John Hardcastle 1917 Lunar Theories: The motions of the Moon in her solar orbit. Timaru Herald 11 July 1917 p.3
John Hardcastle 1917 Lunar Theories: the second motion, swing in latitude. Timaru Herald 16 July 1917 p.2
"Seeing recently... in Flammarion's 'Popular Astronomy' his diagram representing the courses of the earth and moon around the sun as long-drawn-out wavy lines, crossing and recrossing each other, with his accompanying statement that the course of the moon is everywhere concave to the sun, the humorous idea occurred to me that the motions of the earth and moon resembled those of two cyclists alternately 'pacing' each other round an enormously long and narrow racing track. Such motions are entirely different from those usually ascribed to these bodies- the earth circling round the sun in an elliptical orbit, and the moon, so to speak, 'running rings round', the earth in a smaller elliptical orbit. Struck by this difference of ideas, I set about enquiring whether the motions of the moon have been treated by anyone from the heliocentric or any other extra-terrestrial point of view; looking upon earth and moon not as planet and satellite but as a pair of planets travelling round the sun in company, and changing places as leader and follower under the influence of their mutual gravitation."
The basic idea, which JH expresses eloquently, is that the gravitational attraction between the moon and the sun is more significant than the gravitational attraction between the moon and the earth. Earth and moon are not planet and satellite but are a twin planet. This might be another first for JH; this could be the first time that the earth-moon system has been considered as a double planet. The idea was nicely explored in the 1960s by Isaac Asimov in an essay in 'The Magazine of Fantasy & Science Fiction' which, despite its name published quite a lot of serious and genuine science. Asimov, assisted by Isaac Newton, compared gravitational attractions between planets and satellites in the solar system; the simple equation f = mass1 x mass2/ distance squared can be applied with interesting results. Asimov showed how the planets of the solar system dominate their satellites- with the exception of the earth-moon system, where this is not the case. JH develops this idea in two long articles in his journal of choice- the Timaru Herald (and subsequently in the Scientific American for 1919).
"Reverting to the cyclists 'pacing' motion... Luna does some pacing, and Tellus feebly responds to the invitation to 'come on', but when Luna has dropped back to the rear to give Tellus his turn, he also slows down. Tellus in fact, maintains an almost even pace in the middle of the track. Luna races up, passes on the right, gets ahead a little, then slows down, and, observing the rule of the road [in NZ] allows Tellus to pass her, and she falls back as far to the rear as she had previously been ahead.
That it is not a case of Luna 'running rings round' Tellus will be seen from the fact that the proportions of their monthly course may be likened to a cycle track, slightly curved, two miles long, and, to give plenty of room, 120 ft wide, on which two cyclists travel together. One of them, the bigger, Tellus, has a start of 60ft, and rides in the middle of the track all the way. The iother, Luna, overtakes Tellus at the half-mile, and having swung out to the right-hsand side of the track passes him. At the end of a mile Luna is 60ft ahead of Tellus, and in the middle of the track. In the second mile Luna slackens her pace, swings across to the inner side of the track, Tellus passes her at the half mile, and at the end of the two miles that represents the month's course, Luna is again 60ft behind Tellus. This is the true order of their going, month after month, as far as concerns the apparent circling of the earth and the phenomena of the phases."
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