You may need heard that opposition is the very best time of 12 months to watch a planet. However what’s opposition? And which planets have oppositions? In astronomy, opposition means a planet is reverse the sun. So, for instance, the planets with orbits inside Earth’s orbit (Mercury and Venus) can’t be in opposition. However the planets orbiting exterior Earth’s orbit – Mars, Jupiter, Saturn, Uranus, Neptune – all can.
As soon as every year, we cross between them and the sun in our smaller, quicker orbit. If the sun is setting within the west, and Jupiter is rising within the east, then Jupiter is at opposition. Earth is passing between the sun and Jupiter, which can, subsequently, take all evening to cross our sky. At opposition, a planet is best to watch as a result of it’s usually closest to Earth and visual all through the evening.
Take a look at the diagram above. The sun is within the middle of the diagram. Earth is a bit approach out, and Saturn farther nonetheless. As seen from above our solar system, the planets are transferring counterclockwise across the sun. Now, run this diagram ahead in your thoughts. As a result of it’s in an interior orbit, Earth travels quicker than Saturn. And Jupiter (not proven) travels quicker than Saturn. In fact, the planets shall be in varied configurations as seen from above the solar system. However, in practically each earthly 12 months, Earth will cross between the outer planets and the sun. That is opposition.
An opposition as seen from Earth
At opposition, Earth is in the midst of a line between an outer planet and the sun, and we see the sun at one finish of our sky and the opposition planet in the other way. It’s as if you happen to’re standing instantly between two pals as you chat within the grocery store, and you have to flip your head midway round to see one after which the opposite. At opposition, the sun is on the other aspect of the sky from the outer planet; when the sun units within the west, the planet is rising within the east. Because the planet drops beneath the horizon, the sun pops above it once more: reverse.
To be technical, opposition for an outer planet occurs when the sun and that planet are precisely 180 levels aside within the sky. The phrase involves English from a Latin root, that means to set towards.
Contemplate that Venus and Mercury can by no means be at opposition as seen from Earth. Their orbits are nearer to the sun than Earth’s, to allow them to by no means seem reverse the sun in our sky. You’ll by no means see Venus within the east, for instance, when the sun is setting within the west. These inner planets all the time keep close to the sun from our standpoint, not more than 47 degrees from the sun for Venus, or 28 levels for Mercury.
Oppositions can solely occur for objects which can be farther from the sun than Earth is. We see oppositions for Jupiter, Saturn, Uranus and Neptune about yearly. They occur as Earth, in its much-faster orbit, passes between these outer worlds and the sun. We see oppositions of the planet Mars, too, however Martian oppositions occur about each 27 months, as a result of Earth and Mars are so comparatively shut collectively in orbit across the sun. Their orbits, and speeds in orbit, are extra related.
Dates of upcoming oppositions
Since every thing in space is all the time transferring, oppositions of planets farther than us from the sun occur time and again. So far as the intense planets go, the following opposition is rarely too far-off:
Mars was at opposition on December 8, 2022, and shall be once more on January 15, 2025.
Jupiter was at opposition on September 26, 2022, and shall be once more on November 2-3, 2023.
Saturn was at opposition on August 14, 2022, and shall be once more on August 26-27, 2023.
Uranus shall be at opposition on November 9, 2022, and subsequent on November 13, 2023.
Neptune shall be at opposition on September 16, 2022, and subsequent on September 19, 2023.
Word that Jupiter’s oppositions come a few month later every year. Saturn’s come about two weeks later every year. Uranus and Neptune opposition dates come just a few days later, 12 months after 12 months.
Why are planets at opposition so attention-grabbing to sky-watchers?
As talked about, as a result of they’re reverse the sun, planets at opposition rise when the sun units and might be discovered someplace within the sky all through the evening.
Secondly, planets at opposition are typically close to their closest level to Earth in orbit. As a result of non-circular form of planetary orbits, the precise closest level could be completely different by a day or two, as would be the case for Jupiter in 2023. Jupiter’s opposition is on November 2-3, 2023, and its actual closest level shall be on November 1-2. Nonetheless, for a lot of weeks round opposition – between the time we cross between an outer planet and the sun – the outer planet is usually closest to Earth. At such a time, the planet is brightest, and extra element might be seen by telescopes.
And right here’s one other attention-grabbing side of opposition. For the reason that sun and outer planet are instantly reverse one another in Earth’s sky, we see that far-off planet’s absolutely lit daytime aspect. Totally lit planets seem brighter to us than ones not utterly lit. When you’re saying to your self that this sounds so much just like the moon, you’re proper! In spite of everything, what’s a full moon if not the moon at opposition? Through the moon’s full phase, it’s instantly reverse the sun within the sky, absolutely illuminated, and at its brightest for that orbit. Because it strikes by the remainder of its orbit, the sun-Earth-moon line bends and provides us what we see from Earth as the moon’s phases.
Oppositions from different planets
Like a lot in life, opposition is all about standpoint. We’ve been speaking concerning the view from Earth. What if we flip it round?
When an outer planet – let’s say Jupiter – is at opposition for us, Earth is at inferior conjunction as seen from that planet. In different phrases, in the intervening time of opposition for us on Earth, observers on Jupiter would see Earth passing between their world and the sun. The Earth and the sun could be in the identical aspect of Jupiter’s sky, Earth hidden within the sun’s glare besides to expert observers utilizing particular gear.
Contemplate additionally that the road from the sun to Jupiter passes by the Earth, which suggests Earth passes instantly between the sun and Jupiter. Perhaps one day, a customer to Jupiter will see Earth transit the sun as seen from Jupiter. That’s, they’ll see Earth’s darkened nighttime aspect, and all of humanity, cross the face of the sun from half a billion miles away.
Backside line: The best time to watch a planet is round opposition. Throughout opposition, Earth passes between an outer planet and the sun, putting the planet reverse the sun in our sky. A planet at opposition is closest to Earth in its orbit and shiny. It rises when the sun units, and so is seen all evening.
Read more: Saturn at opposition August 26-27, 2023
Read more: Jupiter at opposition November 2-3, 2023
