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Once every 42 years, the angle between Uranus and the Earth is perfectly lined up so that the planet’s rings are seen edge on. Since the rings were only discovered back in 1977, this is the first opportunity astronomers will have to view the planet without the glare and dust from the rings. It doesn’t happen on a specific date, though, it’s a little more complicated than that.
Because the Earth goes around the Sun much more quickly than Uranus, there are actually three separate times that Uranus and the Earth line up perfectly: May 3 and August 16 in 2007, and then February 20 in 2008. Unfortunately, during that last point, the Sun will be directly in between our two planets, so we won’t be able to see Uranus.
The first to image Uranus during this special occasion was a team of astronomers from UC Berkeley. They imaged Uranus on May 28th with the near infrared camera and adaptive optics on the W.M. Keck II telescope atop Hawaii’s Mauna Kea. Their images revealed the nearly edge on ring appearing as a bright line passing right through Uranus.
The next images come from Hubble, taken on August 14th. Hubble captured its images on nearly the precise moment when the rings were aligned with the Earth, showing similar features to the Keck image, and also seeing some recently discovered outer rings. The outermost ring, seen by Hubble, is difficult to view in infrared.
Astronomers are hoping these images will reveal more details about the moons that help tend the ring, called Cordelia and Ophelia, keeping it in place. But it’s also thought that there are additional moons in the region, helping to tend all 9 rings. This precise geometry might allow the telescopes to reveal moons that would normally be lost in the glare of the rings.
One other important date:
“December 7 is the Uranian equinox, when the rings are perfectly edge-on to the sun, and after that, there is a brief period again when we will view the dark side of the rings, before they become illuminated again for another 42 years,” said Heidi B. Hammel of the Space Science Institute in Boulder, Colorado.
Original Source: UC Berkeley News Release