November 24, 2017

Event of the Week: A New England Occultation.

Lunar occultations are always cool events; now you see a star or planet, now you don’t. The way they “wink in” and “wink out” with an improbable abruptness reminds us of the colossal velocity of the Moon about our planet. But beyond being just plain cool, they also still have scientific value; close double stars have been discovered this way, as they “wink out” in a step wise fashion. If enough observers are placed along the graze line, an accurate profile of the limb of the Moon can even be ascertained.

Brighter stars and planets pose appealing video or photographic targets.  One of the very few bright stars placed along the ecliptic for occultation is the star Antares in the constellation Scorpius. This month, the Moon is near completing an ongoing series of occultations of the bright star. We witnessed a similar occultation last summer here from Astroguyz HQ in Florida; do try to catch these last two if you can! Now for the bad news; the occultation will only be visible to a scattering of souls residing in Maine, eastern Quebec and the Maritimes. The rest of us will see a near miss. It will occur on the 11th low to the south-east at sunrise. The Moon phase will be a slender waning crescent of about 12% illumination, and sunrise will occur around 07:18 local (we used the times for our old stomping grounds of Saint Froid Lake in extreme Northern Maine; consult Heavens-Above.com, your favorite planetarium software, or drop us your lat/long for local instances). The Moon will be at about 10-20 degrees elevation, and folks in Maine and Quebec will have a chance to see first contact before sunrise, while those in the Eastern Maritimes will see it in progress after local sunrise… a good bet is to acquire Antares before sunrise, center it,  and let the telescope drive motor continue to track it (if so equipped) after the sky brightens… the last occultation of Antares this year occurs on February 7th and is centered on Anchorage, Alaska…good luck, and stay warm!

The Astro-term for this week is the Coleridge Effect. This is a curious optical effect sometimes seen during occultations and alluded to by Samuel Coleridge in his epic poem Rime of the Ancient Mariner;

While clome above the Eastern bar

The horned Moon, with one bright Star,

Almost atween the tips.

Poetic license aside, this seems to paint a picture of an impossible event; a bright star appearing in front of the crescent Moon! Perhaps part of this stems from the fact that it can be very hard to judge the edge of the dark limb of the Moon; sometimes, the vanishing act comes as a complete surprise, as the human eye is a terrible judge of cosmic perspective and distance. Do keep an eye out for this little understood and elusive event during this month’s Antares occultation, and let us know what you see!

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  1. [...] to “hang” between the horns of the Moon just prior to an occultation, known as the Coleridge Effect. This takes its name from a line in Coleridge’s Rime of the Ancient [...]

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