Hi! an astronomy question.

Hello!!

So a couple of weeks ago I joined an astronomy activity in a tech museum. As a part of the activity, we were explained a bit about constellations, and were shown several softwares that simulated the sky activity in any given year. The people there told us why only 12 of the 88 constellations above are used as zodiac signs, and why astrology itself wasn't accurate: It seems that astrologers overlooked a certain part of the earth's movement, and it isn't as exact as one would believe. I can't explaint it better since english isn't my native tongue.... but they had a few examples: for instance, a man said he was born on late october, and therefore he should be scorpio, but the program simulated the sky on the day he was born, and the sun wasn't even near that constellation, it was too far and in the middle of some other sign. I downloaded one of the free softwares they talked about, and did some more experiments with other dates, and only like two out of 20 were sort of related to the sun sign they were supposed to be.

So my question is... I don't know. I read somewhere that astrology only used the names of the constellations but had nothing to do with actual astronomy, but then how do you people build your charts??? I know for a fact that the software isn't broken or anything, and the guys at the museum are astronomers and scientists..... What do you think about that???

Well your teachers may know something of Astronomy but they are startlingly ignorant of Astrology.

Western Astrology uses the Tropical zodiac - that is the signs are measured from the March equinox. This measurement dates back to the time of Ptolemy, who also knew a thing or two about Astronomy.

Your teachers are referring to the sidereal zodiac (assuming that they know the difference). That measures the zodiac from a point in the constellation of Aries. The exact point is not agreed, and you will find a number of versions.

Now in India (and elsewhere where Indian or Vedic Astrology is practiced) they do use the sidereal zodiac for Astrology. This is not the place to go into the differences and pros and cons of the two. My point is simply that Astrologers are aware of the difference, even if your teachers are not.

The key difference is that because of a 'wobble' in the Earth's rotation on its axis the position of the Sun at the March equinox, varies by a degree every 72 years, moving in a direction against the order of signs. So the stellar backgound at the March equnox is now in the constellation of Pisces. This phenomenon is called the precession of the equinoxes. In effect there are two alternative systems of measuring the start of the 'circle' of the zodiac and both are equally valid. One is based on the constellations, the other is based on Earth's seasons. As Astrology is geocentric in it's interest (yes Astrologers do know that the Earth orbits the Sun) it is the perception of the zodiac on Earth which is taken as more important.

You wil find several threads that look at the topic here. It's quite a hot topic. I've tried to keep things simple for you, given that English is not your first language (though I was impressed with your post). It's possible to get more technical and more precise but the essential point is there. As you learn more of both Astronomy and Astrology you will learn that there is much valid debate around the issue.

So tell them that Astrologers use signs not constellations (signs being equal 30 degree segments of the zodiac) and that Astrologers measure their signs from a unique point - the March equinox, not from a debatable point in the constellation of Aries.