by Case » Sun Apr 23, 2017 3:25 pm
Jim Armstrong wrote:I am wondering why the Earth and Moon don't show any phase in the pix, i.e., they seem to be "full."
So lets do the calculation. In the Pale Blue Dot photo, the Earth is only 0.12 pixels in size, per Wikipedia description. You’re seeing it already at least 8 times enlarged.
In the Cassini image, the best tool to use is the distance Earth-Moon. 65 pixels in the pixel-doubled zoom image. On April 12, 2017 at 10:41 p.m. PDT, the angle between Saturn and the Moon was 41.4°, as seen from Earth. The Earth-Moon distance at that time was 401242 km (249320 mi). Because of the angle, it would look shorter (× sin α) from a Saturn vantage point: 265346 km (164878 mi). 65 pixels equals 265346 km, then 1 pixel equals 4082 km (2537 mi). The earth diameter is 12735 km (7913 mi), so 3 pixels. The Moon would be 0.85 pixel. Even besides optical effects, you couldn't see phases.
[quote="Jim Armstrong"]I am wondering why the Earth and Moon don't show any phase in the pix, i.e., they seem to be "full."[/quote]
[float=left][img]http://i.imgur.com/gtzcVuy.png[/img][/float]So lets do the calculation. In the Pale Blue Dot photo, the Earth is only 0.12 pixels in size, per Wikipedia description. You’re seeing it already at least 8 times enlarged.
In the Cassini image, the best tool to use is the distance Earth-Moon. 65 pixels in the pixel-doubled zoom image. On April 12, 2017 at 10:41 p.m. PDT, the angle between Saturn and the Moon was 41.4°, as seen from Earth. The Earth-Moon distance at that time was 401242 km (249320 mi). Because of the angle, it would look shorter (× sin α) from a Saturn vantage point: 265346 km (164878 mi). 65 pixels equals 265346 km, then 1 pixel equals 4082 km (2537 mi). The earth diameter is 12735 km (7913 mi), so 3 pixels. The Moon would be 0.85 pixel. Even besides optical effects, you couldn't see phases.