Neptune, the eighth planet from the Sun and the Solar System's most distant reaches opposition on August 27, 2013. On this date it will be 28.9729 AU (approx. 4334.3 million km or 2693.2 million miles) from Earth and visible all night; rising above the eastern horizon at sunset and then setting in the west as the Sun again rises in the east. With an apparent magnitude of +7.8, it will also be at its brightest for the year.
Even when at it's brightest Neptune is not visible to the naked eye. It's the only planet that requires optical aid to be seen, although Uranus requires dark skies to be glimpsed. However, provided you know exactly where to look, Neptune is a relatively easy binocular and small telescope target.
Locating Neptune
Aquarius is a faint zodiac constellation with its brightest stars being of only 3rd magnitude. Neptune is currently moving retrograde and positioned almost exactly bang in the middle of the constellation, about 1 degree to the west of star Sigma Aquarii (σ Aqr - mag. +4.8). Located about 30 degrees NE of Neptune is the "Square of Pegasus" and about 20 degrees SE of Neptune is the brightest star in the surrounding region; Fomalhaut (α Psc) at magnitude +1.2.
The finder chart below shows the position of Neptune amongst the stars of Aquarius on August 27, 2013. Since its distant, it moves relatively little with respect to the background stars, hence the chart is not only valid at opposition but for many days later.
Neptune is currently better situated for observation from the tropics or southern hemisphere, where it appears higher in the sky, compared to northern latitudes.
Neptune Opposition Finder Chart - August 27, 2013 - pdf format
Neptune Opposition Data Table
| Date | August 27, 2013 |
|---|---|
| Right Ascension | 22hr 23m 41.9s |
| Declination | -10d 45m 56.5s |
| Apparent Magnitude | +7.8 |
| Apparent Size | 2.4" |
| Illumination (%) | 100.0 |
| Distance from Earth (AU) | 28.9729 |
| Constellation | Aquarius |