Sky Talk September 2011: Spotting Uranus

We’ve discussed all five of the bright naked-eye planets (Mercury, Venus, Mars, Jupiter, and Saturn) in this column frequently over the years but never the outer ones due to their remoteness and dimness. However, this month we go deep into the solar system to find Uranus. Seeing it for the first time is guaranteed to excite you—and bring with it a sense of great accomplishment as an observer.

Let’s begin with a few facts about Uranus itself. It was the first planet ever discovered (the other five having been known since antiquity) by the great astronomer Sir William Herschel with his homemade 6.2-inch reflecting telescope in 1781. (It turns out that Galileo actually saw Uranus much earlier with his primitive little refractor but failed to recognize it as such.) Lying some 1.8 billion miles from the Sun (twice as remote as Saturn), its visibility at such a great distance is partly due to its size—nearly four times the diameter of our Earth.

At its brightest, Uranus reaches visual magnitude +5.5 and can actually be glimpsed with the unaided eye under excellent dark-sky conditions. More typically, binoculars are needed to identify it. In a small telescope like the Scientific’s 60mm refractor, it looks obviously non-stellar in appearance at 35x and with the 87x eyepiece it shows a tiny but definite greenish disc. But the challenge is finding it! It’s currently located in the southeastern evening sky in the constellation Pisces—directly under the huge Great Square of Pegasus asterism. Begin by setting your Scientific’s Star and Planet Locator to, say, 9 p.m. on September 15th. Next, identify the Square itself (it’s actually more of a rectangle than a square!), which you’ll find marked “Great Square” on the star chart. Now follow a line from the top star to the bottom star on the left side of the Square precisely its own distance downward in the sky. You are now right on top of Uranus!

Examine the area first with binoculars, looking for a relatively obvious “star” that doesn’t quite look like other stars around it. Most observers find that the planet appears brighter than they actually had expected. And it doesn’t seem to twinkle like surrounding stars (see the June 2008, Sky Talk entitled “Stars Twinkle—Planets Don’t”). Finally, use your telescope’s low-power eyepiece to locate and center the suspected planet, and then switch to a higher magnification. If all goes well, you’ve just added another world to those you’ve always known, and in doing so doubled the size of the solar system you’ve previously explored!

For a detailed finder chart of Uranus (and Neptune as well, which lies nearby and is also visible in small scopes), go to www.skyandtelescope.com. In the search window type “Uranus in 2011” and you’ll be led to general finding charts and then more detailed ones in printable PDF formats for both planets.

—James Mullaney
Former assistant editor at Sky & Telescope magazine and author of eight books on stargazing.