prograde/retrograde

[prettygoodword]

retrograde (RE-truh-grayd) - adj., moving backwards, as in (astro.) moving in an orbit that is opposite a reference orbit or rotation, such as the Earth's; proceeding from last to first; contrary, conterproductive.

prograde (PROH-grayd) - adj., moving in an orbit that is the same direction as a reference orbit or rotation.


If a satellite moved east to west, opposite the Earth's rotation of west to east, it would be in a retrograde orbit. It's easier, because of angular momentum, to launch one into a prograde orbit. Retrograde is older, from Latin retrōgradus, going back, from retrō- back/backwards + gradī, to step/go. Prograde was coined in 1967 on its model.

---L.

Comments

[flwyd.livejournal.com]

Not knowing the term "prograde," I'd been using the term "anterograde" to describe the typical planetary motion (as in "Was your message received because Mercury is anterograde?")

I just looked up anterograde and realized that I'd confused moving in the same spatial direction with moving in the same temporal direction.

[prettygoodword.livejournal.com]

Heh. Yeah, ante- and anti- are sideways of each other.

---L.