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TOPIC: Uranus


L

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Uranus rings
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A British scientist has said that he will attempt to debunk the view that the rings around the Planet Uranus were discovered in 1977.
In a paper being presented at the National Astronomy Meeting in Preston from April 16 to 20, Dr Stuart Eves of Surrey Satellite Technology Limited has claimed that the Uranus rings were discovered in 1797 and not 1977.
According to Dr. Eves, the discoverer of Uranus-Astronomer Royal, Sir William Herschel, gives a description of a possible ring around the planet in a paper presented to the Royal Astronomical Society in 1797.

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1986 U 2R
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A new name has been accepted by the IAU for the inner ring, 1986 U 2R, of the Uranian system discovered by the Voyager spaceprobe in 1986
IAUC 8826.

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RE: Uranus
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It was twenty one years ago today that the space probe Voyager 2 made its closest pass to the planet Uranus. This stunning achievement did more than merely free us from the shameful ignorance that characterized the pre-Uranus era; it also provided hope to a whole generation of astronomers who would never again be stifled by terrestrial methods of observing this great celestial body.

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L

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New Names for Uranus Rings
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The following names have been approved for rings of Uranus:
Mu (for R/2003 U 1)
Nu (for R/2003 U 2)
Lambda (for 1986 U1R)

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RE: Uranus
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Astronomers at the University of Wisconsin-Madison used NASA's Hubble Space Telescope to take
images of a dark spot on Uranus. The elongated feature measures 1,700 kilometres by 3,000 kilometres.

URANUS
Expand (586kb, 3000 x 2400)
Credit: NASA

This three-wavelength composite image was taken with Hubble's Advanced Camera for Surveys on August 23, 2006. The research team found the dark spot again on August 24. The inset image shows a magnified view of the spot with enhanced contrast. Uranus's north pole is near the 3 o'clock position in this image. The bright band in the southern hemisphere is at 45 degrees south.

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Liquid Water Oceans in Ice Giants
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Title: Liquid Water Oceans in Ice Giants
Authors: Sloane J. Wiktorowicz, Andrew P. Ingersoll

Aptly named, ice giants such as Uranus and Neptune contain significant amounts of water. While this water cannot be present near the cloud tops, it must be abundant in the deep interior. We investigate the likelihood of a liquid water ocean existing in the hydrogen-rich region between the cloud tops and deep interior. Starting from an assumed temperature at a given upper tropospheric pressure (the photosphere), we follow a moist adiabat downward. The mixing ratio of water to hydrogen in the gas phase is small in the photosphere and increases with depth. The mixing ratio in the condensed phase is near unity in the photosphere and decreases with depth; this gives two possible outcomes. If at some pressure level the mixing ratio of water in the gas phase is equal to that in the deep interior, then that level is the cloud base. Alternately, if the mixing ratio of water in the condensed phase reaches that in the deep interior, then the surface of a liquid ocean will occur. We find that Neptune is both too warm (photospheric temperature too high) and too dry (mixing ratio of water in the deep interior too low) for liquid oceans to exist at present. To have a liquid ocean, Neptune's deep interior water to gas ratio would have to be higher than current models allow, and the density at 19 kbar would have to be ~ 0.8 g/cm^3. Such a high density is inconsistent with gravitational data obtained during the Voyager flyby. As Neptune cools, the probability of a liquid ocean increases. Extrasolar "hot Neptunes," which presumably migrate inward toward their parent stars, cannot harbour liquid water oceans unless they have lost almost all of the hydrogen and helium from their deep interiors.

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RE: Uranus
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Uranus120906Uranus-2006-9-12-0h20m
The Planet Uranus
Exposure Time 15 seconds
Date 00:03 UTC 12 September 2006


-- Edited by Blobrana at 15:27, 2006-09-18

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This NASA Hubble Space Telescope 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 centre 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.

2006-42URANUS
Exand (78kb, 800 x 799)
Credit: NASA, ESA, L. Sromovsky (University of Wisconsin, Madison), H. Hammel (Space Science Institute), and K. Rages (SETI)

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. The moons of Uranus orbit the planet above the equator, so their paths align edge-on to the Sun only every 42 years. This colour composite image was created from images at three wavelengths in near infrared light obtained with Hubble’s Advanced Camera for Surveys on July 26, 2006.

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The observing window for Uranus is from Aug. to early Dec. 2006. The planet is at opposition in Aquarius on 5 Sep. 2006. It shines around +5.8 magnitude and its apparent diameter is 3.7". Uranus is a gas giant which is severely tipped on its axis (98 degrees tilt). This tilt means that at various times in its 84-year orbit, different regions come to view. This year the Southern Hemisphere Equatorial region is angled towards Earth. This allows for unique observing challenges with various level of equipment.

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Astronomers suspect both rings owe their blue colour to subtle forces acting on dust in the rings that allow smaller particles to survive while larger ones are recaptured by the moon.

"We know now that there is at least one way to make a blue ring that doesn't involve plumes, because Mab is surely too small to be internally active" - Mark Showalter, SETI Institute.

Showalter and astronomer Jack Lissauer of NASA Ames Research Centre in Mountain View, California, discovered Mab in Hubble Space Telescope images in 2003.

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