Do I See the Same Stars Every Night?

"When I look into the sky and see the stars in sort of a 2D plane, disregarding for now the depth or closeness of these stars, are they visible from my point of view every night? In Virginia, if I were to look into the sky at a certain time every night would I see the same stars?" -  Question posed by Trent .

If you can imagine hovering in space without the Earth or the Sun in the way, you'd see the same stars in the same configuration whichever direction you looked in, which ever time you looked in it. The stars do move in relation to each other, but not so much that we can notice a change over the course of a human lifetime.

Sitting here on the surface of the Earth, however, the stars do appear to move: they march across the sky every night. They continue their journey* during the day too, but we can't see them due to a combination of the brightness of the Sun and the scattering effect of Earth's atmosphere. If we could switch off the Sun for a bit we'd see the stars moving across the sky and getting back to their original starting point with a regularity that we could set our watches by.

The thing we do set our watches by, however, is the regularity of the Sun's procession across the sky, allowing for seasonal changes in day length caused by axial tilt. This has given us our 24-hour day**. The thing is, the Earth rotates relative to the stars once every 23 hours and 56 minutes. This means that if you look at the stars one night, and then go out at the same time the next day - that is exactly 24 hours later - you're actually four minutes late as far as the stars are concerned (or they're four minutes early from your point of view). Four minutes a night doesn't sound like much, but that equates to two hours over the course of a month, and an entire day from one year to the next.

This is why, for example, you and I (in the Northern Hemisphere) can only appreciate the magnificence of Orion the Hunter during the winter months: the rest of the time, due to this difference in timing between a solar day and a star-based ("sidereal") day, Orion is only above the horizon during daylight hours, where it's outshone by the Sun.




* Or, rather, we continue our journey of rotation beneath them. But these things are relative, aren't they?
** Which isn't perfect, as we have to introduce misnamed 'leap years' every now and then.

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