Circles of the skyMason DahlAward: Top 100
School: evanston township high school At home, the city washes out stars before I can capture them. So, when the stars were visible on a vacation to the Blue Ridge Mountains, I knew it was the perfect opportunity for a star-trails photo! I pointed my camera at Polaris and set it to take 30-second slices of the sky every 40 seconds for an hour. When combined, we get a captivating spiral effect as the Earth rotates. Polaris stays near the center because it is most aligned with Earth's axis of rotation, and the other stars appear to arc around that point. This isn't actually circular motion, though, but apparent motion. This happens because the camera is rotating with the Earth, so from the view of the camera, the stars are tracing a circle in the sky, while in reality, they are still. The colors of the stars are not random. They mostly come from the surface temperature. Cooler stars appear redder/orange, while hotter stars appear bluish/white. The color is also affected by my camera; things such as white balance, exposure, and sensor sensitivity alter colors. Streaks also appear across the screen outside the pattern the stars form. Some of these are planes, satellites, and possibly a meteor. Because planes and satellites are much closer than the stars, their real motion creates a much larger apparent shift between frames. Despite seeing none of this with my own eyes, trust in time, and my camera unveiled an invisible world of physics. 
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