The Moon has two orbital rhythms that vary by about two days: The sidereal rhythm (27.3 days) is the time takes the Moon to complete one orbit around Earth; and the synodic rhythm (29.5 days), which is the time it takes for the Moon to catch up with the Sun again. These two rhythms are different because the Earth is moving.
And here’s what’s really fascinating:
Sunspots occur at a certain latitude on the Sun’s surface, and at this latitude, the Sun has a rotational period (27.6 days) nearly equal to the Moon’s sidereal rhythm. The planet Saturn has an orbital period of 29.5 years, which is the same number of days in the Moon’s synodic rhythm. This is an incredible cosmic harmony, and we’re living right within it, because on the Earth, we live within or below the Moon’s orbit, so everything that comes and goes in our cosmic environment has to lock in with our Moon in order to be realized here.
That’s where this week’s Thunder Moon comes in. It will be Full on Friday, July 23rd, at nearly the exact same place where Jupiter and Saturn had their Great Conjunction at Winter Solstice last year. So it’s as though the moonbeams will resound with the meaning of what that great meeting was all about. Imagine the Moon is like our cosmic doorkeeper, and now the doors are flung open, and we’re invited into the room where it happened. And take John Keats with you, from his Endymion:
Nor do we merely feel these essences
For one short hour; no, even as the trees
That whisper round a temple become soon
Dear as the temple’s self, so does the moon,
The passion poesy, glories infinite,
Haunt us till they become a cheering light
Unto our souls, and bound to us so fast,
That, whether there be shine, or gloom o’ercast;
They always must be with us, or we die.
Thundering, thundering, all around the square!
Up above, Sky&Telescope‘s image of the Thunder Moon, now a waning gibbous, having graced the Great Conjunction point, moves along to confer first with Saturn, then Jupiter, as it races toward the dawn.