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TOPIC: Uranus


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Uranian ring plane
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On Thursday, August 16th, Earth will cross the equator and ring plane of Uranus, and astronomers all over the world will be on watch. The unusual geometry offers a unique view of the planet's atmosphere, satellites and ring system.
Because of Earth's own orbital motion, our planet actually crosses the Uranian ring plane three times in succession: on May 2, 2007, August 16, 2007, and February 20, 2008. The August event is by far the most favourable; Uranus will be less than a month from its opposition to the Sun (on September 9th), so it will be visible almost all night (in Aquarius). Another interesting fact is that December 7, 2007, is the date of Uranian equinox, when the Sun will cross the planet's equatorial plane.

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RE: Uranus
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Uranus's Orbit Eccentricity Precession, Last Million Years

[youtube=http://youtube.com/watch?v=Qimh4ZkNfJI]

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Uranus's Orbit Inclination Precession, Last Million Years

[youtube=http://youtube.com/watch?v=UesLnRnTp7Y]

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uranusneptunechart

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Uranus has no diamonds after all
Hunting for diamonds on Uranus or Neptune would be a lost cause, say the authors of a new study. Contrary to previous suggestions, these two planets do not have enough carbon to make diamonds.
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RE: Uranus Moons
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For the first time, astronomers have glimpsed one of Uranus's 27 moons passing in front of one of its siblings a fleeting alignment that can reveal information about the moons, such as their mass, that cannot be gleaned in any other way.
Researchers hope this will be the first in a bonanza of data returned from Uranus in the next year. That is because Uranus, which orbits the Sun every 84 years, is in an ideal geometry to view its moons. Such periods come around only once every 42 years, and the next will not occur until 2049.

Umbriel07

This series of pictures illustrates how Uranus's moon Oberon passed in front of the moon Umbriel on 4 May. The grey areas are surfaces that have not yet been mapped. The southern portions were mapped by Voyager 2 in 1986
Credit NASA/JPL-Caltech

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RE: Uranus
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An international team of astronomers led by Apostolos Christou at Armagh Observatory has made the first ever observation of one of the satellites of the planet Uranus passing in front of another. The observation was made on the night of 4th May by Marton Hidas and Tim Brown, of the Las Cumbres Observatory Global Telescope, Santa Barbara, California, using the robotic Faulkes Telescope South at Siding Spring Observatory, Australia. This work involves a collaboration between scientists at Siding Spring, Las Cumbres, Armagh and Cardiff University.

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Uranus edge-on Rings
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The solar system is a playground for geometricians. Slicing up the solar system are myriad planes containing the orbits of every body that circles the Sun. All of these planes intersect at the Sun, but other than that they're not constrained, and no two bodies have perfectly matching orbital planes. However, because of the way that the solar system first formed from a spinning disk of material, most of the planets' orbital planes are quite close to each other, which is why the planets appear to travel across a single arc of the sky, the ecliptic.
Right now we are looking at Uranus' southern hemisphere, and the Sun is also lighting the southern hemisphere (and the south side of Uranus' rings). With Uranus very close to its equinox, our slightly tilted orbit will take us across the ring plane to the north -- and the shadowed side of the rings -- on May 2.
In a few months, with Uranus getting even closer to its equinox, our orbit will carry us back across to the south and sunlit side of the rings, on August 16. Then the equinox will happen on December 7, and the Sun will come to Uranus' north; we'll see the rings lit edge-on and then go in to darkness. Finally, on February 20, Earth will cross back to the north, and as Uranus' seasons advance we'll stay on the north side, seeing sunlit rings, until the next set of ring plane crossings comes with the 2049 equinox.

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Uranian irregular satellites
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Title: Light curves and colours of the faint Uranian irregular satellites Sycorax, Prospero, Stephano, Setebos and Trinculo
Authors: Michele Maris, Giovanni Carraro, M. Gabriela Parisi

After the work of Gladman et al. (1998), it is now assessed that many irregular satellites are orbiting around Uranus. Despite many studies have been performed in past years, very few is know for the light-curves of these objects and inconsistencies are present between colours derived by different authors. This situation motivated our effort to improve both the knowledge of colours and light curves. We present and discuss time series observations of Sycorax, Prospero, Stephano, Setebos and Trinculo, five faint irregular satellites of Uranus, carried out at VLT, ESO Paranal (Chile) in the nights between 29 and 30 July, 2005 and 25 and 30 November, 2005. We derive light curves for Sycorax and Prospero and colours for all of these these bodies. For Sycorax we obtain colours B-V =0.839 0.014, V-R = 0.531 0.005 and a light curve which is suggestive of a periodical variation with period about 3.6 hours and amplitude about 0.067 0.004 mag. The periods and colours we derive for Sycorax are in agreement with our previous determination in 1999 using NTT. We derive also a light-curve for Prospero which suggests an amplitude of about 0.2 mag and a periodicity of about 4 hours. However, the sparseness of our data, prevents a more precise characterisation of the light-curves, and we can not determine whether they are one-peaked or two-peaked. Hence, these periods and amplitudes have to be considered preliminary estimates. As for Setebos, Stephano and Trinculo the present data do not allow to derive any unambiguous periodicity, despite Setebos displays a significant variability with amplitude about as large as that of Prospero. Colours for Prospero, Setebos, Stephano and Trinculo are in marginal agreement with the literature.


Sycorax
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Light curves in R for Sycorax.
Data are for the nights of 2005, July 29th (left) and 30th (right). Squares in gray represents measurements of magnitudes for a common field star of similar magnitude. To avoid confusion error bars for the field star are not reported and the averaged magnitude is shifted.

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Uranus rings
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The rings around the planet Uranus may have been spotted 180 years before the accepted date for their discovery, according to a theory.

"February 22, 1789: A ring was suspected".

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