STOP PRESS: Jupiter and Mars are currently together in the sky in the early morning and, as is normal, any event in the sky is visited by the Moon during its orbit (not month) of 27.32122 days on average. The movement of the Moon was discussed here. I have woken up around 4 a.m. and seen the two planets, Jupiter top right and Mars bottom left for three nights. The waning crescent of the Moon was approaching from the west and could be predicted to be conjuct the two planets today so I took the following picture out of the porch door.


Photo of Moon Jupiter Nad Mars conjuction, 11th January, 2018

If the Moon was travelling on the Ecliptic (~plane of the solar system) thenit would be in line with the two planets, but it is further north than them and is on its own orbit which is angled about 5 degrees to the Ecliptic plane and in this case, the Moon is at its maximum northerly deviation from thet, in its orbit. It is the this tilt of the Moon's orbit which causes eclipses to occur only when the Moon crosses the Ecliptic at two opposite places called lunar nodes. If the Moon's orbit was not tilted, eclipses would happen twice every orbit.

Soon after this picture was taken, the Moon formed a perfect right angled triangle with itself, Jupiter and Mars on the three corners. Since the lunar nodes are on the move, it is quite unusual for a conjuction of the Moon to coincide with their conjuction at maximum deviation from the Ecliptic - leading to this triangular formation in the sky of our two closest outer planets with the Moon.

MoonJupiterMars 2

Figure 2 A rare geometry of conjunction between the Moon and Jupiter and Mars

The day was fundamental to how ancient astronomers could have had a full understanding of planetary dynamics seen from earth without our modern science. The day on earth is crucial to this capability for the way it simply relates to other time periods seen from the earth; a simplicity based upon number in which the day is a unity between numbers differing by just one unit. Such relationships are called super-particular (fractions) and the moon is the most strongly affected because it orbits the earth just as the sun also appears to, in a way that naturally generates differences of one. The Moon's daily motion provides a direct visualisation of this.


Figure 1

Judging Angular Motion