WILLIAM DIFFIN'S URANIAN WEBPAGE


'A slight sound at evening lifts me up by the ears, and makes life seem inexpressibly serene and grand. It may be Uranus, or it may be in the shutter.'

Henry David Thoreau, 1841


Some observations of the planet Uranus, discovered relatively recently in 1781, and named after the Ancient Greek god of the heavens. Uranus, meaning 'heavenly' in Greek, was the personification of the sky, and the first ruler of the Universe. According to myth he was overthrown and castrated by his son Cronus, who himself was identified with the Roman god Saturn.

Uranus is at the limit of my equipment's ability to observe detail upon objects, not that there is much detail to see on Uranus, even with a huge professional telescope. At a mean distance of roughly 1,800,000,000 miles, Uranus is twice as far from the Sun as Saturn, and never exceeds 3.7 seconds of arc in apparent diameter. Uranus is really very far out, and out there space must start to look very forbidding and lonely.


Observation #199, 2011.I.9

1718 UT
Taking advantage of a recent conjunction of Jupiter and Uranus, in the one hour of clear sky in weeks I managed to capture this my first tiny image of the planet Uranus. It's a start.

Uranus 2011.I.9.1718
URANUS
2011.I.9.1718 UT

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Observation #124, 2009.VIII.25

0157 UT
A long star-hop from Phi Aquarii taking in 96 Aquarii and a string of Hipparcos catalogue stars along the way to find Uranus. Seeing must have stilled and collimation must have been good; even at 40 magnification it was clear that Uranus is a dot and not a point. The green hue of the planet was plainly evident, whilst at 400 magnification the tiny disc of the planet was visible in clear moments.

0210
In a clear moment I finally saw limb darkening around the edge of the Uranian disc, and then again every time the seeing stilled. The disc appeared to fall into shadow around its edge, appearing very much like a ball and not merely a featureless greenish disc. The limb-darkening effect is due to the absorption of light by the methane atmosphere, which is more obvious at the periphery of the disc, where the line of sight is through a greater thickness of Uranus' light-absorbing atmosphere, than at the centre of the disc.

Uranus 2009.VIII.25.0210
URANUS
2009.VIII.25.0210 UT

0221
Tried 600 magnification, but this was no good, entirely beyond the light-grasp of my telescope. With cloud moving in I ended observations.

My skills as an observer are still improving. Tonight I learned or reminded myself that the biggest mistake an astronomer can make is to expect to see all of the detail in an object at once. It takes some long hard peering and use of observational techniques to fully apprehend all of the available detail in an image, especially the techniques of averted vision, of tweaking the focus, and of trying different magnifications in order to find the optimum. My successful observation of Uranus was only due to hard squinting at a fat four-pointed greenish star, swimming in and out of focus at the centre of a wide halo etched with concentric circles. Only by peering into the very centre of this 'star' could the disc of Uranus be made out in still moments.

Outer Solar System 2009.VIII.25

This is a diagram showing the positions of Uranus relative to the Earth on the date of this observation. Earth is on the same side of the Sun as Uranus, approaching opposition (when the Sun, Earth, and Uranus are directly in line).

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Observation #30, 2007.XII.10

1923 UT
Collimation of telescope incomplete, but had an opportunity to observe Uranus in any case. Medium seeing, Antoniadi III. At 40 magnification stars were clear and plainly visible down to ninth magnitude in spite of light pollution. Found the planet by star-hopping from the triangle of Phi3 and Phi2 Aquarii with HIP114855 again, but upon increasing magnitude the image became increasingly difficult to focus upon. At 400 magnification (absolutely necessary to use such a high magnification on this world) the image was impossible to focus upon directly (as were stars) but was considerably clearer than the image obtained during my prior observation. Image at 400 magnification was of an out-of-focus grey-greenish star. Possibly, if perfectly resolved at this magnification, Uranus might appear as a dot rather than a star, and it may be possible to observe limb-darkening around its edges. This is not entirely impossible; my computer calculates that this world subtends 3" of arc at present and will subtend 1/5" more than that at opposition in September next year (cf. recent observation of Mars at 15" of arc).


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