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Uranus will be well placed for observation, lying in the constellation Pisces, well above the horizon for much of the night. Regardless of your location, Uranus will reach its highest point in the sky at around midnight, local time, an optimal positioning that occurs when it makes its closest approach to the point in the sky directly opposite to the Sun – an event termed opposition, the exact moment of which will be 06:58 PDT. Since the Sun reaches its greatest distance below the horizon at midnight, the point opposite to it is highest in the sky at the same time.
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 in the night sky. This happens because when Uranus lies opposite to the Sun in the night sky, the Solar System is lined up so that Uranus, the Earth and the Sun lie in 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 AU as compared to the Earth's average distance of 1 AU – and so its angular size does not vary much as it cycles between opposition and solar conjunction.
On this occasion, Uranus will lie at a distance of 19.04 AU, and its disk will measure 3.7 arcsec in diameter, shining at magnitude 5.7. Even at its closest approach to the Earth, however, it is not possible to distinguish it as more than a star-like point of light without the aid of a telescope. Over the weeks following its opposition, Uranus will reach its highest point in the sky four minutes earlier each night, gradually receding from the pre-dawn morning sky whilst remaining visible in the evening sky for a few months.
Date: Thursday, October 3, 2013
Time: 8 p.m. - 11:59 p.m. Pacific