Lunar X Predictions for 2024
40°N-75°W, Eastern Time Zone 

Note: The Lunar X is not an instantaneous phenomenon; rather, it appears and evolves over several hours, so the times above are fundamentally approximate and serve only as a guide. The ardent observer should look a little early to catch the initial visible illumination. A less-dramatic Lunar X against a fully illuminated background can still be seen at least several days later. Because of the Moon’s nominal 29.5 day synodic period (phase-to-phase), favorable dates for a given location tend to occur on alternate months (unfavorable dates for 40°N-75°W are shaded gray in this table).

The 358° colongitude value for the terminator reaching the Lunar X and making it visible (see this RASC paper) and the corresponding lunar altitude/azimuth for 40°N-75°W were determined with WinJUPOS, which is freeware linked from the WinJUPOS download page.

The Cloudy Nights comparative data, derived by a different method, was presented in this Cloudy Nights post.

Daylight Saving Time for 2024 begins on March 10 and ends on November 3. The listed times are EST/EDT as appropriate for the date.

Here's a printable PDF version.

Update, February 16, 2024: The Lunar X was observed in advance of an approaching snowstorm, so it was seen through increasing cloudiness. Using an 88 mm spotting scope at 25 to 60x, the Moon was initially observed at 5:40 pm EST (sunset was at 5:37 pm) and the X was plainly visible against a dark background, although the northwest (celestial, northeast lunar) arm of the X was fragmented. It was observed again at 6:10 pm, 6:51 pm and finally at 7:15 pm (astronomical twilight ended at 7:07 pm). In each case the X was seen against a dark background, but the northwest arm was filling-in more. The final  observation, made before retiring to the WAS meeting, was definitely hampered by thicker cloudiness passing in front of the Moon. So, as suggested above, looking a bit earlier than the predicted times would be a reasonable effort.

Update, April 15, 2024: The 358° colongitude prediction for the Lunar X was 11:08 pm EDT. The Moon was observed at 8:50 pm with a 115 mm spotting scope at 35x, and no sign of the X was evident. The Moon was observed again at 11:14 pm with an 88 mm spotting scope and the X was prominent at 25 to 60x. Here's an afocal snapshot taken with an iPhone 11 through the 88 mm at 60x. Not ideal photographically, but the X, as well as the V, are clearly visible...

Update, July 14, 2024: I received a link to a NASA/Goddard Space Flight Center page with a lunar phase simulator that seems to be reasonably accurate, and certainly another interesting Lunar X checker. However, note that the times are given as UTC, but oddly, as am/pm (so 9 am = 9 hr UTC, but 3 pm = 15 hr UTC). Also, the minutes box always returns zero, regardless of what is entered.

Update, August 11, 2024: The 358° colongitude prediction of 8:15 pm EDT for August 11 was found to be a good starting point for this event. Several  observers (including myself) saw it about 8:35 pm (that's when we got to it, not when it appeared). One of them, WAS member Howard Schneck, also saw it at 8:00 pm, then captured the image below at 8:37 pm with an iPhone at the eyepiece of a small Dob (63x). The Lunar X is towards the bottom, encircled in red. In addition, the Lunar V is encircled in red too, near the middle (both along the terminator, which represents the line of sunrise here)...

Update, September 10, 2024: Although this month's Lunar X was at an unfavorable time, about half a day before the evening Moon in our area (southern New Jersey), it was clear, so I looked anyway. Using my 88 mm apo spotting scope at 25 to 60x, the X was easily seen, even though the background lunar floor was fully illuminated. At the time, WinJUPOS indicated the colongitude was 4.7° (6.7° past the 358° prediction). The Lunar V was also easily seen against a fully illuminated lunar background. The Moon was 8.0 days old and 47.7% illuminated, about 5 hours before first quarter (Sept 11 at 2:06 am EDT).

Update, October 9, 2024: The time predicted for 358° colongitude was 8:12 pm. The Moon was observed at 8:00 pm with an 88 mm spotting scope at 25 to 60x and the illuminated X clearly stood out over a near-black backgropoud.

Joe Stieber, Originally Posted December 31, 2023.