Two papers on amateur observations of Uranus & Neptune

2021 October 1

Mike Foulkes

This edition of the Journal includes two papers describing Section observations of the ice giants in our solar system, Uranus and Neptune.

One paper, by the Section’s Uranus Coordinator, Kevin Bailey, describes observations of the planet made during the 2015 opposition. The second paper, by the Neptune Coordinator, Dr John Sussenbach, describes observations of Neptune made during the 2014 and 2015 apparitions.

The observation of any detail, if present, on the discs of either of these planets is made difficult due to their small angular diameters. For visual observers, care must be taken since any observed features may be illusory. Images must not be over-processed as this can introduce artefacts.

Since the mid-19th century, visual observations by both amateurs and professionals have sometimes revealed banding on the disc of Uranus, depending on axial inclination. The bands may have seemed controversial when Voyager 2 revealed little atmospheric detail during its fly-by. However, subsequent observations by the Hubble Space Telescope and large Earth-based instruments have shown that this appearance may have been seasonal, with the planet at other times showing banding and other atmospheric features. Little detail was detected on Neptune until Voyager 2 and subsequent observations, which revealed that the planet exhibited Great Dark Spots and large bright clouds.

Although little or no banding was initially recorded in digital images, the arrival of improved imaging cameras over recent years has now allowed it to be faintly recorded using larger amateur telescopes, especially in longer/near-IR wavelengths. Brighter spots have also been recorded on Neptune.

The Uranus paper (p.283) shows that banding was recorded by amateurs during 2015 both visually and in images, with some general agreement. Some latitude measurements are given, although the errors in these are recognised.

The Neptune paper (p.287) describes observations of a few bright spots. One such spot, designated Spot A, was followed in 2015. Although there is some scatter in the longitude data, the derived longitude drift is in very good agreement with professional measurements.

More recent observations of Uranus have shown much of the northern hemisphere, from the pole southwards, to appear bright. Lately, Neptune observations have generally shown no detail. However, on 2021 Aug 8, Darryl Milika and Pat Nicholas reported some bright clouds.

Uranus and Neptune are challenging, but these papers highlight what may be accomplished by amateurs with suitable equipment and careful observation. It is hoped that a greater number of observations can be made in the future, as this would help in the confirmation and tracking of any features observed.

Both planets are well placed for observation this autumn and in early winter. Neptune was at opposition on Sep 14 and Uranus will be at opposition on Nov 4. Moreover, Sep 23 marked the 175th anniversary of the discovery of Neptune by Johann Galle, who was assisted by Heinrich d’Arrest at the Berlin Observatory.

Any observations of either of these planets will be welcomed by the Section.

Mike Foulkes, Director of the Saturn, Uranus & Neptune Section