My Libra Birthday Disappointment

My birthday is October 9.

That makes me a Libra.

I do not attach any particular astrological significance to this fact, but when I first became interested in finding constellations in the night sky, it seemed to give me one useful piece of astronomical information.

Surely, I thought, Libra ought to be visible around my birthday.

After all, I reasoned, that is what it must mean to have a birthday in Libra.

So, around my birthday, I remember asking someone who knew the night sky where Libra was.

I expected the answer to be a direction: south, perhaps, or low in the west.

Instead, I was told that Libra was with the Sun.

That answer puzzled me at first.

If there was one time of year when I ought to be able to walk outside, look up, and find Libra, surely my birthday should have been it.

But that was exactly the problem.

The traditional zodiac associates a time of year with the part of the sky where the Sun appears. If the Sun is in the part of the sky associated with Libra, then Libra is in roughly the same direction as the Sun.

And that is precisely the wrong direction to look for a constellation at night.

Libra was difficult to see at night on my birthday not despite being my zodiac constellation, but because it was my zodiac constellation.

The constellations that dominate the night sky are generally those on the other side of the celestial sphere from the Sun. Six months later, when the Earth has traveled halfway around its orbit, the situation is reversed. The part of the sky that had been hidden in daylight now occupies the evening sky.

This was a small disappointment, but an important lesson.

There are really two skies that people carry around with them.

First, there is the conceptual sky. This is the sky of ideas rather than observation: the zodiac, the seasons, the months, the names of constellations, and all the associations we have learned from calendars, books, newspapers, and culture.

Then there is the physical sky.

This is the sky you actually encounter when you walk outside.

It is not abstract or symbolic. It is specific. It depends on the exact date, the exact hour, and your exact location on Earth. At any given moment, some constellations are above the horizon, and others are below it. Some are hidden in daylight. Some have just risen. Some are about to set. And some are placed perfectly for you to look up and recognize them.

The Star Almanac is concerned with that second sky.

My failed search for Libra eventually led me to a much more useful question than, “What constellation belongs to this time of year?”

The question is:

What can I actually go outside and see tonight?