The Best Time to View Planets: What Is Opposition in Astronomy?
Astronomical opposition is the best time to observe most of the Solar System planets and other celestial bodies. They appear at their largest and brightest state in the night sky. Find out more about oppositions and get the best dates to see planets and asteroids.
- What does opposition mean in astronomy?
- What planets can be seen at opposition from the Earth?
- How to observe a planet at opposition?
- Why are planetary oppositions interesting?
- Upcoming planetary oppositions
- Asteroid oppositions
What does opposition mean in astronomy?
Astronomical opposition means that a planet is located on the opposite side of the Earth from the Sun. From our perspective, it means a planet at opposition is precisely 180 degrees from the Sun in the sky — so, when the Sun sets in the west, a planet appears in the east. In addition to planets, an opposition can be reached by comets, asteroids, and some other Solar System objects. A well-known example of opposition is a Full Moon. During this event, the lunar disk is opposed to the Sun, therefore fully lit by the star’s light.
What planets can be seen at opposition from the Earth?
Since an opposition can only occur when the Earth is between the Sun and another celestial body, this event happens for the planets further from the Sun than the Earth. These are Mars, Jupiter, Saturn, Uranus, and Neptune.
The planets’ oppositions occur roughly every year when the Earth reaches the proper configuration with them relative to the Sun. The only exception here is Mars. The Red Planet’s orbit and orbital speed are similar to the Earth’s, so the Earth “outraces” Mars only about every 27 months. That’s why Mars oppositions occur only once in about two-three years. Mercury and Venus are located inside the Earth’s orbit, so we’ll never see them at opposition.
How to observe a planet at opposition?
To find a planet at opposition, look in the opposite direction from the sunset. The planet will be well-placed for a few weeks around the exact moment of opposition. So, check a forecast for your location, find a date close to the opposition when the skies are clear, and get outside to observe the bright planet.
At opposition, you can spot most of the planets with the naked eye, but you’ll see them even better through a pair of binoculars or a telescope. For instance, with a small 4-inch telescope, you should be able to observe Saturn’s rings, including the Cassini Division between them. To check where the planet will rise in your location and how bright it will be, use the stargazing app Sky Tonight. The app has a built-in calendar of astronomy events and a detailed map of the night sky.
Why are planetary oppositions interesting?
Opposition is the best time to observe a planet or another celestial body. At that time, objects are fully illuminated by the Sun and shine brightly in the sky. Moreover, planetary oppositions occur near a planet’s closest approach to the Earth, when a planet appears at its biggest. Mars experiences the most striking size change because it’s the closest superior planet to the Earth.
Most importantly, an opposition gives us plenty of time for stargazing! A celestial object is seen through the night and well-placed in the midnight sky. It is no coincidence that asteroids and other faint Solar System objects are often discovered at their opposition.
Upcoming planetary oppositions
Here is the list of planetary oppositions for the following months. The complete calendar of all the planetary and other celestial events is available in the stargazing app Sky Tonight.
September 16: Neptune at opposition
Neptune will reach opposition on September 16, at 21:03 GMT (5:03 p.m. EDT). The planet will shine at a magnitude of 7.81 in the constellation Aquarius; the size of Neptune’s disk in the sky will amount to 2.4 arcseconds. The planet will be too small and dim to spot with the naked eye, so it’s best to observe Neptune with a telescope or powerful binoculars.
September 26: Jupiter at opposition
On September 26, at 18:03 GMT (2:03 p.m. EDT), enjoy Jupiter at opposition. The planet will be at a magnitude of -2.94 in the constellation Pisces; its visual size will reach 48.8 arcseconds. Jupiter will be big and bright enough to spot with the unaided eye, but you can use a pair of binoculars or a small telescope for an even better view.
November 9: Uranus at opposition
Uranus will reach opposition on November 9, at 8:41 GMT (3:41 a.m. EST). See the planet shining at a magnitude of 5.64 in the constellation Aries. Its size will be 3.8 arcseconds at its largest. You can spot the planet with the naked eye, with clear skies and sharp eyes provided, but you’ll get a better view with a pair of binoculars or a small telescope.
December 8: Mars at opposition
On December 8, at 4:24 GMT (on December 7, at 11:24 a.m. EST), there will be the last and most spectacular planetary opposition of 2022. Mars (magnitude -1.87) will shine at its biggest and brightest in the constellation Taurus. The disk size of the planet will be 17.0 arcseconds. It will be well-seen with the naked eye, but don’t miss the chance to explore the Martian surface with a pair of binoculars or a telescope. Find out more about Mars opposition 2022 in our new infographic.
Not only planets but also comets, asteroids, and other Solar System bodies can reach opposition. Such events are more challenging to spot, so they are more for experienced astronomers. Here is the list of asteroids that reach opposition in the following months:
- August 22, 11:58 GMT (7:58 a.m. EDT): Asteroid 4 Vesta (magnitude 6.1), constellation Aquarius.
- September 7, 19:10 GMT (3:10 p.m. EDT): Asteroid 3 Juno (magnitude 7.8), constellation Aquarius.
- November 12, 16:46 GMT (11:46 a.m. EST): Asteroid 27 Euterpe (magnitude 8.8), constellation Aries.
- November 19, 11:58 GMT (6:58 a.m. EST): Asteroid 115 Thyra (magnitude 9.7), constellation Perseus.
- November 22, 11:58 GMT (6:58 a.m. EST): Asteroid 324 Bamberga (magnitude 9.1), constellation Perseus.
- November 29, 09:34 GMT (04:34 a.m. EST): Asteroid 30 Urania (magnitude 9.6), constellation Taurus.
- December 1, 14:22 GMT (9:22 a.m. EST): Asteroid 349 Dembowska (magnitude 9.7), constellation Taurus.
Opposition is also the best time for asteroid hunters. If you want to discover a new asteroid, it’s better to look at night in the direction opposite to the Sun, and maybe you’ll get lucky!
What planets are in opposition now?
Neptune reaches opposition on September 16, 2022. Jupiter will follow it, coming to opposition on September 26. The planets will stay well-placed for the whole month shining in the sky all night.
How often do planetary oppositions occur?
A planetary opposition occurs when the Earth passes between the Sun and a planet. It happens every year for the superior planets. The only exception is the Martian opposition. Since the planet is very close to the Earth and its orbit and orbital speed are similar to the Earth’s, our planet manages to pass between Mars and the Sun only every 27 months, so we get one Martian opposition in about two-three years.
How long does an opposition last?
A planet is said to be “at opposition” at the exact moment of time, but the period of opposition lasts for a few weeks. You can observe the planet on any convenient date around that time. It will rise on the opposite side to the Sun right after sunset, reach the highest point at midnight, and set at dawn.
What is the opposite of opposition in astronomy?
The opposite of opposition in astronomy is a conjunction. During the conjunction of a planet and the Sun, the planet is at the closest distance from the Sun in the sky. It’s the most difficult time to observe the planet because the Sun hinders the view. But there are other astronomical conjunctions that don’t involve the Sun: for instance, planetary conjunctions and lunar-planetary conjunctions. They are quite interesting to observe!
Bottom line: Opposition is the best time to observe planets because they shine at their biggest and brightest, visible all night through. The good news is that you don’t need to catch the exact moment of opposition to enjoy the view. Choose a convenient time, go away from the city lights and observe planetary oppositions in full beauty!
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