & Telescope article in the March 1999 edition, the history behind the term is much more convoluted. [Read more...]

Astro-Challenge: Spotting the Lunar X.

The Moon a few days before 1st Quarter showing the approximate position of the Lunar X. (Credit: Photo by Author).

     This week, we bring you a unique and off-beat challenge that comes to us via reader and expert astro-calculator Ed Kotapish. Right around 1st Quarter phase, the lighting angle on the Moon gets very interesting. Craters, mountains and rills may standout in stark contrast, as the shadowed crater floors may still be submerged in darkness. Some of our favorite sights are seeing the shadows cast of long mountain ranges in the lunar highlands, or a lit peak beyond the terminator, just catching the morning Sun… what would it be like to stand there and watch the lunar sunrise for its two week long day, a half phase Earth hanging overhead?

One of the more curious and sometimes elusive features in the lunar highlands has come to be known as the Lunar X. Also sometimes referred to as the Werner X or the Purbach cross, this is visible during some lunations in the lunar highlands. The X configuration is actually the convergence of three tightly packed crater rims; Purbach, Blanchinus and La Caille. Who first sighted or coined the term Lunar X is a bit of a mystery, but descriptions of it date back to Bill Buslers’ observation of it in June 1974. Dates and times in UT for optimal sightings in 2010 are as follows:

19 Jun 07:21 to 10:23 (Far East Pacific)
18 Jul 17:29 to 20:31 (Europe)
17 Aug 03:56 to 06:58 (North America)
15 Sep 15:14 to 18:16 (Central Asia)
15 Oct 03:48 to 06:50 (North America)
13 Nov 17:42 to 20:44  (Europe)
13 Dec 08:39 to 11:41 (Pacific)

The Moon at 1st quarter generally sets around midnite local, and this week’s June 19th apparition favors the Pacific area. I would still encourage observers worldwide to check out the arrowed area the evenings of June 18th-19th… good luck, and it’ll be a first for us as well if we catch it!

The astroword for this week is Nutation. Ever wonder why the lunar landscape looks slightly different from lunation to lunation? Nutation, or the slight “nodding” of the Moon is a secondary cause of the changing face of the Moon, behind the oscillation known as libration caused by tidal locking. The largest amplitude of nutation occurs over an 18.6 year period with a motion in obliquity of 9” and a maximum in longitude of 17”. Smaller periods are known, and the cause is the tugging of the Earth and Sun. All objects can nutate, much like the secondary observed motion of a gyroscope… the motion of the Moon is a tricky and complex affair!