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Understanding orbits | Brightness | Viewing tips
Of course, you have to know what's up there. After studying this page, visit our Explore Tonight's Sky page. If you're considering purchasing a telescope, see our page that explains how telescopes work and what to look for. Understanding OrbitsSome of the brightest and most interesting objects in the night sky are the planets in our solar system. But planets aren't always visible. Each planet rotates at a different pace. We see a planet because it reflects the Sun's light. So when a planet is behind the Sun, or in its glare, we can't see it. (See Why Planets Orbit.) Outer
planets Inner
planets See Explore Tonight's Sky to find out what's visible now. Apparent BrightnessThe brightness of stars and other celestial objects is measured on a scale of apparent brightness. Smaller numbers are brighter (negative numbers are the brightest). The scale assumes dark skies.
Viewing tipsWhether you view the night sky with your naked eye, binoculars, or a telescope, here are a few tips to make your experience more worthwhile. Obviously, a dark location is helpful. But no matter how much light surrounds you, more is always worse. Turn off any lights you can. Also, allow a few minutes for your eyes to adapt to the darkness. And use a red-filtered flashlight to read your star charts (you can make one with red cellophane). One thing you can't control is the atmosphere. Even a cloud-free night isn't always great for viewing. When you look directly overhead, you're peering through about 7 miles of the troposphere, the densest portion of Earth's atmosphere; the light from an object nearer the horizon filters through dozens of miles of the troposphere. (See more on Earth's atmosphere.) The atmosphere affects viewing in two ways: First, turbulent air makes objects appear to jump around or twinkle. Second, gases in the atmosphere filter light differently on different nights, making objects appear more or less red. Clear nights are said to have higher transparency. Only experience will tell you which nights are good for viewing. ez Explore Tonight's Sky:
learn what's visible now Related pages on the
Web Photograph:
NASA/NSSDC |
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A
good pair of binoculars is all you need to explore the night sky,
and even the old naked eye can perform pretty well. Of course, the
best viewing is always under the darkest skies. But even in a city,
with a decent amateur telescope, you can see 
Visible with naked eye
Binoculars needed
Telescope needed
Large telescope needed
