How does Polaris (North Star) remain the center of star trail photos?


When you take a long exposure photo of the sky at night, the result is many circular trails of light surrounding a central star (Polaris). I still can’t wrap my head around how this seemingly remains a constant with all the different orbital motions (spin, rotation, tilt, wobble) that earth is continously going through.

I know it’s said that Polaris hasn’t *always* been the North Star or center of rotation in the sky, and that it supposedly shifts over many hundreds of years. But, how is it possible to remain constant for *any amoung of time* with us spinning around a wobbling axis at around 1000 MPH, while we rotate around the sun, and the entire solar system is rotating? Shouldn’t that mean there are three different axises of rotation and the center of any star trail photo would be changing daily if not minute-by-minute?

I have also heard that this phenomena remains constant because the stars are just *too far* away (trillions of miles) for the movement to be discernable/ noticable.. which makes even less sense to me. -If you attached a laser pointer to a gently rotating, wobbling object, and aim it at a very close surface, the amount of movent of the beam on the surface might be very minimal/ negligable. But, if you aim it at a very distant surface (trillions of miles away) the amount of movent will be exponentially more significant. The same should be true for a fixed camera lens perspective, especially over the course of hundreds of years.

So I guess what I’m saying is; how does our axis of spin continuously align with Polaris while that axis is also on a wobble, and that wobbling axis of earth is rotating within an also-rotating solar system, AND while everything in the cosmos is constantly expanding?

In: 3

The axis wobbles a tiny amount. Polaris is the largish star closest to being in the right place, today. Over the centuries, it will wander off and another star will be best.

Polaris isn’t a special star, it’s just nearest to a special place.

When a wheel spins, what part of the wheel remains stationary?

The center.

To put this in more general terms, in a spinning perspective, anything sitting along the axis of rotation will not appear to move. We on Earth are a spinning perspective. The star happens to be in line with the axis of rotation.

The Earth’s axis is pointed directly at Polaris. If you stood at the North Pole, Polaris would be directly over your head, all the time.

The confusion you might have is that the tilt of Earth’s axis does *not* change over the course of a year. As the Earth orbits the Sun, the poles continue to point in the same direction. And that of course is why we have seasons, because in January the North Pole’s tilt is pointed away from the Sun and in July it’s pointed toward the Sun.

The axis does “wobble,” in that it spins around like a top losing its momentum, but this effect happens over many thousands of years, and is almost unnoticeable within a human lifetime.

Have a friend stand directly in front of you, and wave a stick back and forth. The tip of that stick is going to swing wildly from one edge of your vision all the way to the other.

Now have them stand at the opposite end of a football field from you, and wave the stick. The tip of the stick will barely be moving at all now, and will pretty much always be in the same area of your field of view.

Now have them stand approx 2,000,000,000,000,000 miles away, roughly the distance to Polaris. They could be swinging the stick back and forth miles at a time and it would still be absolutely stationary as far as you’re concerned, because it’s such a small portion of your field of vision that motion doesn’t even make a difference anymore.

It’s because earth’s axis (line through the center of the earth about which it rotates) from out of the North Pole is pointed at it (roughly….there is a small degree of error). If you were on the geographical North Pole and looked up, it would be almost exactly overhead.