The Sky Tonight Update: Uranus at Opposition
This October 23rd, the blue-green planet will be at its closest approach to Earth and its face will be fully illuminated by the Sun. It will be brighter than any other time of the year and will be visible all night long. This is the best time to view Uranus. Due to its distance, it will only appear as a tiny blue-green dot in all but the most powerful telescopes.
At around the same time that Uranus passes opposition, it also makes its closest approach to the Earth – termed its perigee – making it appear at its brightest and largest.
This happens because when Uranus lies opposite the Sun in the sky, the solar system is lined up so that Uranus, the Earth and the Sun form a straight line with the Earth in the middle, on the same side of the Sun as Uranus.
In practice, however, Uranus orbits much further out in the solar system than the Earth – at an average distance from the Sun of 19.29 times that of the Earth, and so its angular size does not vary much as it cycles between opposition and solar conjunction.