Mohawk Valley Astronomical Society

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House of Blues

by Perry Pezzolanella

There are always interesting options when viewing the night sky after seeing the familiar celestial wonders including the commonly brighter planets, but two distant planets are frequently forgotten and should be considered targets when everything else has been seen many times before. 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 and south of city lights, it is possible 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 dim 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 2013 to the lower left of the Great Square of Pegasus while Neptune is in Aquarius below the Water Jar asterism. Neptune will be at opposition on August 26 while Uranus will be at opposition on October 3. 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 Neptune is lost in the evening twilight by February and Uranus by March 2014.

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 disc.

The MVAS Observatory at the Waterville Public Library houses a research grade, 16-inch Schmidt-Cassegrain telescope and its superior optics in the relatively dark skies south of city lights 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, but quite easy to identify.

Observing detail on each planet was once thought to be only possible with huge telescopes or sophisticated spacecraft. White spots and dusky banding have been noted on both Uranus and Neptune and amateur astrophotographers have been able to photograph these details. 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 their bluish colors will make them easy to identify and follow on clear nights. The MVAS Observatory at its new location on the southern edge of Waterville with nothing but dark rural skies for endless miles to the south will offer incredible views of these two remote worlds. The observatory is no longer a dome but looks like a small house with a large roll off roof. It will truly be our own “House of Blues” with the bluish light of Uranus and Neptune captivating our attention in the dark surroundings.