2. Most people imagine that Mars must be a fascinating planet through a telescope. Reality check: Its tiny, blurry, nearly featureless disc creates more disappointment than any other celestial object. The best planets? Jupiter and Saturn.
3. Spring finds the Big Dipper highest, its two pointer stars at the left end of its bowl aiming down to Polaris, the North Star. Beginners imagine that the North Star is bright. But 45 other stars are brighter. Polaris' real claim to fame is that it is the only star that doesn't appear to move.
4. No other bright star travels through space in such a strange way as spring's brightest star: orange Arcturus. Instead of going around the galaxy's flat plane with all the other stars, it orbits perpendicularly up into the lonely darkness away from the disc. Then it dives back through the galactic plane 100 million years later. As a result, Arcturus is now meeting us for the first and only time. We are passing each other briefly, like ships in the night.
5. The busiest part of the night sky is, oddly enough, the darkest. Halfway up the southern spring sky is Virgo, marked by a single bright-blue star, Spica. Above Spica and 65 million light-years in the distance lurks the nearest cluster of galaxies. Five thousand "cities of suns," each with many billions of suns and planets, hover in this spot. It all appears as myriad gray blobs through backyard telescopes. This is the greatest concentration of objects in our part of the universe - yet there's no trace of it to the naked eye.
6. Every star in the night sky revolves around the center of the Milky Way. That pivot-spot floats in summer's southern sky at midnight. Earth and sun, moving at 144 miles per second, orbit that location every 230 million years.
7. Summer's brightest stars are blue-white Vega and orange Arcturus. One can also observe white, reddish and yellow stars, but none that are green. Green stars do not exist.
8. By day, the sky's real color is violet. But our eyes are so insensitive to that hue at the edge of the spectrum that our retinas are overwhelmed by the copious blue that's also present. Some insects can see the true color of the sky; we cannot.
9. Summer's most popular stargazing night is August 11/12, when the Perseid meteors blaze at a meteor-a-minute after midnight. All appear the same distance: between 60 and 100 miles away. None are closer and none farther, and all move at exactly 37 miles per second.
10. Moonless nights in September and October offers the year's best views of the Milky Way. This is our own disc-shaped galaxy, seen from our worm's-eye perspective. It's invisible from cities, but in rural regions like ours it dominates the entire sky. Some primitive cultures regarded it as the center of the universe.
11. Six constellations come from Greek mythology, and mostly appear in the fall. Not one - Perseus, Pegasus, Andromeda, Hercules, Cassiopeia and Cepheus - contains a single bright star. The Greek legends have been short-changed.
12. The most famous star cluster is the Pleiades or Seven Sisters. Average eyesight sees six stars. In dark sites, one counts between eight and 11. Nobody, oddly enough, sees exactly seven. The Dippers, too, are said to have seven stars when they don't. Reason? Seven was lucky in ancient times, while six and eight were not.
13. Psychologically, everyone exaggerates the moon's size. Few would guess that you'd need 180 full moons piled atop the other to stretch from horizon to zenith, or that it would require 10,000 packed together to fill the sky. A second, separate illusion makes the moon seem absolutely enormous whenever it's low.
14. Only three celestial bodies can cast shadows: Sun, Moon and Venus. If you count the weird, rapidly moving shadows from the occasional superbright meteor, that makes four.
15. Sunlight is a half-million times brighter than moonlight, and five billion times brighter than the most luminous stars. It causes pupils to contract to two millimeters and retinas to lose low-light sensitivity. This so underexposes stars that astronauts on the moon or in orbit see no stars in the black sky, except briefly when the sun is blocked behind the Earth.