As summer ends and the nights turn longer and colder, observers should head out and look for the solar system’s two outermost major planets. Each planet reaches opposition (when the world lies on the opposite side of Earth from the Sun) within several weeks of each other this year. Uranus lies at this point in its orbit October 3, less than six weeks after its more distant sister planet, Neptune, which arrives at opposition August 26. Both will be easy to find and fascinating to observe these fall evenings, as opposition means a planet is at its closest to Earth for the year and therefore appears brightest in the night sky.



Neptune’s opposition only marks the middle of the planet’s prime observing season., however. In fact, the most distant planet lies so far from Earth (some 2.7 billion miles [4.3 billion kilometers]) that its appearance hardly changes during the next several months. It remains at its peak brightness — magnitude 7.8 — until mid-October and doesn’t fade below magnitude 7.9 until 2014. It also stands higher in the evening sky during autumn than in late summer.



You’ll need binoculars or a telescope to spot Neptune. It resides among the background stars of Aquarius, roughly midway between Sigma (σ) Aquarii (magnitude 4.8) and 38 Aqr (magnitude 5.4) throughout the summer and fall. These two stars lie 5° apart and will appear in the same binocular field. Turn a telescope on Neptune, and boost the magnification to see its tiny blue-gray disk.