What do you mean when you say “the Sun is in Taurus”. I get that my star sign is Taurus, but what does that mean astronomically? I’m not talking about my personality, I’m wondering how the Sun can be in the same zodiac for a month.
Or does it have nothing to do with astronomy?
I don’t care if astrology is fake or whatever. I’m just trying to understand the expression of “a planet is in this zodical” generally.
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Imagine looking down on the solar system, with the sun in the middle and Earth moving in (roughly) a circle around it. It takes a year for that to complete.
Astronomically for the sun to be “in” a constellation you can draw a line from Earth through the sun and out into the stars. Throughout the year this will land you in different constellations, which are the 12 from the zodiac.
These constellations aren’t aligned with the ones astrologers follow since they tend to use constellations based on the day of the year, not actual star positions, which means they’re a few weeks off due to leap years.
The earth spins around on its axis each day. As it does so, the stars and the sun – which for our purposes pretty much don’t move at all during a day relative to one another – appear to move in the sky, in the same way that objects outside a moving car appear to move as you pass them. A star that is overhead at midnight, for example, will set six hours later on your western horizon. In general, the path draws out a circle in the sky centered on a point above the north or south pole, as seen in [star trail](https://en.wikipedia.org/wiki/Star_trail) photos.
Unlike the distant stars, though, the sun’s position in the sky *does* slightly change over time as the Earth itself orbits the sun. This means that while each day of the sun’s movement roughly draws out a circle the same way the stars do, that circle changes very slightly with each passing day. This change makes the time it takes the sun to trace out a circle (24 hours, a *solar* day) very slightly longer than the time it takes the stars to trace out their circle (23 hours 56 minutes 4 seconds, a *sidereal* day). In short, the sun slowly “falls behind” as it and the stars appear to rotate overhead (the Earth is really doing the rotating, but because you’re traveling with it, it feels like you’re still and the stars are moving).
If you imagine compensating for the apparent rotation of distant stars around the Earth – say, by having a telescope that rotates at the same rate, or by imagining that the Earth stopped spinning – this slow “falling behind” would instead look like the sun tracing out another, much slower circle backwards across the stars, eventually returning to its original location a year later. As it does so, it passes through 12 constellations which we call the zodiac, and because it takes a year to complete its trip relative to the stars, it stays in each of the zodiac constellations for approximately a month.
When we say “the Sun is in Taurus”, what we mean is “right now, the sun is located in the part of the sky occupied by Taurus”. After a little time, the sun will fall behind Taurus in the sky, and drift into the next constellation in the zodiac (Gemini, as it happens). This is, by the way, why you see different constellations at different times of year – the same constellations are always present, but constellations that are up during the night in winter are up during the day (and therefore not visible) in summer.
The zodiac signs are twelve constellations of stars in a circle around the sky. Depending on the time of year, the sun appears to be overlapping one of those constellations at any given time. (Also the moon, and planets, though those can change much more quickly than the sun.) So if the sun is in Capricorn, it means that from Earth, the sun and Capricorn constellation appear to be lined up. What sign the sun is in when you’re born determines your “birth sign”, AKA the one most people know and care about.
Or it *should* mean that, but astrology is dumb, and they haven’t updated the dates to account for leap years in centuries so the sun is not actually in Capricorn when Capricorns are supposedly born, or any of the signs. But it’s all made up anyway, so…
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