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A Touch of Blues

by Perry Pezzolanella

Saturn is clearly stealing the show this summer with its widened rings and Jupiter will command the coming autumn and winter nights, but two other worlds further away are frequently neglected and deserve at least a passing glance. Uranus and Neptune are often thought to be too dim and small to seriously observe, but both are actually quite easy with a little determination. Under clear, moonless skies away from city lights, it will be much less stressful to find Uranus and Neptune with the help of the finder charts that accompany this article.

Uranus (magnitude +5.7) and Neptune (magnitude +7.8) are dim because they orbit the Sun at a distance of 1.8 and 2.7 billion miles, respectively. In the depths of the outer Solar System, daytime sunlight is no brighter than a clear evening sky 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 slightly more methane (3%). These colors are dramatic whenever they are near stars of contrasting colors.

Uranus spends 2011 in Pisces to the left of the Circlet while Neptune is in Aquarius near the border of Capricornus, not far from where it was discovered in 1846. Neptune will be at opposition on August 22 while Uranus will be at opposition on September 25. 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 2012.

Given a night of steady seeing, a small telescope should be capable of resolving the discs and revealing the colors of these remote worlds; however, both planets are too far away to observe cloud detail or moons unless the telescope has an aperture of at least 16 inches. Uranus is 3.7 arcseconds across and Neptune is 2.4 arcseconds across. The planets appear distinctly different with Uranus having a rich turquoise hue while Neptune is a chilly, icy-blue.

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 both Uranus and Neptune. Amateur astrophotographers have been able to photograph a bright polar hood on Uranus and are beginning to coax out faint detail on Neptune. 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 can be a challenge to find, but patience will be rewarded with two planets that have colors different from all others. The touch of blue of both worlds is a fascinating sight to see, especially when near stars of other colors. They are definitely worth the challenge.