Two distant planets truly deserve attention but are consistently overlooked with Mars, Jupiter, and Saturn usually getting the most attention. 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 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 2015 in Pisces to the left of the Great Square of Pegasus while Neptune is in Aquarius below the Water Jar asterism. Neptune will be at opposition on September 1 while Uranus will be at opposition on October 11. 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 2016 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 and its superior optics in the relatively dark skies south of Utica’s bright city lights consistently reveal 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.
Capturing detail on both of these planets is getting easier thanks to advances in technology and photography; amateur photos are rivaling and even exceeding the quality of what could be done with the giant, professional telescopes decades ago. Uranus has been very active for over a decade with numerous white spots erupting, spreading, and dissipating along with dusky banding appearing. Neptune has also revealed dusky patches and banding in spite of its smaller size, and bright spots have also been photographed. 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; using a yellow-green (Wratten #11) filter will improve the odds.
Simply finding Uranus and Neptune and observing their unusual colors is worth it. The BBO in its location well south and away from the bright lights of Utica on the southern edge of Waterville is perfect for hunting and observing these remote worlds. Uranus and Neptune will easily reveal their soft bluish glow to the inquiring eyes during the peaceful village nights.