Lunar conjunctions with Saturn (tonight 26th-27th) and Jupiter (27th-28th June)

For general interest, please note if you have clear intervals tonight and tomorrow night, you'll be able to view conjunctions of the Moon with Saturn (happening tonight 26-27 June) and Jupiter (occurring the next night 27-28 June).

The Moon was recently full and will appear almost full in these conjunctions, passing below the bright planets as it heads towards its southern latitude extreme (Saturn and Jupiter are also below the same ecliptic plane but not as far as the Moon which heads for a 5 deg separation from the ecliptic just after the Jupiter conjunction -- Jupiter is closer to 2 deg below the ecliptic now).

We pass Saturn on 2 Aug and Jupiter on 20 Aug (these events are called oppositions), after their heliocentric and geocentric conjunctions last October and December respectively. Since Jupiter is moving 2.5 times as fast as Saturn, this means that as of today, Saturn is around the position of a 31 July opposition and Jupiter is around the position of a 15 Aug opposition.

There will be a similar pair of conjunctions of the Moon with these planets with the July full moon (night of 23rd-24th) and the August full moon (night of 22nd-23rd). The details will change from event to event. On the night of the 24th-25th July the moon will appear roughly midway between the two planets (as seen from Ireland).

In this present case, the Moon and Saturn will rise just around midnight, Saturn may appear first over the horizon as it is somewhat closer than the Moon to the ecliptic plane.

The Moon's 5 deg orbital inclination (to the ecliptic plane, not the earth's equator) undergoes a rapid 18.6 year precession (retrograde or towards the west) which means that at intervals of 18.6 years, the winter and summer full moons can appear at extreme points five degrees above (winter) and below (summer) the ecliptic. This has the effect of placing the full moon very low in the south at transit at those times. The next such declination extreme is in 2024 so the Moon has already started to get into the high 24 to low 25 deg declination range at these times (the extreme is nearly 29 deg). As a result the full Moon in June and July appears a bit lower in the south than the midwinter and January sun positions. You'll notice how low the moon is riding, especially if you live in northern regions where it stays even closer to the horizon. There would be places in Iceland or Scandinavia where these summer full moons would only make very brief appearances over the southern horizon.

So tonight you will be able to see the Moon close to Saturn, and tomorrow night it will be close to Jupiter. Here's a rough calculation of how long it would take the Moon to appear to pass from near Saturn to near Jupiter. They are currently about 15 days apart in terms of opposition (will be 18 by August). Since the Moon takes 27.5 days to travel around its orbit and return to a conjunction with these slow-moving planets, and 15 days is 1/24 of a year, then it would take 1/24 of the 27.5 days which is about 1.1 days. A minor adjustment would be for lunar perigee or apogee since the Moon is moving faster at perigee; at this time, the Moon is closer to perigee than apogee and moving a little faster so would adjust the estimate to one day. This will lengthen out for two reasons, first the growing separation of the two planets, and secondly the slower speed of the Moon in its orbit (perigee currently occurs a few days before this portion of the orbit).

Another thing you can watch for over the next 2-3 years is that the Moon will get closer and closer to Antares, the bright red star that is visible in the south around midnight. Eventually near and just after the declination maximum, the Moon will have a series of occultations of Antares. There was a series of occultations of Jupiter and Saturn earlier this year, and there will be another one in a few years when the southern latitude max in the Moon's orbit moves away (towards the west) from their position, and since they are also moving to lower celestial latitudes, this process will be fairly rapid and the occultations will not last for very many orbital cycles.