What are star trails? They are the continuous paths created by stars, produced during long time exposure photographs, as shown on this page. In other words, the camera doesn’t track along with the stars’ apparent motion as night passes (actually caused by Earth’s spin under the sky). Instead, the camera stays fixed, while, as the hours pass, the stars move. The resulting photos show the nightly movement of stars on the sky’s dome.
Star trails are actually a reflection of our planet Earth’s rotation, or spin, on its axis. The Earth rotates full circle relative to the backdrop stars in a period of about 23 hours and 56 minutes. So, as seen from Earth, all the stars go full circle and return to the same place in sky after this period of time, often referred to as the sidereal (stellar) day.
What this means is that, if you are standing out under the stars, you see them move across the sky as night passes. Stars near the celestial poles produce the smallest circles while those near the celestial equator produce the largest. The stars – like the sun during the daytime – move from east to west across the sky each and every night. Each and every star moves nearly 15o westward in one hour.
Star trails are really arcs, or partial circles, whose ever-circling motions forever tabulate the great passage of time.
Bottom line: Star trails are the continuous paths created by stars, produced during long time exposure photographs, as shown in the photos on this page.