Here is a complication! The Earth's axis "wobbles."
If the line of the axis were extended to the celestial sphere, each pole would draw a slow circle, 47' in diameter, as it moved. The position of the celestial equator depends on the tilt of the axis and so the celestial equator moves bodily against the background of the stars from east to west in a direction parallel to the ecliptic. The position of the equi noxes (the intersection of the moving celestial equator with the unmoving ecliptic) travels westward to meet the Sun.
The equinox completes a circuit about the ecliptic in 25,760 years, which means that in 1 year the vernal equinox moves 360/25,760 or 0.014 degrees. The, Sun, in making its west-to-east circuit, comes to the vernal equinox which is 0.014 degrees west of its position at the last crossing. The Sun must travel that additional 0.014 degrees to make a truly complete circuit with respect to the stars. It takes 20 minutes of motion to cover that additional 0.014 degrees. Because the equinox precedes itself and is reached 20 minutes ahead of schedule each year, this motion of the Earth's axis is called "the pre cession of the equinoxes."
Because of the precession of the equinoxes, the vernal equinox moves one full constellation of the Zodiac every 2150 years. In the time of the Pyramid builders, the Sun entered Taurus at the time of the vernal equinox. In the time of the Greeks, it entered Aries. In modem times, it enters Pisces. In A.D. 4000 it will enter Aquarius.
The complete circle made by the Sun with respect to the stars takes 365 days, 6 hours, 9 minutes, 10 seconds. This is the "sidereal year." The complete circle from equinox to equinox takes 20 minutes less; 365 days, 5 hours, 48 minutes, 45 seconds. This is the "tropical year," because it also measures the time required for the Sun to move from tropic to tropic and back again.
It is the tropical year and not the sidereal year that governs our seasons, so it is the tropical year we mean when we speak of the year.
The scholars of -ancient times noted that the position of the Sun in the Zodiac had a profound effect on the Earth.
Whenever it was in Leo, for instance, the Sun shone with a lion's strength and it was invariably hot; when it was in Aquarius, the water-carrier usually tipped his um so that there was much snow. Furthermore, eclipses were clearly meant to indicate catastrophe, since catastrophe always followed eclipses. (Catastrophes also always followed lack of eclipses but no one paid attention to that.)
Naturally, scholars sought for other effects and found them in the movement of the five bright star-like objects, Mercury, Venus, Mars, Jupiter, and Saturn. These, like the Sun and Moon, moved against the starry background and all were therefore called "planctes" ("wanderers") by the Greeks. We call them "planets."
The five star-like planets circle the Sun as the Earth does and the planes of their orbits are tipped only slightly to that of the Earth. Thir% means they seem to move in the ecliptic, as the Sun and Moon do, progressing through the constellations of the Zodiac.
Their motions, unlike those of the Sun and the Moon, are quite complicated. Because of the motion of the Earth, the tracks made by the star-like planets form loops now and then. This made it possible for the Greeks to have five centuries of fun working out wrong theories to ac count for those motions.
Still, though the theories might be wrong, they sufficed to work out what the planetary positions were in the past and what they would be in the future. All one had to do was to decide what particular influence was exerted by a particular planet in a particular constellation of the Zodiac; note the positions of all the planets at the time of a person's birth; and everything was set. The decision as to the particular influences presents no problem. You make any decision you care to. The pseudo-science of astrology invents such influences without any visible difficulty. Every astrologer has his own set.
To astrologers, moreover, nothing has happened since the time of the Greeks. The period from March 20 to April 19 is still governed by the "sign of Aries," even though the Sun is in Pisces at that time nowadays, thanks to the precession of the equinoxes. For that reason it is now necessary to distinguish between the "signs of the Zodiac" and the "constellations of the Zodiac." The signs now are what the constellations were two thousand years ago.
I've never heard that this bothered any astrologer in the world.
AU this and more occurred to me some time ago when I was invited to be on a well-known television conversa tion show that was scheduled to deal with the subject of astrology. I was to represent science against the other three members of the panel, all of whom were professional astrologers.
For a moment I felt that I must accept, for surely it was my duty as a rationalist to strike a blow against folly and superstition. Then other thoughts occurred to me.
The three practitioners would undoubtedly be experts at their own particular line of gobbledygook and could easily speak a gallon of nonsense while I was struggling with a half pint of reason.
Furthermore, astrologers are adept at that line of argu ment that all pseudo-scientists consider "evidence." The line would be something like this, "People born under Leo are leaders of men, because the lion is the king of ,beasts, and the proof is that Napoleon was born under the sign of Leo."
Suppose, then, I were to say, "But one-twelfth of living human beings, amounting to 250,000,000 individuals, were born in Taurus. Have you, or has anybody, ever tried to determine whether the proportion of leaders among them is significantly greater than among non-Leos? And how would you test for leadership, objectively, anyway'.?"
Even if I managed to say all this, I would merely be stared at as a lunatic and, very likely, as, a dangerous sub versive. And the general public, which, in this year of 1968, ardently believes in astrology and supports more astrologers in affluence (I strongly suspect) than existed in all previous centuries combined, would arrange lynching parties.
So as I wavered between the desire to fight for the right, and the suspicion that the right would be massacred and sunk without a trace, I decided to turn to astrology for help. Surely, a bit of astrologic analysis would tell me what was in store for me in any such confrontation.
Since I was born on January 2, that placed me under the, sign of Capricornus-the goat.
That did it! Politel but very firmly, I refused to be on the program!
5. Roll Call
When all the world was young (and I was a teen-ager), one way to give a science fiction story a good title was to make use of the name of some heavenly body. Among my own first few science fiction stories, for instance, were such items as "Marooned off Vesta," "Christmas on Ganymede," and "The Callistan Menace." (Real swino,,inc, titles, man!)
This has gone out of fashion, alas, but the fact remains that in the 1930's, a whole generation of science fiction fans grew up with the names of the bodies of the Solar System as familiar to them as the names of the American states. Ten to one they didn't know why the names were what they were, or how they came to be applied to the bodies of the Solar System or even, in some cases, bow they were pronounced-but who cared? When a tentacled monster came from Umbriel or lo, how much more im pressive that was than if it had merely come from Pbila delphia.
But ignorance must be battled. Let us, therefore, take up the matter of the names, call the roll of the Solar System in the order (more or less) in which the names were applied, and see what sense can be made of them.
The Earth itself should come first, I suppose. Earth is an old Teutonic word, but it is one of the glories of the English language that we always turn to the classic tongues as well. The Greek word for Earth was Gaia or, in Latin spelling, Gaea. This gives us "geography" ("earth-writing"), "geology" ("earth-discourse"), "geom etry" ("earth-measure"), and so on.