At opposition this week and as bright as it will be for the next 190 years, it's time to find your way to Pluto, a frigid enigma at the edge of night.
Pluto may be a dwarf planet, but it can pose a gigantic challenge. Not only has the planet been fading since its 1989 perihelion, it's now playing hide-and-seek in star-rich Sagittarius at the pit of the ecliptic. Back when I first saw it in the early '80s, Pluto strode the star-barren fields of eastern Virgo at magnitude of +13.7.
These nights, it winks back weakly at magnitude +14.2. What used to be an easy catch for an 8-inch scope under dark skies will probably require a 10-inch now. Fortunately, telescope aperture sizes have increased and prices have dropped since the heyday of Madonna, keeping Pluto within the range of many observers.
I hope you'll be one of them. This is the perfect week to seek this icy dot, with the Moon departing the evening sky and darkness returning like a welcome breeze. Pluto reached opposition on July 10th just below the familiar Teaspoon asterism in eastern Sagittarius, so it's brighter now than at any other time this year. Make that brighter than it will be for the next 190 years.
Because of its orbital eccentricity, the dwarf planet's distance from the Sun varies from 29.6 a.u. at perihelion, which occurred in 1989, to 49.3 a.u., when it reaches aphelion in Cetus in February 2114. The great grandchildren of today's parents will need a 16-inch scope to spot the magnitude +16 dwarf planet in that distant year. Not till 2207 will Pluto be this bright again.
Pluto culminates around 1 a.m. local time at mid-month, but you can begin looking around 11 p.m. when the dwarf planet stands about 20° high in the southeastern sky from mid-northern latitudes.
First, locate the Teaspoon, then focus your attention on Pi (π) Sagittarii (magnitude +2.8), the star just east and above the bottom of the spoon. Center this star in your finderscope and slide just under 1° southeast to +6.4 magnitude HD 179201. Pluto is currently 1° east and slightly north of the star. On the night of the 12th, it's conveniently just 3′ due west of 8th-magnitude HD 180332.
You're now ready to use the deeper map to wade through a sea of 13th- and 14th-magnitude stars to Pluto. Be methodical and make use of patterns like all seasoned star-hoppers do. I like joining field stars into triangles, "batons," and diamonds to work my way to a faint target. Because Pluto moves slowly night to night, the mini-asterisms you've created will make returning to the field to check on its motion much easier.
While some might be perfectly confident that they've seen Pluto on the first try, it's much more satisfying to return the next clear night and look it up again. Not only will you confirm your first observation but seeing it move from night to night firms our connection to this remote place, like going on a "ride-along."
American astronomer Clyde Tombaugh used a related method to make his discovery of Pluto in 1930. He took pairs of photos on different nights and compared them in a blink comparator to determine if any objects had shifted their position. Little did he know that in 2006 his planet would be declared unfit for the job and reclassified as a dwarf planet.
This simulated flyover of two regions on Pluto, northwestern Sputnik Planum (Sputnik Plain) and Hillary Montes (Hillary Mountains), was created from New Horizons close-approach images.
Whatever you choose to call it, Pluto can speak for itself. Only 1,475 miles across or two-thirds the size of the Moon, its incredibly diverse landscapes include flowing nitrogen ice warmed by residual heat from its core, a now-frozen liquid nitrogen lake, glaciers, and a multi-layered atmosphere dotted with ethane clouds. I don't care how cold it is, I want to go there! And there's only one way to do it — through my telescope.