★ APPLICATIONS ★ DIVERS ★ PLANETS ECLIPTIC POSITION (COMPUTING WITH THE AMSTRAD) ★ |
| Planets Ecliptic Position (Computing With The Amstrad) | Applications Divers |
MOST people know that the familiar seven days of the week are named after the planets. Thus we have (together with the French for comparison):
But why are they in this particular order? Well, it was defined by the Romans over 2000 years ago. They believed that the faster a planet appeared to move the nearer it was. This was a very sensible belief because the moon, the fastest mover, could eclipse all the others. Their order of distance was therefore as shown in Table I. Still not the right order? This is because the Romans named each day, beginning with Saturday, after the first hour of that day. That is. if you share out all twenty four hours in a day between the seven days of the week, the day the next hour - that is the first hour of a new day - lands on is the next day in our sequence. (It's a sort of MODULO 7 division.) If you count through the planets in 24s, noting where a 1 falls, you'll get the familiar sequence. Now it is a great pity that humans are slightly short sighted because it is just possible to see the next planet beyond Saturn if you know where to look. However the main reason for missing Uranus is because it travels so slowly. Nevertheless 8 planets plus 8 fingers and 2 thumbs would have ensured binary and octal counting long before computers appeared. In order to locate and identify a planet we need a reference point, and the most convenient is obtained from the most obvious, namely the Sun. This star follows the same path through the "fixed” star background almost once a year. This path is called the ecliptic and the position of the Sun at the spring equinox - on or about March 21 when day and night are of equal length - is called the First Point of Aries. It is from this point, now actually in the constellation of Aquarius (that's why we live in the "Age of Aquarius' ), that the position of ALL celestial bodies is measured. The Sun's position over the whole year is therefore quite simply how many degrees to the left of Aries 0. Consider Figure I where its path has been split into the familiar 12 zones of the Zodiac, each zone equal to 30 degrees. An important point to appreciate is that the Sun appears to rise in the east and set in the west because of the earth's rotation but also appears to move from west to east against the stars, (or Zodiac), because the earth is revolving around the Sun. This west to east movement is. on the whole, true for all the planets and can be seen in real time when the Moon eclipses the Sun, another planet or a star. By and large the planets tend also to travel along the ecliptic. Therefore we can simply define their positions as just a longitude (how far to the left of the first point of Aries).
Table II: Result from example program Calculating these longitudes is done in three stages:
Some simple trigonometry does this, but note that all we have to do for the Sun's position is to add or subtract 180 degrees to or from the Earth's longitude position since it is really the Earth that defines the path of the ecliptic and is just out of phase by 180 degrees. I have written a very simple program - 50 lines and no machine code - to perform these calculations based on the planetary data for December 31, 1974. Although simple, it is accurate to two or three degrees per century and therefore quite adequate for naked eye location and identification. No Moon, I'm afraid, as that requires quite different and more complex calculations. Enter it in Mode 2 and test it by entering the data as 6pm GMT on March 21 1972 thus: 21.75,3,1972 The result should be as in Table II. Drawing this result on to the first quarter of the Zodiac we then get the picture shown in Figure II. So if we had looked to the west at 6pm on that date we would have seen the Sun just setting exactly due west (because it was just past the equinox) with planets Mercury, Venus, Mars and Saturn strung out from the Sun along the line the Sun had just followed in the previous 4 hours (=60 degrees). As a bonus the program also tells you the day of the week, but its real use is to help identify planets and also help you to "see" how they move. For example, get their positions each week over a period of one year and plot them against the star background. You will see that the Sun moves steadily to the left with Mercury and Venus revolving around it, whereas the other planets. Another application of the program is in astrology and drawing up horoscopes. If, however, you take this subject seriously then the program is far too crude to be of any use. To differentiate between people you must have their date of birth down to a few minutes and the planet positions to within a few fractions of a second, otherwise it doesn't work. CWTA
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