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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
 While 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.
 These 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
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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