STARS

 STARS

         When we look at stars in the night sky, we are looking back in time. Many stars formed millions, if not billions, of years ago. Further more, the starlight that reaches our eyes left those faraway stars some time ago-ranging from a few minutes ago (the sun) to four years ago (Alpha Centauri, the sun's nearest star neighbor) to a much longer time ago (objects at the edges of our galaxy).

          We measure these distances in light years. One light-year is equivalent to approximately 6 trillion miles, or the distance light travels in one 365-day Earth year. Alpha Centauri, at 25 trillion

miles from Earth, is about 4 light-years away. The light we see today from the Andromeda Galaxy left it two and a half million years ago: Andromeda is 2.5 million times 24 trillion miles away.

           Stars, which are balls of (mostly the gases hydrogen and helium), emit radiation. They create energy by fusing hydrogen and t into helium in their cores. We see the resulting energy as starlight.

             Astronomers classify stars based on their size, temperature, color, and luminosity. Size in this case relates to mass rather than linear measurement, such as diameter. Stars start the same way, but their lives play out according to their size and mass. The mass of a star determines all of its other characteristics, including how hot it is, what color it is, and how long it will live. Massive stars are hot and blue. whereas small stars are cool and red.

SIRIUS, THE DOG STAR

 Blue-white dwarf in constellation Canis Major

CANOPUS

Yellow-white supergiant in constellation Carina

ALPHA CENTAURI

 Triple star in constellation Centauris

ARCTURUS

Orange-colored giant in constellation Boötes

VEGA

Blue dwarf in constellation Lyra

CAPELLA

Four-star cluster in constellation Auriga