Tuesday, 2 January 2018

Lunar X and V Dates and Times for 2018

Lunar X & V Times for 2018

The Lunar X and V are optical effects which are visible on the lunar surface for about 3 hours, once a month. They are caused by sunlight illuminating the edge of craters. The X is caused by light illuminating the rims of craters Blanchinus, La Caille and Purback. The V is caused by light illuminating crater Ukert along with several smaller craters.  

The X and V are usually visible a few hours before First Quarter phase, however, due to libration, the exact time of the X and V being visible is different from month to month.  I usually publish the times of the Lunar X and V on my monthly sky notes article, but also find it useful to have this information to hand for all months of the year. As I did last year, I used the NASA Scientific Visualisation Studio Moon Phase and Libration tool, but the 2018 version. I used this to scroll through each month close to First Quarter Phase, hour by hour, until I could record the times of the X and V being visible.  The times I recorded are listed below.  These times are approximate because I just scrolled through hour by hour.  If you want to have a go a looking for a more accurate time yourself, then visit: https://svs.gsfc.nasa.gov/4604
Please note that although the X and V are visible every month, they may occur before the Moon has risen or after it has set from your location, so you will not see them every month from any one location. Please also note that the times given are in 24 clock and are in UT (the same as GMT) so you will need to correct for time zones and daylight time savings changes.

Lunar X and V Times for 2018

24th January
04:00 UT
22nd February    
17:00 UT (visible from UK)
24th March
06:00 UT
22nd April
18:00 UT (19:00 BST - visible from UK)
22nd May
06:00 UT
20th June
18:00 UT (19:00 BST - visible from UK)
20th July
05:00 UT
18th August
17:00 UT (18:00 BST - visible from UK)
17th September
05:00 UT
16th October
18:00 UT
15th November
08:00 UT
14th December
22:00 UT (visible from UK)

Happy Observing!

Mary McIntyre

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  1. The long ray that crosses the Mare Crisium and beyond is interesting me in the shot on the right

  2. The ray that crosses the Sea of Serenity is the Vessel Ray. Not sure I can see anything on Crisium

  3. Hi, As I had the opportunity to see the last Lunar-X with my kids (fascinating!!!), I wonder if there is a forcast for the year 2019.
    Another question: how did you get theses dates and time?

    1. Hi Frederic,
      So sorry for not replying sooner!
      As I explained in the text, I used the NASA dial-a-moon Moonphase and Libration tool to figure out exactly when the X and V appear. I do this by starting a day before first quarter phase then scrolling through hour by hour until I see the X appear. The 2019 dial-a-moon tool is not yet available for me to check the times, but there is a post on Cloudy Nights forum listing the times for next year. You can find that article here: https://www.cloudynights.com/topic/630098-lunar-x-start-times-2019/