[X] My Assistant

[ncc1701d]

What do NASA scientists use for the "origin of longitude" when calculating orbits for Spacecraft that orbit Venus?
I assume they use the Venus Equator for the "reference plane" but what else do they use to get the "Longitude of asscending node" ?

According to Wikopedia for a geocentric orbit around earth they use earths equator as the reference plane and the "First Point of Aries" as the "origin of longitude"

My interest is in orbits around Venus though and finding the the "Longitude of asscending node" so I need to know what they use for "origin of longitude".
thanks.

[djellison]

http://lmgtfy.com/?q=origin+of+longitude+venus&l=1

The map coordinate system used for measuring longitude on Venus is different from that used on Earth. On Earth, longitude (an imaginary line stretching from pole to pole) is measured from a starting point (the prime meridian) at Greenwich, England (near London), toward the east and toward the west with increasing values in degrees until east meets west at the 180-degree point (the dateline), which is diametrically opposed to Greenwich. On Venus, longitude is measured from 0 to 360 degrees with the prime meridian centered within a small impact crater named Ariadne, located in Sedna Planitia (see Figure 3-1). There is an arbitrary convention that determines the direction of increasing longitude on planetary bodies other than Earth: longitude shall be measured in a direction opposite to that in which the planet rotates. Because Venus rotates in a clockwise direction as viewed looking down on the north pole, longitude on Venus increases in numerical value toward the east from the planet's prime meridian.