Our Mysterious Moon
How did our Moon get to be up there? Astronomers are now on their fourth theory about this, and I don't reckon they should be allowed any more! Each theory is a bit less credible than the one before. First, they had an early Earth splitting in two, with Luna emerging from the Pacific Ocean. That lasted quite a while, but eventually it was deemed that there wasn't enough angular momentum in the system for it to have happened. Instead, Luna had to be captured, drifting in from outer space. That seemed OK, until the Apollo visits to the Moon in the 1960s; they then realised how very difficult it was to get into an orbit where capture took place, or to imagine a nearly-circular orbit resulting from capture; but also because a few key similarities were found, between earthly matter and Moon rock. So, instead, the 'accretion' theory developed whereby debris orbiting the Earth somehow congealed into Luna. But, debris impacting together would tend to slow down, and so drift nearer to Earth, whereas Luna is rather far away and gradually receding from us. So finally they have developed a big-impact model, BLAM! with some passing asteroid or whatever, and Luna somehow emerges. Pull the other one.
The problem with these creation theories, is that our Moon has some rather beautiful symmetries in its orbit and in the patterns it weaves between Earth and sun. To start with, it is at just the right distance to achieve the beautiful and frightening eclipse of the Sun. Sol is four hundred times larger than Luna, but also four hundred times further away, so that, by a convenient scaling, they both appear as the same size. Sometimes, during a total eclipse, the fit is exact enough to make 'Bailey's beads,' seen as the solar corona glitters through the valleys of the mountains of the Moon.
Luna is far enough away from Earth not to be held within its gravity field, and this is paradoxical: other planets hold their satellites closer, bound firmly within the hold of their gravity pull, whereas Luna is always more strongly pulled by the Sun than by Earth. For this reason astronomers properly call it a 'companion planet' rather than a satellite. Also, Luna orbits in a plane all of its own, differing from any other in the solar system, tilted at five degrees to the ecliptic. If Luna properly 'belonged' to the Earth, i.e. had spun off from it, one would expect it to orbit in Earth's equatorial plane.
Nine are the moons between conception and birth, a uniquely human feature: 266 days or maybe slightly less is the average duration of human conception, and 29.53 x 9 = 266 days. Although the menstrual cycle is often quoted as 28 days on average, the evidence doesn't confirm this; large, careful surveys have generally found it to be between 29 and 30 days (1) on average. Between twenty and thirty years of a woman's age, i.e. the peak child-bearing years, that mean value was found to be 29.5 days, while 28 days was the mean length for women in their thirties, and 27 days for women in their forties. It was 30 days or longer for teenage girls below 20 years of age. Thus, during the main childbearing years, the female period's duration is closely synchronised with the lunar month.
Now and then, glows light up on the lunar surface. They may spread across a crater floor: red or purple, or sometimes brilliant white for a moment, and teams of astronomers patiently log them as they shimmer across its surface. (2) One is short of an explanation for these, as Luna is supposed to have been volcanically dead for aeons. The glows often occur, as Patrick Moore helpfully observed, on the shores of lava seas.
Synchrony of the Saros:
Above: Eclipse tracks over one Saros cycle of 18 years. The 12 eclipses whose paths of totality are shown belong to one family, determined by the law of Saros. The displacement in latitude and longitude can be clearly seen.
Earth and Her Moon
John Michell's Famous Construction
Earth has a mean diameter of 7,920 miles, the Moon 2,160 miles (radius 1,080 miles). Start by drawing a horizontal line length 4. With compasses and ruler divide the line in half and then half the halves; now a vertical length of 3 can be swung up and so a 3-4-5 triangle made. From here progress as shown in the top part of the diagram. Circles representing the Earth and the Moon can now be drawn with over 99.9% accuracy. The circle represents Heaven, the square represents Earth. With π as 22/7 a heavenly circle passing through the centre of the Moon has a circumference of 44 - the same length as the perimeter of the earthly square around Earth. Thus the Earth squares the circle of Moon.