I’ve always loved the night sky. It’s a shame most people don’t know what it really looks like. Of all the kinds of pollution you hear about, light pollution is rarely mentioned. Although the main sufferers are astronomers, light pollution has more bad effects than just obscuring the heavens. I can use heavy curtain to shield my home from its intrusion but I can’t banish it from outdoors. So I confine myself to books and photos and still get much enjoyment from the what’s out there and what people create from it.
Great art has been inspred by the night sky. Great science has been the result of fascination with what is suspended there. Even before what we consider modern science had evolved the night skywas studied for clues to the nature of time, the seasons and the nature of the universe. In those early explorations myths came about to create logical cosmologies in explanation of what was observed. One piece of this system was the identification of constellations.
The constellations we are most familiar with are those of the zodiac although the ancient Greeks had identified forty eight. The zodiac is an area of the sky that extends approximately 8° north or south of the ecliptic, the apparent path of the Sun across the celestial sphere over the course of the year. The paths of the Moon and visible planets are also within the belt of the zodiac. Zodiacal signs stay fixed relative to the solstices and equinoxes.
The origins of the zodiac date back to the Babylonian and Chaldean civilizations. Although the zodiac remains the basis of the ecliptic coordinate system used in astronomy, the term and the names of the twelve signs are today mostly associated with astrology. In those early times astronomy and strology were one and the same. Yet there was already a divergence.
Somewhere around the 5th century BCE, Babylonian astronomical texts began to describe the positions of the Sun, Moon, and planets in terms of 12 equally-spaced signs, each one associated with a zodiacal constellation, each divided into 30 degrees. This normalized zodiac is fixed to the stars and totals 360 degrees. The Babylonian star catalogs then entered Greak astronomy in the 4th century BC. Greek astrology derived in part from both Babylonian astrology and from Ptolemaic Egyptian astrology. The Dendera zodiac, an Egyptian relief dating to ca. 50 BC and now in the Louvre, is the first known depiction of the classical zodiac of twelve signs. There are actually thirteen constellations running along the ecliptic, the one missing from the astrological zodiac is Ophiuchus. TheBabylonians recognized it but they decided to leave Ophichus out, it would spoil the neat fit of divsions making 360 degrees and it was never a formal astrological sign.
By now astronomy and astrology have finalized their divorce. If you want to wind up an astronomer talks about astrology. Yet millions of people all over the world base serious life and business decisions on predictive astrology and in fact it once dictated the schedule and activities of the President of the United States. I find this just as fascinating as the science side of astronomy but for much different reasons, cultural ones. The psychology and mythology involved say as much about people as telescopic observations say about the universe.