The astronomical phenomena of a planet moving into opposition isn’t unique—but what is unique is when three planets are in opposition in quick succession. This spring, the three bright outer planets—Jupiter, Saturn, and Mars—will be at opposition during a span of just 79 days.
Images courtesy of NASA/JPL-Caltech/Space Science Institute/Cornell
Jupiter’s opposition occurred first, on May 8, in the constellation Libra. Next was Saturn’s opposition, which occurred on June 27, just above the Teapot stars of Sagittarius. Finally, the opposition of Mars will take place on July 27. As if this quick three-fer weren’t enough, the 2018 Martian opposition will be the best for the next 15 years—it will be high in the sky and (relatively) massive in diameter.
Opposition occurs when two celestial bodies (like planets) appear in opposite directions in the sky. The moon, when full, would be considered in opposition to the Sun, with the Earth between them. A planet with an orbit farther from the Sun than Earth’s (like our three mentioned above) is in opposition when Earth passes between it and the Sun. This is important to astronomers because the opposition of a planet is a good time to observe it, because the planet is at its nearest point to the Earth and in its full phase. The inner planets, Venus and Mercury, can never be in opposition to the Sun from the Earth because we are outside their orbital paths.
For the people of Earth, the planetary opposition of Mars is the best time to observe and get photos because of its closeness. With Jupiter and Saturn, their relative proximity doesn't help us a great deal, because they are so far away that the closeness doesn't dramatically affect how large they appear. What opposition does for Jupiter and Saturn is to improve the opportunity that observers have to see them. When a planet is at opposition, it's up all night long, so you have a lot of dark sky time to observe it every night.
As an amateur astronomer for 25 years, I’ll be outside observing on these nights—and most definitely imaging them. I’m going to toss out some recommendations for viewing these planets here.
- Since we’re dealing with planets, you’re going to want to use a telescope, because they’ll just appear as bright stars when viewed through binoculars or spotting scopes.
- Keep the magnification low—no more than 20x-30x, depending on the aperture and focal length. This is because while bigger is sometimes better, that’s not the case with planetary observations.
- Get a set of planetary filters… these will screw onto your eyepieces or diagonal and highlight features for better views and images—and remember that they can be stacked, so don’t limit yourself to just one at a time. You may also want to grab a light-pollution filter, as well, if you’re observing in an area with a lot of ambient surface light from buildings or street lights.
- Since planets are relatively close (as opposed to stars and nebulae), they will move quickly, so a motorized and/or GoTo mount will be better than a manual one.
- If you’re planning on imaging, you’ll want to grab an equatorial mount to avoid field rotation during those long imaging sessions, although an alt-azimuth will work in a pinch if you keep your exposures fast (like around a second or less).
I know planetary opposition isn’t as exciting as the total solar eclipse last year, but this gives us a great opportunity to observe and image three of our Solar System neighbors in a very short amount of time. So, grab your gear, and get out an observe… leave your experiences below and we’ll discuss all things nerdy and astronomic!
For additional exciting reading about the Red Planet, and more, click here to be linked to the B&H Mars Opposition page!
