h2g2 The Hitchhiker's Guide to the Galaxy: Earth Edition

I'm not an astronomer, and this is probably a very stupid question, but how can I tell by looking at the night sky what sign of the zodiac the sun is passing through?

Icy

The part of the sky that the sun is in is totally blotted out by the sun's light. So the only way of telling is by noting which constellation is directly opposite the sun, and comparing with the charts.

OK, but how can I tell which constellation is exactly opposite the sun?

Well, the sun is due south at local noon, so the point opposite the sun is due south at local midnight. Just go up from the point on the horizon which is due south until you find a zodiacal constellation, then count six along the list to get the one the sun is in.

It's not really of any great interest to astronomers but the astologers think it is important. Strangely, the fact that the charts they use are all wrong doesn't worry them at all.

No, I share your opinion of astrology, but I'm fascinated by how it became established in the ancient world. It just doesn't seem intuitive to wait until midnight (as if they knew when that was without a sundial), then look due South (without a compass?), then calculate from a chart or whatever the opposite star constellation (which they couldn't see), and then consider this to be the answer to life, the universe and everything.

the fact that it was not intuitive probably added prestige to the Magi who did know how to do it.
I also do not believe in this pseudo-science, but if others want to believe, thats alright too.

I'm sure it started with plotting which planets were in the signs, and then some bright spark worked out that the stars were there behind the sun, so the sun itself must be in a star sign.

Yes, I'm sure you're both right. It's those esoteric charts which held the magic more than the night sky itself. No more scientific than tarot cards.

"And I gaze at the planets in wonder,
At the time and trouble they expend,
All to warn me to be careful
In dealings involving a friend"
- Flanders and Swann

I once had a whim and I had to obey it,
To buy a French horn in a second-hand shop.
I polished it up and I started to play it,
In spite of the neighbours who begged me to stop...

That was my favourite

Mine too.