It was 1AM and the stars were twinkling wildly above the Bighorn Mountains. Twinkling (also known as scintillation) is caused by the earth's atmosphere bending or refracting starlight. Planets do not twinkle because they are not a pinpoint source of light. The effect is most noticeable on nights with strong winds and differing air temperatures in the upper atmosphere. The wind chill on this night at 7,000 feet was far below zero Fahrenheit. In the center of the photo is Sirius, the brightest star in the sky. It is visible from anywhere on earth except for the very northern Arctic. Sirius is known for twinkling a rainbow of colors when it first rises. On the upper right is the constellation Orion with the bright band of the winter milky way to the left.