updated Lunar X calculator

Extracted the selenographic co-longitude values from the RASC Observer’s Handbook 2021 and updated my Lunar X calculator.

Phil Chow verified the events.

Looks like there are 3 good opportunities for year 2021 to view or image the letter-X pattern on the Moon, near the first quarter phase.

• Sat 20 Mar
• Tue 18 May
• Thu 11 Nov

All appear to start while the sky is still light with the peak of the event happening in twilight. Then:

• 20 Jan
• 17 Jun
• 16 Jul
• 13 Sep

are ops where the Moon is above the horizon for us near Toronto but the sky will be very bright and that may greatly hinder chances. July is borderline; maybe it will be good?

All other events occur when the Moon itself is out of sight.

§

Chris V check the Dial-a-Moon page for 2021 and reported that my March 20 prediction at ~6:38 pm EDT hits the mark!