The icy moon Ariel (white) casts a shadow on the cloud tops of Uranus - the moon is named for a mischievous spirit in Shakespeare's The Tempest (Image: NASA/ESA/l Sromovsky/H Hammel/K Rages/U Wisc/Space Science Institute/SETI Institute)
Posted on 09/02/2006 3:19:24 AM PDT by Virginia-American
A tiny moon has been caught floating in front of Uranus for the first time, the Hubble Space Telescope reveals. The moon's shadow can also be seen on the planet's cloud tops, creating a solar eclipse on Uranus itself.
Hubble imaged the event unexpectedly in July 2006, during a set of observations meant to study the planet's clouds. "When we first got this image back, we looked at it and said, 'What's that bright spot and that dark spot?'" says team member Heidi Hammel of the Space Science Institute in Boulder, Colorado, US. "We thought, it must be a problem with the detector."
Then, recognising that it resembled "transit" events seen fairly frequently around other giant planets, such as when Jupiter's moon Io passes in front of that planet's disc, the researchers realised they had seen the first ever transit on Uranus. It featured the 1130 kilometre-wide (700 mile-wide) Ariel, one of the planet's 27 moons.
The events are so rare because Uranus, unlike the solar system's other planets, is tilted almost completely on its side, with its rotational axis lying nearly in its orbital plane.
Its moons, however, orbit the icy giant above its equator. So when either of Uranus's poles is facing the Sun during the planet's 84-year orbit, the moons do not cross its disc at all as seen from Earth. Instead, they circle it on orbits that resemble the rings around a bull's eye.
Rare chance
Uranus, its moons and the Sun are only in the right alignment to observe the effect every 42 years. Now, Uranus is approaching such an ideal viewing period – it will reach its equinox, in which the Sun will shine directly over the planet's equator, in 2007. "This is a once-in-a-career event for most of us," Hammel told New Scientist.
It is also the first time in the history of astronomy that such observations are even possible. When the planet's equinox last occurred, in 1965, existing telescopes were simply not powerful enough to resolve the transits. Even today, only two or three telescopes can image them, including Hubble.
"This planet and its system of rings and moons and magnetic fields are so far away, we need the biggest and best telescopes on Earth to do a lot of the observations," Hammel explains.
In fact, the planet is so far away that even the best telescopes do not have vision sharp enough to determine the moons' sizes simply by imaging them. "They're so far away, they're just points of light," Hammel continues.
But during equinoxes, astronomers can gauge the moons' sizes by observing the moons passing in front of each other or into each other's shadows. "By looking at how long it takes for the secondary satellite to go into and out of eclipse, we can figure out the size of the first moon, which is casting the shadow," she says. Knowing the moons' physical sizes reveals their mass and clues about their history, she says.
"It's very exciting," Hammel told New Scientist. "We're really hoping we get enough telescope time to do what we need to do."
The icy moon Ariel (white) casts a shadow on the cloud tops of Uranus - the moon is named for a mischievous spirit in Shakespeare's The Tempest (Image: NASA/ESA/l Sromovsky/H Hammel/K Rages/U Wisc/Space Science Institute/SETI Institute)
Truly fabulous!
Images of Uranus .... Wow who would have thunk it.... Millions of dollars on a telescope for this simply amazing.
Amazng. I wonder if NASA can keeep the Hubble Space Telscope operating.
Uranus is blue!
Not typically !!
(( Space ping ))
A piece of Uranus where the Sun don't shine...
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Mods blew this one away a day or two ago. And the fun was just beginning.
":^/
Don't they have computer simulations that would show all of those planetary orbits, along with the moons, the attending illumination from the sun, the moons, and attendant shadows cast on the planet, etc., in full graphic representation??
My God, I would place even money I can pull up Google results that will direct me to FREE SOFTWARE that will allow me to run such a graphic program on my home computer..
How is it the Space Institute doesn't have such software?
How is it they aren't running such software on their targets in the solar system?
I would think that if someone is going to use the (darn) HUBBLE telescope to take shots of Uranus, then the first thing you do is run simulations on your (darn) computer(s) to determine what it is you SHOULD be seeing, and be able to compare it to the photographic results..
Seriously, the more I think about this the more it (ticks) me off..
Bump
That's just what they'd like you to think...
Looks like a blue marble in front of black paper to me - did this photo come from seeBS?
Yeah, I didn't get theat either. I'm sure they have ephemerides for all the planets and their satelites. I rmemeber years ago there was a somwhat similar series of eclipses of Pluto and Cahron, and they had been planned for in advance.
I am really angry with Saturn and Uranus. Neptune and Jupiter are OK though.
I thought the P.C. crowd had the name changed of Uranus ......... to Urectum.
cheese
The rings of Uranus were discovered in 1977, from observations during a stellar occultation event by astronomer teams at the Kuiper Airborne Observatory (KAO) and the Perth Observatory (Australia). Just before and after the planet moved in front of the (occulted) star, the surrounding rings caused the starlight to dim for short intervals of time. Photos obtained from the Voyager-2 spacecraft in 1986 showed a multitude of very tenuous rings. These rings are almost undetectable from the Earth in visible light.
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