科學圖說

角山星軌(Jiaoshan Star Trails)

利用攝影的手法，讓古老的長城和星軌結合。星軌是因為地球自轉所見亮星在天空運動的視覺軌跡，恒星仿似繞行地球以圓形軌跡旋轉，旋轉一周約需23小時56分鐘，最終回到最初的位置，這個週期稱為恒星日。如果抬頭仰望天空中的恒星，會發現它們在夜空中移動，靠近兩極的恒星會產生最小的圓，而靠近地球赤道的恒星則會產生最大的圓。恒星就像白日裡的太陽，每晚從夜空東邊移動到西邊，每小時大約向西移動15度。星軌其實是圓弧或者部分的圓，隨著時光的流逝，永不停歇地轉圈移動。

Special photography methods were used to create this image of the Great Wall and star trails, which are the trajectories of the apparent motion of bright stars in the night sky due to Earth’s rotation. These stars appear to orbit the earth. After 23 hours and 56 minutes, the time needed to complete one rotation, the stars appear again in the same position in the sky. This is referred to as sidereal day. If you stare at the stars, you will see them move across the sky. Those near the poles produce the smallest circles, while those near the equator produce the largest. Stars are like the sun in that they first appear in the east and move westward about 15 degrees every hour. Star trails form an arc or a partial circle over time.