12 January 1007

I know this has been done before. Now it has been done again.

I wanted to see for myself the difference in the size of the Moon at apogee and perigee.

	Apogee	Perigee
Date Time	10Jan07 1627 UT	28Dec06 0149 UT
Distance	404,334 km	370,320 km
	Last Quarter Moon	First Quarter Moon
Date Time	11Jan07 1245 UT	27Dec06 1448 UT
Angular Size	29'30"	32'34"
Size Difference	10.40% %D = ((P - A) / A ) * 100
Photo Date Time	10Jan07 1030 UT	27Dec06 2224 UT
Predicted Angular Size	29'56"	32'46"
Size Difference	9.47% %D = ((P - A) / A ) * 100
Observed Moon Diameter	186 pixels	204 pixels
Size Difference	9.68% %D = ((P - A) / A ) * 100

Both images were made with a Minolta X700 SLR camera with a 500mm f/8 catadioptric lens. Exposure for the first quarter Moon was based on the Sunny 16 rule - f/8 @ 1/125s - since the Moon is in bright sunlight, and was not adjusted in Photoshop. I made a series of hand-held exposures of the last quarter Moon at varying shutter speeds and used the image that was sharpest and adjusted it in Photoshop to match the first quarter image.) I chose this equipment because it is the only camera I have that has a fixed focal length telephoto lens. I wanted the fixed focal length lens so there would be no question of how far a zoom lens was zoomed for each picture no matter when those pictures were made.

The negatives were developed and scanned directly to photo CD.

The first quarter picture had to be straightened to get the terminator vertical before it could be used. The images were opened as layers in Photoshop and aligned on a horizontal line then the images were cropped to get a rectangular black sky. This insured that the size of the Moon did not change by dealing with each image separately. The area containing the dark side of the last quarter Moon was deleted. The layers were positioned next to each other. The image was cropped a final time to get the most information onto this page.

The image was opened in MS Paint so I could get screen coordinates to measure the diameter of the Moon in pixels. The last quarter picture, being hand held at 500mm and a slow (for that lens) shutter speed, is soft so the diameter of that Moon is not as accurate as that of the first Quarter Moon. There will not be another last quarter apogeean Moon this year to reshoot that picture.