Apogee and perigee (w-0917-03)

In gallery: Photos of the month (2007)
Related photos: Astronomy Moon

The moon is imaged here as a double exposure on a single piece of slide film on two different days in the year. This shows the difference of apogee (when the moon is farthest from Earth and appears smaller) and perigee (when closest and appearing larger). The difference in distance is due to the moon's slightly elliptical orbit around Earth. At perigee the moon appears about 10% larger than at apogee. Sometimes perigee occurs at full moon, so some full moon nights are brighter than others. A full moon at perigee and a full moon at apogee occur about 7 months apart.

The photo was made as a double-exposure with a Nikon FE, through an 8-inch Schmidt-Cassegrain telescope with focal reducer. The moon at apogee at left was photographed on April 2; the moon at perigee at right was photographed on 25 October. Between exposures the camera was carefully kept in the refrigerator in a zip-top bag.