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  • Discovery of the Rings of Uranus

    Reggie Jones
    Today (March 10) is the 47th anniversary of the discovery of the rings of Uranus. On 10 March 1977, astronomers flying in the Kuiper Airborne Observatory (the ancestor of SOFIA) were set to observe Uranus, as it occulted the star SAO 158687, with the intention of studying the atmosphere of Uranus, via the star light shining through the atmosphere, as the planet moved in front of the star.
    Analysis of the data showed that the star had dipped in brightness 5 times before & after the occultation, corresponding to 5 narrow rings around the planet. We now know of 13 rings.
    Frederick William Herschel [1738-1822] recorded that he might have seen a ring, "inclined towards the red", in his notebook entry for 22 February 1789. Most modern astronomers doubt that Herschel could have seen the exceptionally dark rings, and no astronomer after Herschel claimed to see them, so far as I know. So his early "discovery" of the rings remains dubious, I think.
    SAO 158687 (HD 128598, HIP 71567) is a spectral class K1 sub giant or main sequence star, about 5800 light years away (Gaia DR2 parallax 0.5568 milli-arcseconds), with a Johnson V magnitude 8.76, J2000 ICRS coordinates RA 14:38:11.77888 DEC -14:57:17.1678.
    The picture is a Voyager 2 image of the rings of Uranus (see bottom link below). The NASA caption reads: “Voyager 2 image of Uranus' rings taken while the spacecraft was in the shadow of Uranus, about 3.5 hours after closest approach. The wide-angle exposure took 96 seconds, causing the short streaks which are background stars. The rings are made up of micrometer size particles and are very dark. The frame is about 10,000 km across.”
    The image is in forward scattered light, meaning that the sun is behind the rings. As a result, many new ring features were discovered in this image. It shows that the Uranian ring system is more complex than previously thought. This is the original NASA image. A cleaned up version is found on the Rings of Uranus Wikipedia page (see link below).
    https://en.wikipedia.org/wiki/Rings_of_Uranus (Rings of Uranus - Wikipedia)
    http://simbad.cfa.harvard.edu/simbad/sim-id... (SIMBAD entry for HD 128598)
    Reposted from Tim Thompson, NASA JPL Senior Astronomer (Retired).


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