An “opposition” happens on the day that Earth and an outer planet line up on the same side of the Sun. For Earth observers, a planet in opposition will rise when the Sun sets and will be in the sky all night. Around the time of opposition, the planet is brightest, practically fully illuminated, and displays the largest angular diameter for the year. Right before, during, and after opposition are prime-time for viewing and imaging a planet!
Amateur and large observatory scopes can do best when imaging planets at opposition. It was just announced this summer that amateur astronomer Kai Ly discovered an unknown moon of Jupiter while examining opposition images taken with the 3.6-meter Canada-France-Hawaii Telescope at Mauna Kea Observatory in Hawaii. This news comes just in time to take some confirmation images as Jupiter opposition season is upon us now!
Anis Abdul’s composite image of Uranus and moons is from the October 2017 opposition and was posted to his Facebook page. The imaging gear used was a Celestron Edge 11 telescope, riding on on AP900 mount, that was “amplified” with our Tele Vue 2.5x Powermate to achieve 7,000 mm focal length. Imaging was done with a ZWO ASI224MC color camera . The best 50% of frames from 20-minutes of video were processed for the image. Software used was Pixinsight and Registax.
“One of the closer moon (Miranda) is actually visible in my stacks but is lost in the planet glow ,” says Anis.
The “ice giant” planet Uranus was in opposition on October 28th. That means that the Sun, Earth, and Uranus all lined up together at an instant in time on that date. Uranus is on the same side of the Sun as the Earth, so the planet was closest to Earth and brightest for the year and in the sky all night long. If you missed it: don’t worry. The slow-moving planet will remain at least 3.7″ of arc in diameter and at magnitude 5.7 for the next month.
On the 23rd, the “ice giant” Uranus will be visible all night, as it rises when the sun sets (hence it is opposite the sun). It will also be at its largest for the year: a diminutive 3.73″ of arc. Due to its distance and close-to-circular orbit, Uranus doesn’t vary that much in brightness over time. It will reach magnitude 5.7 from mid-October through early November before slightly fading to magnitude 5.9 in late March 2019. This makes it a naked-eye target in dark skies and easy to locate in a binocular or finderscope.
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