|Jupiter and Saturn may dominate the early summer evenings, but two other gas giants will enter the scene when Saturn exits and Jupiter grows lower in the sky. Uranus and Neptune are often overlooked because they are dim and considered too remote to seriously observe, but this year it will be easier than ever to locate Neptune, and Uranus will not be any more difficult to find than last year. Using the finder charts that accompany this article and clear, moonless nights away from city lights will make it surprisingly easy to find and track these nearly forgotten worlds.
Uranus and Neptune are dim because they orbit the Sun at a distance of 1.8 and 2.8 billion miles, respectively. In the dim depths of the outer Solar System the daytime Sun is no brighter than a clear evening on Earth shortly after sunset. Both planets are about four times larger than Earth, slightly over 30,000 miles in diameter, and have thick atmospheres that are completely cloudy. The small amount of methane (2%) in Uranus’ atmosphere absorbs the red component of sunlight and scatters the blue creating a turquoise hue. Neptune appears even bluer since it is not as hazy and has more methane (3%). These colors are dramatic whenever they are near stars of contrasting colors.
Uranus spends all of 2008 in Aquarius while Neptune is in Capricornus. Neptune is at opposition on August 15 at magnitude +7.8. Uranus is at opposition on September 13 at magnitude +5.7. Rising at sunset and setting at sunrise, both worlds will be up all night on these dates. They will remain in the evening sky for the rest of the year until they are lost in the evening twilight by February 2009. Uranus can be found to the east of the 3rd magnitude star Phi Aquarii, which is the same star it was to the west of last year. Neptune is beautifully placed just west of a string of a nearly vertical trio of 5th magnitude stars: 42, 44, and 45 Capricorni, just above the 3rd magnitude star Delta Capricorni.
A small telescope is capable of resolving the discs and revealing the colors of these remote worlds given a night of steady seeing. The planets appear distinctly different with Uranus having a rich turquoise hue while Neptune is a chilly icy-blue disc. Uranus is 3.7 arcseconds across and 1.78 billion miles away at it closest point this year. Neptune is 2.4 arcseconds across and 2.70 billion miles away. Both planets are too far away to observe cloud detail or moons unless the telescope is at least 16 inches.
The MVAS Apollo Observatory houses a research grade, 16-inch Schmidt-Cassegrain telescope and its superior optics in the relatively dark country sky has revealed Uranus as a true turquoise globe with two moons, Oberon and Titania, occasionally visible. The other three rather large moons of Uranus; Umbriel, Ariel, and Miranda are more difficult to see and all five moons shine at magnitude +14 to +15. Neptune appears like a tiny bluish globe with magnitude +13.5 Triton shining dimly nearby.
Observing detail on each planet is the biggest challenge, but white spots and dusky banding have been noted on Uranus. Neptune is always notorious for rapidly changing cloud belts and spots. Recent amateur photography has improved to the point where a bright polar hood has been photographed on Uranus and the fluctuations of Neptune’s brightness has been recorded. A magnification of at least 500x for Uranus and 900x for Neptune along with a yellow-green (Wratten #11) filter are required in order to have a chance at photographing any detail.
Uranus and Neptune may seem too remote and small to bother observing, much less photographing compared to Mars, Jupiter, and Saturn, but both worlds have the potential to surprise. Amateurs are coaxing detail out of their photographs of Mercury and Venus, so why not give Uranus and Neptune a try? These remote blue worlds in the starry heavens of a crystal clear night beckon for our cameras and eyes.