If the Sun were compressed to a diameter of just four miles (6 km), its escape velocity would equal the speed of light -- 186,000 miles (300,000 km) per second. Since nothing can travel faster than light, no matter or energy could escape its surface.
When a star like the Sun dies, it casts its outer layers into space, leaving its hot, dense core to cool over the eons. But some other types of stars expire with titanic explosions, called supernovae. A supernova can shine as brightly as an entire galaxy of billions of "normal" stars. Some of these explosions completely destroy the star, while others leave behind either a super-dense neutron star or a black hole -- an object with such powerful gravity that not even light can escape from it.
The words astronomers use to describe stars evoke the fairy tales of childhood: white dwarfs, red giants, red dwarfs, and blue giants, among others.
The characteristic that distinguishes a giant star from a dwarf star is size, which depends on the star's mass and its stage in life. The characteristic that distinguishes a red star from a blue star is temperature. When an iron bar is first removed from a blacksmith's forge, it appears white hot. As it cools, its color changes from bright orange to dull red, then black.
A star's color provides a direct measurement of its surface temperature; the hottest stars shine blue-white, while the coolest are dull orange or red. In turn, the temperature indicates how much energy a given area of the star's surface radiates into space every second. When that is multiplied by the star's total surface area, it tells us the star's luminosity -- a measurement of how much energy it radiates into space every second.
One of the great mysteries of the ancient world was the nature of the stars. As people watched these twinkling lights wheel across the sky night after night, year after year, they thought of them as the eyes or souls of the dead, as candles flickering against a tall background, or as holes in the dome of the sky that allowed the light of heaven to shine through.
Physicist Jean-Baptiste Biot investigated the L'Aigle events. He found that people in other villages had seen a bright fireball in the sky just before the explosion. The sequence of events left no doubt that the meteorites came from a celestial source.
Beyond your own two eyes, the next best piece of equipment for the star hunter is a good pair of binoculars. They are inexpensive, highly portable, and strike a wonderful balance between magnification and light-gathering power; the wide view provided by a pair of binoculars also counters the inevitable confusion of finding a target in a crowded starfield.
Find a state park or other safe, accessible spot. And try a night without moonlight, so you can see meteors and the Milky Way.
What you see in the night sky depends on your location, the season, and the time.
Planets orbit the Sun, so they change position when compared to the stars. The planet Venus, sometimes called the "evening star" or "morning star," is the second-brightest object in the night sky — only the Moon is brighter. Jupiter, Mars, and Saturn often are visible later at night than Venus. Planets reflect a steady light, unlike the "twinkling" stars, which are much farther from Earth.
