Have you ever seen planet Uranus? If not, make the most of any clear UK skies in the early evening of Sunday, 10 February 2019 when this distant ‘ice giant’ lies closely in the same line of sight as relatively nearby Mars and our own Moon, both acting as convenient celestial pointers to their distant planetary sibling.
With a diameter four times that of the Earth, Uranus is the third largest planet in the solar system. It orbits the Sun once every 84 years at a mean distance of 2,875 million kilometres, or 19 times further away from the Sun than the Earth. Like its more distant sibling Neptune, Uranus is considered an ice giant because, while it is largely composed of hydrogen and helium gas like its larger kin Jupiter and Saturn, Uranus also contains methane gas plus water and ammonia in the form of ice.
On the UK evening of 10 February, Uranus lies just under two degrees (1° 51′, to be precise) to the east of the Red Planet. On this night Mars shines at magnitude +1.0 and sports a tiny gibbous disc just 5.8 arcseconds across owing to its distance of 241 million kilometres from Earth. Uranus is almost 7½ times the diameter of Mars, but lies 3,024 million kilometres from us on 10 February. The Moon – on our doorstep in comparison – is just 392,380 kilometres away this night. Put another way, Mars is in excess of 600 times farther away than the Moon, while Uranus is 12½ times farther away than Mars!
Mars passes a shade under one degree (58½ arcminutes, to be precise) north of Uranus around 05:40 UT on Wednesday, 13 February. Both planets are in the constellation of Aries at the time, the Red Planet being in excess of 80 times the brighter of the pair.