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Great galaxy of Andromeda

Be a Stargazer
(It's easy)

Today's planet hunters use Doppler spectroscopy and billion dollar telescopes to detect distant worlds. But all you need to be a stargazer are your naked eyes. On a clear night, looking skyward from a dark location, you can spot Venus and Jupiter, see the streak of our Milky Way, and even glimpse another galaxy two-million light years from the Earth.

Less Than Hubble-Vision

Hubble telescope being launched from shuttleWhile the view may be breathtaking, it's a tiny fraction of the universe. Naked-eye sky watchers, even under the best conditions, can count only about 3,000 of the billions and billions of stars in the cosmos.

Our vision is limited by the amount of light that can pass through the human eye. The pupil of an eye acts like the aperture of a camera. In the dark of night the pupil opens to about 8 mm in diameter. By contrast, the front lens of a common binocular used by amateur astronomers is about 50 mm in diameter. Binoculars and telescopes help stargazers by increasing the amount of light that is funneled to the eye—allowing perception of fainter objects.

Jupiter's Red SpotThese optical aids also magnify celestial objects—giving sky watchers a clear view of the craters on the moon and the red spot of Jupiter. But magnification is less critical than light collection for simple stargazing. And binoculars and telescopes with powerful magnification require mounts to hold images steady.

With a small telescope, and a stable mount, you can discover the rings of Saturn and the moons of Jupiter. With the most advanced telescopes, like Hubble, astronomers can look billions of light years into space and glimpse the birth of the universe.

Stargazing Tips

Get Where It's Dark

Philadelphia night skyline

The glow of city lights brightens the sky and obscures our view. City smog also dims starlight. So, the best stargazing spots are far from a crowd.

Just Look Up

When you gaze straight up toward the zenith, you are looking through about five miles of Earth's atmosphere. Toward the horizon, you look through many tens of miles of atmosphere—through turbulent gases that filter light and cause stars to twinkle. This difference in atmospheric depth is why the midday sun, high in the sky, appears much brighter than at sunset. (The setting sun is also red because the atmosphere reduces blue light more than red light.)

Sensitize Your Eyes

When you step from a bright room to the dark outdoors, your pupils widen immediately. But cells in the retina may take 15 minutes to a half an hour to become dark adapted. Be patient, and try not to look at any bright white lights. Red light does not affect this adaptation. (Think of the red taillights of a car.) So, if you need a flashlight, try using a red bulb or cellophane filter.

Know What to Find

Remember that the night sky is constantly changing! What you see depends on your location on earth, the time of day or night, and the time of year. Star maps and other guides can tell you what to expect from your vantage point.
Further ideas on amateur astronomy

Photos (1), (3) copyright © NASA; (2) copyright © STScI/NASA; (4) copyright © Vickie M. Feldman

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