May 30, 2020

AstroEvent: A Lunar Occultation.

Lunar occultations can be fun events to observe. As the moon continues its 27+ day long path around our planet, it sweeps out a 0.5 degree wide path and occasionally covers up a distant background star or planet. Such occasions can be fun events to observe, as the star winks out and later seems to pop back into existence from behind the lunar limb. Such an event occurs this Sunday, the night of March the 13-14th, as the waxing crescent Moon occults the semi-bright star Mu (µ) Geminorum.

Mu Gem sits at magnitude +2.9 and is an easy naked eye star. The moon will be about 61% illumination, and the best sighting ops will be during ingress behind the dark limb of the moon. During egress, Mu Gem will be tougher to spot. US East Coasters will have the best view of the event, as those roughly west of the Mississippi River will have daylight to contend with. The link above from the International Occultation Timing Association provides the circumstances for your given location. Mu Geminorum is undergoing a series of lunar occultations this year, and this Sunday’s is one of the best!

The Astro-term for this week is Graze Line. If you are lucky enough to be along the edge of the path above, you might just catch a grazing occultation, as the star appears to wink in and out behind the lunar limb. This is because the star is actually shining between and through the mountain peaks and valleys as seen from your line of sight. Such a view is an eerily three dimensional experience in what seems like a two dimensional sky. But beyond just pure aesthetics, an accurately timed video from the graze line can produce a profile of the lunar limb, as well as potentially tease out any close stellar companions of the distant star.

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