February 23, 2019

AstroEvent: Will Anyone Welcome the New Saros?

A Remote partial for the hardcore…(Credit: Eclipse Predictions by Fred Espenak, NASA/GSFC).

This week, we’d like to turn your attention to a unique event that no one but a few penguins may witness. July 1st kicks off the month with a partial eclipse of the Sun, the second solar in the past month and the third eclipse overall. The penumbra of the Moon will barely kiss the Earth from 07:53 to 9:22UT and greatest eclipse is a paltry 9.7% around 8:39UT. The half-moon shaped path covers a remote swatch of ocean, far from any traditional shipping lanes or air routes and only makes a brief peep above the horizon on an uninhabited shore of the Antarctic… So what, you say? Who cares about a remote, shallow, partial solar eclipse? Well, this event is notable as the very 1st start of a new solar eclipse series, saros 156. A saros period, remember, is a cycle lasting 18 years 11 days and 8 hours. The July 1st eclipse is the 1st in a span of 69 eclipses for saros number 156 spanning 1,226.05 years all the way out to 3237 A.D. Several saros cycles are in play on any given year; the last start of a solar saros was 155 on June 17th, 1928 and the next start will be 157 in June 2058… from here on out, eclipses for 156 will slowly progress northward and increase in duration before once again becoming shallow partials high in the Arctic and departing our Earthly realm.

So, will anybody see it? Well, eclipse chasers are a dedicated breed, and second only perhaps to birders or orchid hunters in the perils that they will endure to “bag the big one”…I wouldn’t be surprised if some aficionado is sitting on the distant Antarctic shore with a sat-com hookup, or negotiating to manifest aboard some wayward cargo vessel. It should be noted that one orbital sentinel, ESA’s Proba-B, will catch the eclipse from orbit… twice!

So, what does this give the rest of humanity to look at? Well, a solar eclipse means a New Moon, and thus it’s always a great chance to break another obsessive record for backyard observers; that of old/new extreme crescent moon sightings on dates leading up to and after July 1st. This month favors those placed in the South Pacific, but viewers worldwide are invited to hunt for the pre- or post- eclipse Moon!

Note: A tough to observe occultation of Venus by the Moon also occurs from 5:44AM to 8:11 UT less than 24 hours prior to the eclipse… perhaps the only observers that will have a shot at this event are along the coast of Western Africa, where the occultation occurs in pre-dawn skies. The pair will be within 12 degrees from the Sun and hence un-observable in broad daylight. A bright Venus does, however make an excellent guidepost to sight that extremely slender crescent Moon;

Venus-Moon pair at sunrise June 30th from Tampa at dawn…

…and the view from Karachi, Pakistan at local sunrise (Created by the Author using Starry Night).

The astronomy word of the week is Exeligmos. This is another wonderfully obscure term that eclipse chasers like to toss about. Think of an Exeligmos as a triple saros. Each eclipse member of the same saros is offset by about 120 degrees of longitude from the previous one because of the extra 8 hours of earthly rotation in the intervening period. Thus, an Exeligmos is a period of approximately 54 years and 34 days that brings an eclipse path very nearly back to its starting longitude from three saros intervals as before. For example, viewers across North America will get their first good total solar eclipse in many decades on August 21st, 2017, (saros 145, member 22) and one exeligmos would take you back to the North American eclipse of July 20th 1963 (saros 145, member 19)…fans of Stephen King might recognize this as the eclipse that crossed the Maine wilderness from the novel Gerald’s Game. The span of 54 plus years is just do-able in a human lifetime, and there exists an elite group of eclipse chasers that look to complete an exeligmos cycle, or the sighting of two related eclipses over a triple saros span.. myself, I caught an annular solar eclipse from the shores of Lake Erie on May 10th, 1994… that’ll make me eligible to join the exeligmos club on… June 11th, 2048! Let’s see, I’ll be…

 

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