Uranus at Perigee

Uranus is the Rodney Dangerfield of planets. Like most of the solar sysytem, it’s named for a character from Greek mythology, the father of Cronus and the granfather of Zeus. Unfortunately, in modern English, the pronunciation leads to scatalogical jokes, whether it’s pronounced Uran-us or Ur-anus. Ron Weasley was merely repeating generations of schoolboy humor, when sharing a telescope with Lavender Brown in Divination class, he asked, “May I see Uranus, too, Lavender?” in Harry Potter and the Goblet of Fire.  Although visible to the naked eye, Uranus was the first planet discovered with a telescope. Discovered in 1781 by Sir William Herschel, the brother of Caroline Lucretia Herschel, the mysterious blue planet is approaching perigee, when it is closest to the Earth and most easily visible to the naked eye.

Ever since Voyager 2 beamed home spectacular images of the planets in the 1980s, planet-lovers have been hooked on extra-terrestrial aurorae. Aurorae are caused by streams of charged particles like electrons, that come from various origins such as solar winds, the planetary ionosphere, and moon volcanism. They become caught in powerful magnetic fields and are channelled into the upper atmosphere, where their interactions with gas particles, such as oxygen or nitrogen, set off spectacular bursts of light. The alien aurorae on Jupiter and Saturn are well-studied, but not much is known about the aurorae of the giant ice planet Uranus. In 2011, the NASA/ESA Hubble Space Telescope became the first Earth-based telescope to snap an image of the aurorae on Uranus.

{image via NASA}

In 2012 and 2014 astronomers took a second look at the aurorae using the ultraviolet capabilities of the Space Telescope Imaging Spectrograph (STIS) installed on Hubble. They tracked the interplanetary shocks caused by two powerful bursts of solar wind travelling from the Sun to Uranus, then used Hubble to capture their effect on Uranus’ aurorae — and found themselves observing the most intense aurorae ever seen on the planet. By watching the aurorae over time, they collected the first direct evidence that these powerful shimmering regions rotate with the planet. They also re-discovered Uranus’ long-lost magnetic poles, which were lost shortly after their discovery by Voyager 2 in 1986 due to uncertainties in measurements and the featureless planet surface. This composite image (right) is constructed from information provided by Voyager 2 combined with  two different observations made by Hubble — one for the ring and one for the aurorae.

Uranus is currently in opposition to the sun, such that Uranus, the Earth, and the Sun  form a straight line with the Earth in the middle. Because Uranus is in perigee and opposition simultaneously, “Uranus will reach its lowest point in the sky four minutes earlier each night, until it gradually recedes from the pre-dawn sky whilst remaining visible in the evening sky for a few months.” To find where Uranus will be best visible in your area, consult in-the-sky.org.

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About Susan Macdonald

Susan Macdonald is the author of the children's book R is for Renaissance Faire, as well as short stories in Alternative Truths,  Swords and Sorceress #30, Supernatural Colorado, Barbarian Crowns, and Knee-High Drummond and the Durango Kid. Her articles have appeared on Krypton Radio's website, in The Inquisitr, and in The Millington Star. She enjoys Renaissance Faires (see book above), science fiction conventions,  Highland Games, and Native American pow-wows.

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