Hubble Captures a Rare Eclipse on Uranus

August 31, 2006
Hubble Captures a Rare Eclipse on Uranus
Credit: NASA, ESA, L. Sromovsky (University of Wisconsin, Madison), H. Hammel (Space Science Institute), and K. Rages (SETI Institute)

This image is a never-before-seen astronomical alignment of a moon traversing the face of Uranus, and its accompanying shadow. The white dot near the center of Uranus’ blue-green disk is the icy moon Ariel. The 700-mile-diameter satellite is casting a shadow onto the cloud tops of Uranus. To an observer on Uranus, this would appear as a solar eclipse, where the moon briefly blocks out the Sun as its shadow races across Uranus’s cloud tops.

Though such "transits" by moons across the disks of their parents are commonplace for some other gas giant planets, such as Jupiter, the satellites of Uranus orbit the planet in such a way that they rarely cast shadows on the planet's surface. Uranus is tilted so that its spin axis lies nearly in its orbital plane. The planet is essentially tipped over on its side. During the course of its orbit around the Sun, first one pole and then the other is alternately illuminated. As a result, Uranus has extreme seasons during its 84-year orbit around the Sun. The moons of Uranus orbit the planet above the equator, so their paths align edge-on to the Sun only every 42 years.

This transit has never been observed before because Uranus is just now approaching its 2007 equinox when the Sun will shine directly over the giant planet’s equator. The last time a Uranian equinox occurred, when transits could have been observed, was in 1965. However, telescopes of that era did not have the image sharpness required to view satellite transits on Uranus. When Hubble was launched in 1990, the Sun was shining over Uranus’s far northern latitudes. Over the past decade Hubble astronomers have seen the Sun’s direct illumination creep toward equatorial latitudes and the moons' orbits approach an edge-on configuration.

Ariel, named for a mischievous airy spirit in Shakespeare's “The Tempest,” is only one-third the size of Earth's moon. Ariel is the nearest large satellite to Uranus. As Uranus approaches equinox, there will be additional eclipses by the large moons Umbriel, Titania, and Oberon, and by many smaller moons.

Lawrence A. Sromovsky of the University of Wisconsin-Madison, Heidi B. Hammel of the Space Science Institute, Boulder, Colorado, and Kathy A. Rages of the SETI Institute, Mountain View, California, created this color composite image from images at three wavelengths in near infrared light obtained with Hubble’s Advanced Camera for Surveys on July 26, 2006.

Source: Space Telescope Science Institute

Explore further: Telescopes team up to find distant Uranus-sized planet through microlensing

Related Stories

Neptune's moon of Triton

July 29, 2015

The planets of the outer solar system are known for being strange, as are their many moons. This is especially true of Triton, Neptune's largest moon. In addition to being the seventh-largest moon in the solar system, it ...

Finding Pluto—the hunt for Planet X

July 17, 2015

Our solar system's shadowy ninth (dwarf) planet was the subject of furious speculation and a frantic search for almost a century before it was finally discovered by Clyde Tombaugh in 1930. And remarkably, Pluto's reality ...

Recommended for you

Image: Hubble sees a dying star's final moments

July 31, 2015

A dying star's final moments are captured in this image from the NASA/ESA Hubble Space Telescope. The death throes of this star may only last mere moments on a cosmological timescale, but this star's demise is still quite ...

Earth flyby of 'space peanut' captured in new video

July 31, 2015

NASA scientists have used two giant, Earth-based radio telescopes to bounce radar signals off a passing asteroid and produce images of the peanut-shaped body as it approached close to Earth this past weekend.

Exoplanets 20/20: Looking back to the future

July 31, 2015

Geoff Marcy remembers the hair standing up on the back of his neck. Paul Butler remembers being dead tired. The two men had just made history: the first confirmation of a planet orbiting another star.

Binary star system precisely timed with pulsar's gamma-rays

July 31, 2015

Pulsars are rapidly rotating compact remnants born in the explosions of massive stars. They can be observed through their lighthouse-like beams of radio waves and gamma-rays. Scientists at the Max Planck Institute for Gravitational ...

0 comments

Please sign in to add a comment. Registration is free, and takes less than a minute. Read more

Click here to reset your password.
Sign in to get notified via email when new comments are made.