Long Exposure Pictures (Circular? vs. Streaks. Center Point? Always Same? What is the Star?)

Question

To an expert that can help my curiosity,

How is it the night sky becomes a circular streak of chalk like lines on a space/sky canvas on a long exposure pictures? Would it not consist of streaks following our axis rotation? I wilL ask why to this once you answer....so explain as in depth as possible please.

I have seen a lot of these pictures and I don't know the locations of all of them but I am curious what the center point coordinates? or what center star is? If it is always a circular spin on the same celestial star, what would that mean? Would that make that star our pole?? if rotation and star are consistent in all the pictures, right?

Thank you so much,

You are very much appreciated,

Answer 1

It depends on what part of the sky the camera is looking at. The Earth is spinning on its axis, so long exposure pictures taken in the northern hemisphere and including the north star Polaris will look like concentric circles if exposed long enough. The shorter the exposure time, the shorter the streaks. As the view of the camera decreases the latitude it is looking at, the arcs become "longer", they have a larger radius of curvature, and you would only see sections of each arc. If you point the camera at the sky above the equator, the streaks would look more or less parallel depending on how large the field of view has been set to.