What was the distance from the Deep Impact spacecraft to the moon on January 16, 2005?
On January 16, 2005, the Deep Impact spacecraft turned its cameras back towards Earth and captured some beautiful images of our Moon. To aid in calibrating the spacecraft instruments, astronomers would like to know precisely how far Deep Impact was from the moon when this picture was taken. To understand this problem better, we need to know how astronomers locate objects in the sky. Much like navigators who rely on latitude and longitude to pinpoint their location on Earth, astronomers use a pair of numbers to uniquely identify every point on the celestial sphere. These numbers are called Right Ascension and Declination. Declination is very similar to latitude measurements on Earth. We start by defining a celestial equator, which is simply an extension of the Earth’s equator into the sky. This marks zero degrees declination. The range of declination values is from -90° to +90° with +90° situated at the north celestial pole, and -90° situated at the south celestial pole. Each degree is
