Post by Chicago Astronomer - Astro Joe on Jul 26, 2006 23:51:24 GMT -6
Saturn Ring Spokes Appear Again
Pasadena CA (SPX) Jul 27, 2006
This image from the Cassini spacecraft shows a ghostly white streak, called a spoke, in Saturn's B ring. This is the first sighting of a spoke in nearly a year, and the first spoke seen by Cassini on the sunlit side of the rings. It also is the first spoke seen at high phase angle - meaning the angle formed between the Sun, the rings and Cassini.
In this geometry, the feature appears white (instead of black) against the rings because the very small particles comprising the spoke preferentially scatter light in the forward direction (i.e. toward Cassini), making the spoke brighter than the background rings.
Cassini took the clear-filter image in visible light with its wide-angle camera on July 23 at a distance of approximately 692,000 kilometers (430,000 miles) from Saturn and at a Sun-Saturn-spacecraft, or phase, angle of 115 degrees. Image scale on the sky at the distance of Saturn is 38 kilometers (23 miles) per pixel.