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Uranus at opposition

Posted: 3 October 2013

Uranus, the seventh planet from the Sun and the third largest, comes to opposition on 3 October among the stars of Pisces.

Locate Uranus on the border between Pisces and Cetus, five degrees south of delta Piscium. AN graphic by Greg Smye-Rumsby
Uranus has an equatorial diameter of 51,118km, which is just larger than its more remote fellow ice giant Neptune (50,538km). But it's significantly less massive than Neptune. Its opposition magnitude is +5.7, so theoretically it's visible to the naked eye but, it will require a dark site and a very transparent sky for a successful detection.

Its precise position is RA 00h 39m 56.8s, DEC +03o 30' 28.9", midway between the naked eye stars SAO 109916 (mag. +5.7) and 44 Piscium (mag. +5.8). Thankfully it's an easy object in binoculars; If you're unable to find Uranus with the unaided eye, binoculars will do. Trace a line between the bottom two stars in the Circlet - kappa (k) Piscium (magnitude +4.9) and lambda (l) Piscium (magnitude +4.5) - and move east along this imaginary line by some 14 degrees, which amounts to just two actual fields-of-view of 10 x 50 binoculars. If Uranus is centered in the field of 10 x 50 binoculars, both 96 and 44 Piscium will just about be included in the same field.

The view is transformed in a telescope with magnification of x30 and above into a shimmering blue-green disc 3.7 arcseconds across. Astronomy Now's Peter Grego reports: "The planet's cloud features are extremely subtle, and good conditions, a sizeable telescope and a keen eye are necessary to glimpse a trace of this detail. Uranus currently displays a dusky south polar region, a brighter zone bordering it in the north temperate region, a broad dusky north equatorial band and another bright zone just south of the equator."

An astronomical sketh of Uranus made by Peter Grego on 26 August 2013 through a 200mm Schmidt-Cassegrain telescope. Note the subtle banding.
Uranus' more advantaged place in UK skies makes it more than a viable imaging target. Get a copy of Astronomy Now's October issue (available for iPad and iPhone) to find out all you need to know in our special imaging Uranus article written by world-renowned and trail-blazing astrophotographer Damian Peach. Uranus has an orbital period of 84 years and an extraordinary axial tilt of 97.86 degrees, which means it effectively rotates on it side! It has a higher orbital eccentricity than Neptune at 0.047, with an average distance from the Sun of 2.87 billion kilometers (19.2 AU). At this opposition, the planet lies 2.85 billion kilometres (19.04 AU) distant.

Uranus has five moons of 16th mag. and brighter and the two brightest, Titania (+13.9) and Oberon (+14.1) can be seen in apertures around 250-300mm under good conditions. Ariel (+14.2) and Umbriel (+14.8) can be easily imaged.

Uranus imaged by Damian Peach on August 21, 2013, with a Celestron 14, an ASI120MM camera with RG610 filter. Hamble, UK.

Uranus' visibility from the UK

The ice giant has become much more forgiving in the last few years, and at this opposition it lies just north of the celestial equator and gets over 40 degrees above the southern horizon at its best. Uranus is available for observation around 9pm BST and transits due south at 1am. It can be followed for most of the night until dipping below 20 degrees altitude at 5am.

From the USA

Uranus is superbly placed across the USA with it being at a decent altitude for over eight hours on opposition night. From latitudes of New York (and Chicago), Uranus is up from 8.15pm (EDT local New York time), culminates at 12.40am at 52 degrees up and it's not until 5am that Uranus' altitude becomes a problem. From further south, the ice giant culminates at over 60 degrees and has a slightly longer observing period. Imagers have a great chance to secure some good frames to try for that first or best-ever image; have a quick look at the Internet to see what can be achieved and get a copy of Astronomy Now for your iPad or iPhone (see above).

From Australia and New Zealand

Although not as well-placed as in the southern states of America, Uranus still warrants plenty of attention this month. The seventh planet can be observed from 7.30pm EST to 4am, with it being at its highest, a very satisfactory 50 degrees, just before midnight.

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