Lunar X & V
August 2025 :
One of my favorite “features” on the Moon is the Lunar X & V. This phenomenon is predictable and occurs on a monthly basis. (See table 1).
The Lunar X (also known as the Werner X) is a clair-obscur effect in which light and shadow creates the appearance of a letter 'X' on the rim of the craters Blanchinus, La Caille and Purbach. The X is visible beside the terminator about one-third of the way up from the southern pole of the Moon. The Lunar V forms along the northern part of the terminator near the crater Ukert. (See image)
I advise all amateur astronomers to consult this table to see if the Lunar X & V will be visible from your location. Time and date are listed in Universal Time therefore each individual observer will need to convert to their local time in order to observe the event. The easiest way to do this is with a free program called WinJupos. (https://jupos.org/gh/download.htm) WinJupos states both Universal Time and Local Time for the Sun, Moon and Planets. Enter your latitude and longitude first, then enter Universal Time stated on the table and your local time will appear above (See figure 1). For many observers in the Western Hemisphere, local time will be the day before. For example, the Lunar X & V occurred according to the table on July 3, 2025 at 00 hours 15 minutes UT which for the New York Time Zone is the day before July 2, 2025 at 20:15 or 8:15PM local time. If you went out on July 3rd, the X & V would have occurred already and would not be visible. Therefore, it is imperative that Universal Time be converted to Local Time in order to witness the event.
Fortunately, the X & V will appear and last several hours later than the stated time on the table. This is a good thing, since it may be cloudy at the start of the event and an hour later the clouds may have dissipated. The Lunar X & V will still be visible! Another interesting phenomenon I previously witnessed was that the V was visible at the time stated on the table, but the X was not fully formed. It took several hours for the X to appear as a full X. This makes the observation even more interesting since you can watch the X appear in real time!
In conclusion, the Lunar X & X is a monthly phenomenon not to be missed. Check the table, convert Universal Time to Local Time and see if it will be visible from your location. If it is, then get out your telescopes and cameras and submit your observations to ALPO’s the Lunar Observer care of David Teske. david.teske@alpo-astronomy.org
