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View Full Version : Why is the closest point in a planet's orbit to Earth called "opposition"?



parallaxicality
2016-Sep-27, 09:21 PM
I've always been confused by that, even if there's probably a very simple explanation.

antoniseb
2016-Sep-27, 09:23 PM
Opposition (when expressed without modifiers) is when the planet is on the opposite side of the Earth from the Sun. In Astrology-speak the Sun and planet are in Opposition.

DonM435
2016-Sep-28, 12:48 AM
I know that in Chess, when the two Kings are in opposition, they're as close as they can legally approach one another. Pretty much same idea in astronomy, I'd say.

grapes
2016-Sep-28, 01:28 AM
Or, inferior conjunction

tony873004
2016-Sep-28, 02:00 AM
Or, inferior conjunction
Yes, that's for Mercury and Venus. At their closest they are not opposite the Sun. Best case scenerio, they are crossing the solar disc. For the planets external to Earth, its called opposition because as Antonisib said, they are opposite the Sun.

Jens
2016-Sep-28, 06:39 AM
I've always been confused by that, even if there's probably a very simple explanation.

So was I. My initial assumption was that it meant that the planet and earth were on opposite sides of the sky. But it actually means what Antoniseb wrote, that the planet is on the opposite side of the sky from the sun.

George
2016-Sep-28, 02:04 PM
So was I. My initial assumption was that it meant that the planet and earth were on opposite sides of the sky. But it actually means what Antoniseb wrote, that the planet is on the opposite side of the sky from the sun. Funny that I never thought of that way. Instead, probably like most, I have always picked a nice spot (mentally) where I can look below where I can picture the position of Sun and planet. I am always in the northern hemisphere, so do those down-under use look "down" from a distant southern hemisphere point?

chornedsnorkack
2016-Sep-30, 11:23 AM
Also, opposition is not the closest approach on the general case of uncircular orbits, like Mars or comets.