Astronomy Fun Fact #93
I don't believe in astrology, but I know that there are people who do, and I want those people to know how their signs are assigned.
The Sun isn't moving much (in the rest frame of the solar system), but it does look like it moves a lot from Earth's surface. As the Earth rotates and orbits around the Sun, it looks like the Sun passes through different constellations on the sky.
For example, when the Earth is on one side of the Sun in January, the constellation Capricornus is directly behind the Sun. But when the Earth is on the other side of the Sun in July, the Sun is blocking the constellation Cancer. So your Sun sign is determined by the constellation that the Sun is blocking whenever you're born.
Of course, that's just your Sun sign. People who get really into astrology also pay attention to the positions of the Moon and planets at the time of their birth. Nearly every object in the solar system sits on one plane (kind of like the solar system is a pancake with the Sun at the center and all of the planets are sitting on that pancake). That means that every object in the solar system appears to pass through the same constellations as the Sun as they go about their orbits.
So whether or not you believe in astrology, at least you now understand how the signs are assigned.