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Half of the constellations of the zodiac line up across the south as night falls this evening like charms on a bracelet. The lineup begins with Gemini, which is quite low in the west-northwest. Both the crescent Moon and Venus, the “evening star,” are within its borders. Cancer is to the upper left of the twins. Then the lineup arcs across the south to include Leo, Virgo, Libra, and finally Scorpius, low in the southeast.
In ancient times, skywatchers assigned special meaning to these constellations because they’re on the ecliptic — the Sun’s path across the sky — so the Sun moves across them each year.
Another constellation also lies along this path, but it’s not a member of the zodiac. Ophiuchus is to the upper left of Scorpius at nightfall. Its brightest members form the faint, wide-spread outline of an old coffee urn.
Ophiuchus isn’t an official member of the zodiac because the Sun doesn’t cross the urn itself. Instead, it just nips the southern edge of the modern version of the constellation, which includes a wide area around the classical outline.
All of the modern constellations have well-defined borders. That turns the sky into a giant quilt with 88 patches. They’re of many different sizes and shapes. Some are simple rectangles, but most have odd outlines to hold the classical star pictures. In fact, the border of Ophiuchus consists of 38 segments — an oddly shaped patch that just intersects the ecliptic.
Script by Damond Benningfield