Rare Uranian eclipse
Ron Cowen
The Hubble Space Telescope has for the first time recorded an eclipse on Uranus. The white dot is Uranus' moon Ariel, which is 1,120 kilometers wide.
L. Sromovsky, H. Hammel, and K. Rages, NASA, ESA
By blocking the sun, it casts a shadow (black dot to right) on the planet's cloud tops.
Although eclipses frequently occur on Jupiter and Saturn, Uranus rotates tipped on its side, so the sun alternately shines on one pole or the other during the planet's 84-year orbit. Because the moons of Uranus orbit at the planet's equator, the sun seldom illuminates them directly. During the last equinox on Uranus, in 1965, no telescope was sharp enough to record an eclipse.
As Uranus approaches its 2007 equinox, astronomers expect Hubble's sharp eye to record many more eclipses by the planet's retinue of satellites.
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Letters:
This article tells us, "Because the moons of Uranus orbit at the planet's equator, the sun seldom illuminates them directly." I think what you mean is that the moons seldom pass directly between Uranus and the sun. But surely the sun still illuminates them, even when they're not casting shadows on the planet.
Gregory Kusnick
Seattle, WA
References:
2006. Hubble captures a rare eclipse on Uranus. Space Telescope Science Institute press release. Aug. 31. Available at http://hubblesite.org/news/2006/42.
From Science News, Volume 170, No. 11, September 9, 2006, p. 166.
