Observe remote Uranus at this favourable opposition

Uranus, the remote seventh planet from the Sun and the third-largest planet overall, comes to opposition on the night of 4/5 November, when it can be easily found through a pair of humble 10 x 50 binoculars and observed all night through a small telescope.

An infrared composite image of the two hemispheres of Uranus obtained with the Keck Telescope’s adaptive optics. Image: Lawrence Sromovsky, University of Wisconsin–Madison/W.W. Keck Observatory.

Although Uranus doesn’t offer Jupiter-like observing pyrotechnics to compare with those which will be enjoyed over Bonfire Night on the following evening, for observers based at mid-northern latitudes, which includes the UK, the planet is very well placed around midnight, lying halfway up the southern sky among the stars of Aries. At this opposition Uranus lies 15°10′ north of the celestial equator, giving it an altitude of between 49 to 54 degrees when it culminates due south.

These are heady observing circumstances for the aforementioned northern observers. For the last time that Uranus lay this high in the sky across the UK one has to go way back to the planet’s opposition of 8 February 1960, the year John F Kennedy was elected president of the United States of America and the Beatles first performed as such, in Hamburg, Germany. Uranus was located then in Leo and over the course of the past 61 years the planet sank to a nadir (low-point) for the UK at its opposition on 24 June 1989 (declination 23° 40’ south) in Sagittarius and has been steadily heading north since.

Uranus was discovered on 13 March 1781 and its orbital period of just over 84 years means it’s made only two complete trips around the Sun since it was found by William Herschel.

Uranus’ vast distance of 2.8 billion kilometres (18.74 astronomical units), more than twice as far as Saturn and between four and five times Jupiter’s distance, means sunlight reflected from the ice-giant planet takes around 2.7 hours to reach Earth. Despite these seemingly dismaying numbers, Uranus shines just about bright enough, at magnitude +5.7, to be seen with the naked eye by keen-eyed individuals looking for it under the best observing conditions. Furthermore, just a small telescope operating at high magnification is all that’s required to show Uranus’ tiny (3.7”) yet perceptible blue-green disc.

Uranus is a giant planet, largely made up of an ‘icy fluid’ of water, methane and ammonia surrounding a small rocky core. Astronomer’s term it, along with Neptune, as an ice giant planet. What we see through a telescope are the tops of layers of clouds of methane high in its atmosphere. It’s a challenge to see detail in these cloud tops, as, unlike Jupiter and even Saturn, the view is largely bland apart from subtle equatorial belts, or bands, that can be seen to best effect through telescopic apertures in excess of 250mm (10 inches) or so.

Uranus’ north pole is be tilted towards us at this year’s opposition.

Experienced planetary observers, such as David Gray and Paul Abel, are producing fantastic drawings of Uranus showing the brighter polar region and those dusky belts. Also present-day digital images of the planet are often streets ahead of what was being produced just a decade or so ago. Bizarrely, Uranus rotates on its side rather than ‘vertically’, as do the other planets. Uranus’ rotational axis is tilted by almost 98 degrees to the ecliptic! In 2008, the planet’s equatorial regions were advantageously seen, presenting ‘edge-on’ to us. Since however, Uranus’ north pole has been steadily coming into view, making it increasingly difficult to view the planet’s subtle banding.

A drawing of Uranus through a 415mm (16.3-inch) Dall–Kirkham telescope on 3 August 2021. Equatorial banding is faint but clear to see towards the left edge of Uranus’ disc. North is up. Sketch: David Gray.

Uranus sports a large family of moons, 27 at the last count. Four or maybe five of those are within range visually of amateur-sized telescopes (at least a 250–300mm [ten- to twelve-inch] aperture is recommended); Oberon and Titania (magnitude +13.9 and +13.7, respectively), are the outermost satellites and the easiest to spot as they can venture as far as 40 and 30 arcseconds from Uranus. Umbriel and Ariel (magnitude +14.8 and +14.2, respectively) orbit closer in and are affected more by Uranus’ glare. They can be imaged, though.

Uranus imaged on 24 September 2021 through a Celestron 14 SCT. Image: Luigi Morrone.

So far during 2021, Uranus has been located among the stars of Aries and this is where you can find it now. On opposition night, Thursday night into Friday morning (4/5 November), it is located around halfway between 36 and 31 Arietis, sixth-magnitude stars that are three degrees or so north-west and south-east of Uranus, respectively. From London, Uranus rises at around sunset and climbs to an altitude of 54 degrees or so at about 11.40pm GMT. In Edinburgh, the planet peaks at around 50 degrees at about midnight. Uranus can be observed while lying above 20 degrees elevation from about 7pm to 4.30am.

Uranus lies among the stars of southern Aries throughout November. Sweep for it around halfway between the sixth-magnitude stars 36 and 31 Arietis. AN graphics by Greg Smye-Rumsby.

With Uranus now showing as well from UK shores, there’s never been a better time to bring to bear the rich arsenal of modern astronomical technology, primarily colour (green or yellow-green) and narrowband filters, superb optics and high frame rate cameras. Let’s hope for a fair number of clear nights across the rest of the year so Uranus can get the coverage its lofty location deserves.