Mohawk Valley Astronomical Society

Return to Newsletter Index

City Blues

by Perry Pezzolanella

Not much consideration is given when it comes to observing Uranus and Neptune and that is sad because both worlds are actually quite easy to find and capable of revealing detail given the proper equipment. Under clear, moonless skies in the dark countryside, 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 (3%) in Neptune’s atmosphere absorbs the red component of sunlight and scatters the blue creating a beautiful blue planet. Uranus does not appear as blue because it has a little less methane (2%) and unlike Neptune it has a ruddy haze, which shifts its color towards the green giving it a turquoise hue. These colors are dramatic whenever they are near stars of contrasting colors.

Uranus spends 2016 in Pisces to the left of the Great Square of Pegasus near the bright star Zeta Piscum while Neptune is in Aquarius close to the bright star Lambda Aquarii. Neptune will be at opposition on September 2 while Uranus will be at opposition on October 15. 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 and into early 2017 with Neptune fading into the evening twilight by February and Uranus by March.

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 Barton-Brown Observatory (BBO) at the Waterville Public Library houses a research grade, 16-inch Schmidt-Cassegrain telescope with superior optics. In the relatively dark skies south of Utica’s bright city lights it reveals Uranus as a true turquoise globe and most of the time two of the five largest moons, Oberon and Titania, are visible. The other three moons of Uranus: Umbriel, Ariel, and Miranda, are dimmer and have yet to be seen; all five moons shine at magnitude +14 to +15. Neptune is a chilly-bluish, tiny globe with Triton shining nearby most of the time, but quite dim at magnitude +13.5.

Serious attention should be given to Uranus as it has become a very stormy planet these past several years. Large white spots have been observed erupting, growing, and then elongating and dissipating. The advancement in technology and photography is making amateur photos equaling and even exceeding the quality of what could be done with the giant, professional telescopes decades ago. Neptune has been changeable with dusky patches and dark and bright spots appearing and disappearing. A magnification of at least 500x for Uranus and 900x for Neptune are highly recommended in order to have a chance at photographing any detail and using a yellow-green (Wratten #11) filter will improve the odds.

Finding Uranus and Neptune and observing their unusual colors is worth the effort. Traveling to the BBO well south and away from the bright lights of Utica will make the effort easier, but Uranus and Neptune will still reveal their soft bluish glow even in brighter city skies.