Ophiuchans

[posted by Callimachus]

My son was born December 12. My daughter was born December 13. What zodiac sun sign are they?

If you said "Sagittarius," you're wrong. The sun wasn't in Sagittarius on those dates. The large constellation Ophiuchus dips into the zodiac, and the sun and all the planets pass briefly through it in their rounds, but ancient astrologers found it convenient to ignore this and construct a zodiac of 12 equal parts.

In the 2nd century, Ptolemy listed 29 stars in Ophiuchus. He recognised that most of those stars were north of the ecliptic (the path of the Sun through the sky); however, four of them (today known as 36 Oph, 42 θ Oph, 44 Oph, and 51 Oph) he recognized as being south of the ecliptic. Therefore, the Sun passed through the constellation of Ophiuchus as it was recognised by Ptolemy.

The reason that Ophiuchus is not a part of the western astrological zodiac is because that zodiac is defined on the basis of the sun spending an equal amount of time in twelve astrological signs starting at the vernal equinox in the northern hemisphere — this is called the tropical zodiac. There is also a sidereal zodiac, which is based on the actual location of the stars in the sky, and which is used by Hindu and some Western astrologers. At present, the sun is in Ophiuchus from November 30 to December 17.

So, as a parent of two Ophiuchans, I've decided to start advocating for equal rights. I think I'll start with a song:

"Oh you know Leo and Cancer and Virgo and Sagittarius
Pisces and Ares and Taurus and Aquarius
But do you recall
The most famous zodiac sign of all?

Ophiuchus the forgotten sun sign
Had a very obscure ecliptic
Ophiuchus the forgotten sun sign
You could even call it cryptic"