Naked-Eye Observing (Summer)

May 20, 2008

Darn it! You’re away on a trip and you’re without telescope or binoculars. And you find yourself under a perfect night sky. Here are a few tips to help you enjoy the sights, sans optiques.


The Basics

• In good dark sky, you can see 1,500 to 2,000 stars. Not to mention the star-clogged arms of the Milky Way. It’s a jaw-dropping sight, to be enjoyed whenever you can.

• Test your eyes by resolving the famed “double double” star, epsilon Lyrae. Located just NE of Vega, this double star is barely resolved into two components by a keen pair of eyes. Each component itself is a closely-spaced double star resolvable in a telescope… it’s a quadruple star.

• Find M13 in Hercules, magnitude 5.7. While just at the limit of human eyesight, M13 packs nearly a million stars that are 13 billion years old. While M13 lies a distant 25,000 light years from Earth, Kurt Vonnegut wrote, “Every passing hour brings the Solar System forty-three thousand miles closer to Globular Cluster M13 in Hercules — and still there are some misfits who insist that there is no such thing as progress.”

• Those of you in the southern hemisphere can inspect the Magellanic clouds, and try to spot the globular clusters 47 Tucanae and Omega Centauri.

A Deeper Look

• You can see dozens of artificial satellites whizzing by. They look like bright stars that decided to make a break for it. Follow the path of each, and note any change in brightness as it tumbles or moves into the Earth’s shadow. Also note the time. You might be able to determine which satellite you saw using the tools on websites like Heavens Above.

• If you’ve got very dark sky, see if you can spot the whitish zodiacal light extending along the ecliptic in the west after sunset or east before sunrise. It’s caused by sunlight scattering off dust particles in the plane of the solar system.

• Daytime tip: Poke a pinhole in a business card and project the image of the sun on a piece of paper (don’t look directly at the sun). You may see a few larger sunspots if you project the unmagnified image many feet away.

Good To Know

Just before the telescope was invented, one of the most important (and flamboyant) astronomers of all time, Tycho Brahe, made thousands of precise naked-eye observations of the stars and planets. His measurements enabled his assistant Kepler to discover the Laws of Planetary Motion.

Personal View

Epsilon Lyrae is a favorite test of visual acuity. Try as I might, my eyes can no longer resolve it, though I could split it easily well into my 20′s. Alas. Does any part of the human body improve with age?

Posted in Telescopes and Observing



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