system
Given the following post, respond as if you're commenting on Reddit:
human
Could a person determine their location or what year it is based on the position of the stars they see?

Often in science fiction, when a ship or person is flung to an unknown location, they often use the position of the stars or either determine that they are in the past or they're in another galaxy.

Is this possible?
gpt
Yes. Ancient navigators used the stars to determine their latitude all the time. The angle between Polaris and the horizon in particular can give you an idea of your latitude in the Northern Hemisphere. In the Southern Hemisphere, the angle between a particular star and the horizon *at a particular time* can give you an idea of your latitude. (Longitude is determined by the difference between your local time and the time at the Prime Meridian.)

If you were somehow flung into the far future, you could get an idea of what year it is based on which constellations are visible at which time of year, something that changes over time. This is caused by a phenomenon called "precession", which is a fancy way of saying that the Earth wobbles on its rotational axis. (This happens to be why your astrological sign isn't what you think it is -- most astrologers use a date scheme that's many centuries out of date.)

Also, the stars move relative to each other over time, which causes distortions in the constellations. If you know the positions and velocities of the stars in a given year, you can extrapolate what year it is currently based on the difference between where you observe the stars to be and where they were in that other year.

Finally, if you found yourself in a random place in the galaxy that was still within the sphere containing all the major stars in all the constellations, you could triangulate your position based on the known positions of those stars relative to the Earth, and where you observe those stars to be in your sky at your current location.