December 9-11: The moon moves in front of Leo before sunrise December 9–11. See its close approach to Regulus and track its eastward progress during morning twilight.
by Jeffrey L. Hunt
Morning Moon Passes Leo
With the moon rising later each night, the most favorable window for observing it occurs during morning twilight. From December 9–11, look high in the south–southwest for the lunar orb as it moves in front of Leo. Watch the moon appear farther eastward each morning.
While the moon is still bright, its light washes out Leo’s dimmer stars. In this moonlight, use a binocular to trace the shape. The constellation is fairly easy to recognize as a stick figure representing a westward-facing Lion. The head, sometimes called the Sickle of Leo, resembles a backward question mark. Bluish Regulus — the 15th brightest star for mid-northern latitudes — is at the bottom of the figure. The Lion’s haunches and tail, marked by Denebola, form a triangle. Denebola is nearly 25° to the east of Regulus.
The spacing between Leo’s brightest stars equals slightly more than two outstretched fists measured from pinky to thumb.
Regulus is the closest bright star to the ecliptic, the plane of the solar system. The moon passes nearby each month, and the bright planets pass by regularly as well.
The Highlights
Here’s what to see one hour before sunrise:
- December 9: The moon, 74% illuminated, is over halfway from the southwest horizon to overhead, more than 10° to the upper right of Regulus.
- December 9 — Special event: As the calendar day ends in the Central Time Zone, the lunar orb, 66% illuminated, passes 0.5° from Regulus. For sky watchers in Greenland and Canada, the moon occults (eclipses) the star.
- December 10: The moon, 64% illuminated, is 55° above the south–southwest horizon and 2.4° to Regulus’ lower left.
- December 11: As the moon approaches the morning half-full phase (Last Quarter), it is over halfway from the south–southwest horizon to overhead, 15.5° to Regulus’ lower left and 14.4° to Denebola’s lower right.
After this passage in front of Leo, the moon moves in front of Virgo during the next four mornings. The lunar crescent has a close conjunction with Spica on the 14th.
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