Tracing the star is tracing the movement of the earth. How many degrees does the earth rotate in an hour? What does the sky look like each night? Starting with these questions, I built an instrument on my balcony, which allows me to put my phone at the same place to trace the stars every night. I finally photoshopped all the star tracks together into one picture and gave each day's star track a different color; it merged into a colorful night!