Locating Uranus

Fig. 1 The sky looking south at true midnight August 31 2008. The circle indicates the position of Uranus. Click for enlargement.

Fig. 2 The movement of Uranus from 31 August to 30 October 2008. Stars to visual magnitude 10 are shown. The diameter of the field is 5 arc degrees. Click for enlargement.

Uranus is the third largest of the so-called giant planets in the Solar system.

With an equatorial diameter (all giant planets demonstrate significant oblateness due to their fast rational periods) of 51,118 km Uranus is a little larger than Neptune. (The Earth has an equatorial diameter of 12,756 km.)

At favourable oppositions Uranus is well within reach of naked eye observation. For example, on March 14 in 2051 the planet will be at a distance of 17.2900 AU from Earth and its apparent visual magnitude will be 5.3.

Opposition in 2008 occurs on September 13 with Uranus at visual magnitude 5.7. From Orkney close to midnight Uranus will have a meridional altitude of 26.5 degrees. A good clear night free from light pollution will be necessary to see the planet without optical aid, a fete almost impossible to achieve in our heavily polluted skies.

However, a small binocular will readily show the planet. Those interested in taking up the challenge should start their searches in late August when twilight begins to fall off. Fig. 1 gives a general location chart for August 31. The circle encloses Uranus and represents a field of 5 arc degrees about average for a 8x30 binocular. Use the Square of Pegasus to locate the general area for Uranus and then refer to Fig. 2 for greater detail.

From Fig. 2 it will be seen that Uranus retrogrades towards the star 96 Aquari (mag. 5.58) being around 16 arc minutes from that star on October 31. Uranus will appear to move at the rate of a little under 2 arc minutes in 24 hours. This motion will enable observers to confirm the location of Uranus on a given night.

Uranus will have an apparent diameter of 3.66 arc seconds. Compare this to Mercury’s apparent diameter of a little over 5 arc seconds close to inferior conjunction.

(Note if you are lucky you may glimpse the first magnitude star Fomalhaut low on the southern horizon.)

JV 18/08/08