Astronomy Essentials

Opposition: A definition for stargazers

Chart showing opposition and conjunction.
During opposition, an outer planet or other solar system object is opposite the sun in Earth’s sky. During a conjunction, an outer planet or other solar system object is on the far side of the sun from Earth. Chart via John Jardine Goss.

What is opposition?

When a sky object is opposite the sun in our sky, astronomers say it is in opposition to the sun. The object can be an outer planet, such as Mars, Jupiter, Saturn, Uranus or Neptune. It can also be a dwarf planet such as Pluto, or an asteroid, such as Vesta. Opposition is an important event for stargazers. When it’s opposite the sun, an object rises at sunset and sets at sunrise. And it’s visible in the sky all night. So the word opposition signals the best time to observe many of the brightest and most interesting night sky objects, our sibling worlds in this solar system.

For example, when Jupiter is at opposition, the sun, Earth and Jupiter are all in a straight line, with Earth being the middle object in the line. Not only is Jupiter in a good observing location during opposition, but it’s also at its brightest and closest to Earth. The same is true for Mars, Saturn, Uranus, Neptune … and so on.

Bottom line: Opposition is when an object is opposite the sun in our sky. It’s a great time for stargazers to observe an object because it rises at sunset, sets at sunrise, and is visible all night.

Read our top tips for planet observing

January 15, 2022
Astronomy Essentials

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