October 22, 2017

Astro-Event: A Fine Total Lunar Eclipse.

Our photo of last December’s total eclipse.

Mark your calendars; this Saturday, December 10th a total lunar eclipse graces our fair planet, and a good swath of humanity will get to see it. This particular eclipse occurs at sunset/moonrise for observers in central Europe, the UK, and north-eastern Africa westward, and just before sunrise/moonset for all of North America except the U.S. eastern seaboard and the Maritimes. The Far East and Australia will see this eclipse in its entirety, and yes, Astroguyz HQ in Florida will (gasp!) miss out. But don’t worry; we’ll give it the ‘ole college try to at least document the penumbral start of the eclipse. Compare photos of a penumbral eclipse and a normal Full Moon & you CAN see a difference! We’ll also be tweeting out the plethora of links of folks live webcasting this eclipse that are bound to crop up via @Astroguyz… Thus far, one potential live link has presented itself via the Skywatchers Association of North Bengal, India. Anyone else? Anyone? Bueller?

Totality for this eclipse is 51 minutes and 8 seconds long, and the total length including partial phases is 3 hours 32 minutes and 17 seconds. Incidentally, this is the shortest length for totality until April 4th 2015, but still respectable. This is also the last total lunar eclipse until April 15th 2014; 2012 only features 2x lunar eclipses (a partial and a penumbral) and 2013 has three, (2 penumbrals and a partial!)

The path of the Moon this Saturday through the Earth’s shadow. (Credit: NASA/GFSC/Fred Espenak).

Partial phase begins at 12:46UT, and totality runs from 14:06 to 14:57UT. Final partial phase ends at 16:18UT. This eclipse is part of saros series 135, member 23 of 71. Incidentally, we remember watching the last lunar eclipse from this series in 1993 from Florida!

This would be a great time to try your hand at eclipse photography; if you can shoot the Moon, you can get decent photos of an eclipse. Practice the evening before when the Moon is nearly Full if you’ve never tried your hand at astrophotography. At about ½ a degree of arc in size, the Moon is a deceptively small target. A zoom of 200mm or greater will yield a fairly large image; we prefer a 400mm with a 2x tele-converter shooting in manual mode. Speaking of which, be ready to lengthen those exposures as the Moon enters totality by as much as 10 seconds or so to get decent pics of the darkened Moon. As exposure settings go past 3 seconds or so, you’re going to want to have the camera piggy-backed on a tracking mount so that the exposures don’t blur, especially if you’re really zoomed in. That being said, folks are taking great shots of the Moon simply by coupling up their smart phones to their telescope!

Live in the light to shaded regions? You just might see the eclipse! (Credit: NASA/GSFC/Fred Espenak).

It’s always fun to try and estimate the brightness and color of the Moon during mid-eclipse. Some eclipses may be a bright copper-to-orange in color, while an exceptionally dark eclipse can cause the Moon to practically vanish all together! We suspect that this eclipse will be exceptionally bright along the limb, as the body of the Moon doesn’t quite pass thru the core of the Earth’s umbra. The scale of measuring the color and degree of the eclipse is known as the Danjon number and estimations can give a fairly accurate measure of the levels of aerosols and dust suspended in the Earth’s atmosphere that the sunlight is filtering through. Sky & Telescope often seeks crater contact timings as a way of refining the size of the umbra at the distance of the Moon. Also, the International Occultation Timing Association has published a list of bright stars that the eclipsed Moon will occult as it drifts through the constellation Taurus. Interestingly, we note that the 6th magnitude variable star and close (separation = 0.3″) double 105 Tauri lies along path of the Moon. We’ll get updates on those timings out as they appear on… you guessed it; our Twitter-feed.

In the realm of the strange and curious, I’ve also done estimates of eclipse brightness via looking through binoculars… the wrong way! This reduces the Moon down to a star-like point that you can then compare to other stars of known magnitude. The trick to this method is knowing how much of that extinction in brightness is due to the particular set of binocs you’re using. Observe bright Venus (mag -3.8) or Jupiter (mag -2.7) via this method to gain an accurate correction number; both are currently well placed in the evening sky. Another interesting challenge that I’ve never seen done is catching the ISS transit an eclipsed Moon, which should be possible as there are several opportunities worldwide during partial and total phases. But keep in mind; the ISS will most likely be in the Earth’s shadow as well! Also, NASA’s Lunar Reconnaissance Orbiter should have a good view of a solar eclipse in progress as the Earth passes in front of the Sun from its 50 km orbit vantage point.

Also, it’s interesting to note that the Geminid meteors peak on December 14th, only 4 days after the eclipse; It’s not out of the question that US West Coast viewers just might see enhanced rates of meteors in the AM skies while the Moon is eclipsed. An interesting project would be to video the eclipsed Moon with a high speed camera… you just might nab a Geminid impact on the Moon!

Finally, a unique possibility presents itself for those positioned between the U2 and U3 bands (see above)… to catch an eclipse phenomenon known as a Selenelion. This occurs when the eclipsed Moon and the Sun are both  above the horizon simultaneously. Strange, but it can happen, as the shadow of the Earth is almost 3x larger than the apparent diameter of the Moon. Lunar apogee also occurs 4 days prior on December 6th, resulting in a slightly smaller a slower moving eclipsed Moon. Earth is also approaching perihelion next month, allowing for a slightly larger shadow. The “path of Selenelion” crosses North America from Arizona to Hudson Bay (sunrise) and crosses the Middle East through central Europe and Norway at local sunset. Observing from an elevated sight will also boost your chances of crossing this rare phenomenon off of your life list… good luck!


  1. [...] marks the first total lunar eclipse visible from since December 10th 2011, which was visible at moonset from North America, and marks the start of the first of two eclipse [...]

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