May 28, 2016

AstroEvent: A Solstice Eclipse!


Luna entering the Earth’s shadow during the Total Eclipse of May 15th, 2003 (Photo by Author).

   One of the final astronomical events of the year for 2010 is also one of the biggest. On the night of December 20th-21st, the Moon will undergo a total lunar eclipse. This eclipse will be visible in its entirety for North American observers and at sunrise for European South American observers and sunset for observers in Australia and the Far East. First Umbral contact will begin at 06:32 UTC, and totality will last 73 minutes from 7:40 to 8:53 UTC with greatest eclipse at 8:18 UTC. This should be a fairly deep eclipse, and bets are on with how dark it will appear, as volcanic dust from this year’s Icelandic Eyjafjallajokokull volcano may play a role. And only less than 15 hours later, the winter solstice occurs at 23:38 UTC! This means not only does this eclipse occur on one of the longest nights of the year, but the eclipsed Moon is riding at its highest point along the ecliptic, a boon for northern hemisphere viewers. In fact, from Baja and southern California, the eclipsed moon should be very nearly overhead. A total lunar eclipse last coincided with the winter solstice on December 21st, 1638. Make sure to note those Danjon numbers, and make an estimate of the visual brightness of the eclipsed Moon. Our favorite method is to look backwards at the eclipsed moon through a set of binocs; the image viewed will condense down to a star-like point that can then be compared to nearby stars. Also, a minor meteor shower, the Ursids, peaks around the same morning. Rates have been enhanced in recent years, and a ZHR of 22 is predicted. Good luck, and let us know what you see!  

The astro-word for this week is Selenelion. This is the sighting of a totally eclipsed Moon when the Sun is above the horizon. How, might you ask, is this possible? Two factors come into play. Remember that the shadow of the Earth is roughly three times the diameter of the Moon. This means that the Moon can be submerged into the shadow’s edge and linger just after local sunrise. Also, the effect of atmospheric refraction means that the local circumstances of sunrise/set and moonrise/set may vary from the predicted times… alright, I’ve never seen it, either. Areas for a possible Selenelion would occur were the Moon is setting or rising during the total eclipse phase. A clear horizon and a high or preferably airborne vantage point will help in this elusive endeavor!   



  1. [...] From what I can tell, midnight to 3 a.m. will be the best viewing times here in Texas. According to Astro Guyz, the last time a solar eclipse coincided with Winter Solstice was back in [...]

  2. [...] 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. [...]

  3. [...] Ursa Minor. It generally produces a paltry 10-20 meteors per hour, but rates have been on the rise and the shower has produced very brief swarms of up to a 100 per hour historically. The source of [...]

  4. [...] lunar eclipse also presents a chance to nab what’s known as a Selenelion. This occurs when the Sun and the totally eclipsed Moon appear above the local horizon at the same [...]

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