Ophiuchus, the thirteenth zodiac constellation

This was a blog published this morning in my company's blog so it was first written in English.

It seems that, some days ago, the news was spreading the chaos among horoscope readers and followers saying that an american "investigator" had "discovered" a "new" zodiac constellation making the rest moving from the dates everybody thought they must be. Actually, this horoscope stuff is part of Astrology, a kind of religion that, at present, nothing has in common with the actual science, Astronomy, but the starting "astro". So, I would like to explain everyone interested what were the astronomic bases of Astrology and how this "new discovery" affect our horoscopes.

I have already explained yesterday that, at present, almost everyone accept that actually is Earth who is orbiting around the Sun and, while is turning around its own axis, make us, seeing everything from Earth surface, feel like the Sun, the Moon and the stars are turning around us. However, the ancient Greeks didn't know that. They, as many other ancient civilizations, believed that actually the earth was fixed and surrounded by a sphere, the celestial sphere, in which surface the stars was painted as shiny dots. These "dots" are in fixed positions on the celestial sphere surface so, when the celestial sphere is moving, all the stars keep the same position one respect each other. That effect leaded our ancestors to think that the stars were really grouped in so called constellations and, joining dots like a child game it was, they saw in these constellations things, animals or characters from the nature or their believes and folk. Each culture, each civilization, found in the sky different forms, different characters, different constellations, but all of them believed that they were groups of stars that were really close. Some of them, like the zodiac constellations, are very known today, at least their names.

Between the celestial sphere and Earth they thought the planets (from ancient Greek "planetai", meaning wandering star) was, stars which position was not fixed in the celestial sphere. To the Greeks, even the Sun and the Moon, since they were moving from the other stars, were planets. They also thought that, if the constellations were characters from their mythology, the planets (stars with enough power to move by themself) must be Gods. The name of the Sun and the Moon has evolved depends of the language but didn't happened the same with the rest of planets. In that way, they found 7 planets: Sun, Moon, Mercury, Venus, Mars, Jupiter and Saturn and they gave these names to the days of a week, as so we do today. To show this I must to mix English with Spanish (a Latin root language that I know very well) so sorry if you get a little lost.

Monday (in English) is the Moon Day.

Tuesday (Martes in Spanish) is the Mars Day.

Wednesday (Miercoles in Spanish) is the Mercury Day.

Thursday (Jueves in Spanish) is the Jupiter Day.

Friday (Viernes in Spanish) is the Venus Day.

Saturday (we come back again to English) is the Saturn Day.

Sunday (English again) is, as we can directly read, the Sun Day.

Actually, I don't know where your planet names came from, I suppose I must investigate a little about it for next time.

But we know that Earth and the rest of planets (we'll forget the Moon from this point) are orbiting the Sun in nearly circular orbits. If we still were thinking the celestial sphere exists but, in this case, with the centre in the Sun, we still were seeing the stars as fixed points in the night sky. Because we are moving around the Sun, the celestial sphere must be static so we can see different stars and constellations in summer than in winter. May be this is a mess for many so I'll try to explain it slowly.

"When are you going to talk about Horoscope?" Be patient, we are close.

Think in a cross like the image below. In the centre of the cross we have the Sun and at the end of each line we have the seasons: winter, spring, summer and autumn. If you are in summer and you try to see through the Sun to the celestial sphere at the other side (don't do it, you'll be blind!) you can't see any star because the bright of the Sun are hiding then at daylight, but they are there indeed. At night, you are looking to the outside of the cross, seeing the summer stars and constellations. When you are in winter and try to look to the summer constellations the Sun is in your way, blocking your line of sight.

Season Cross

So, coming back to the geocentric model (the Earth in the centre) it actually looks like the Sun is moving not only around Earth but also from the background of stars, following a path along the year called ecliptic. Because the orbits of all the planets are all of them, more or less, in the same plane as our one, from our point of view, they follow a path in the celestial sphere in the same area that the Sun does. This area, a band that fills about 8 degrees above and below the ecliptic (distances on the surface of a sphere is usually measured by degrees) is called the zodiac band. The word "zodiac" comes from ancient Greek, again, and means "wheel of animals". That was because most of the zodiac constellations are animals, like the crab, the lion, the bull or the goat.

In theory, and it was originally, Astrology used the positions of the Sun and the planets in reference to the background of stars, the zodiac constellations, to predict the future. So, if you are Aquarius that is because, in the moment of your birth, "the Sun was in Aquarius", which means that, from our point of view, if we looked to the Sun and it didn't blind us, the constellation that we'd see behind it would be Aquarius.

But, actually, the astrologists forgot to look at the sky a long time ago. They started to use tables and charts to know where the planets must be instead looking where they really are. The rules they are using have been out of date for more than 2000 years, and so they still are today. Moreover, it's very probable that the modern astrologists are using a different system than their babylonic colleagues, who first developed the astrology, mixing and integrating on their system the changes that other people were discovering in the sky but still without looking at it, just changing their charts.

For example, astronomers and astrologists set the beginning of the year on the same moment, the vernal equinox (the moment that the day and the night last the same and give the beginning of the spring in the north hemisphere), at about the 21st of March. But astrologists say that, in this day, the Sun is entering in Aries, and that's why you are Aries if you've born between about 21st of March and 21st of April. Nevertheless, currently the Sun is very inside Pisces constellation on that day making all the zodiac constellations to move about a month backward, what means that you must be the previous constellation you though you were. For example, if you were born on 25th of April, astrologists say that you are Taurus but astronomers say you must be Aries.

"Where do this difference come from?" The third movement of the Earth, the precession, produces this difference. It's not the moment to explain how it works but one the effects of this movement is that the position of the Sun at the moment of the vernal equinox is moving respect the background of stars. Every year, the Sun is in a slightly different position moving in the opposite direction at the order of the zodiac constellations, from Aries to Pisces and, in a future, from Pisces to Aquarius. But the astrologists are fixing the position of the Sun every year in the same place, the border between Pisces and Aries, since more than 2000 years ago. They, of course, are totally wrong.

“OK, that's why the zodiac constellations has been moved but, what's about the thirteenth constellation, Ophiuchus?” This is astronomically a zodiac constellation, and it was actually known by the Greeks, but it is not for astrology. The ecliptic (remember, the path the Sun draw on the celestial sphere) crosses Ophiuchus between Scorpio and Sagittarius. Also, for astronomy, the zodiac constellations have different sizes and the Sun is not spending the same time on each one. Nevertheless, astrology divides the path of the Sun in 12 regions of exactly the same size. Each region has the name of a sign (they are not constellations, they are signs) that, originally, corresponded with the constellation the Sun was expending more time in that period of time, leaving Ophiuchus out of the wheel.

Ophiuchus

As I said before, they forgot to look at the sky a long time ago and didn’t notice that, at present, the signs don’t correspond with their original constellations at all. They [the astrologist] insist in the astrology don’t follow the same pattern that the astronomy but, at the same time, they are trying to make people believe they predict the future looking at the sky. You are free to believe in what you want but, in my opinion, they must lose the starting “astro” a long time ago.

"But then, this american investigator, has he discovered something new?" No, he just said what was known for centuries. The issue was the press has made from this a very productive "new" story.

A couple of additional small differences between astronomy and astrology are:

• Exists another astronomic zodiac constellation, Cetus, the Whale, in which the Sun spends about one day.
• The names of two of the stars of Libra are “northern claw of the scorpion” and “southern claw of the scorpion” in arabic. This fact leads to think that Libra was probably added by the Romans or even introduced by modern astrology 2000 years ago as a way to made more equitable the zodiac distribution. If we take Libra as part of Scorpio and count Ophiuchus as a zodiac constellation, Scorpio would last about a month and a half and Ophiuchus only two weeks.