Discovery Space: The Starry Sky
Light given off by stars is often outshone by light sources on Earth. Yet, anyone away from the big cities and looking up to the night sky can enjoy the stellar sparkle in all its glory.
The sky is full of stars even during the day; however, only one of them-the sun- is actually visible, because it outshines all the others. The stars and planets visible in the night sky change with the annual trajectory of the Earth around the sun.
People have long tried to recognize some order among the stars visible in the night sky. Thousands of years ago, people around the world traced imaginary lines between bright stars to create figures of their gods and mythological characters. Each culture thus developed its own constellations. Today, the International Astronomical Union (IAU) has set 88 con-stellations as standard. Different constellations are visible depending on the time of year and one’s location.
Celestial poles
The celestial poles are points on the celestial sphere in the direction of the Earth’s axis. Because the Earth revolves around this axis, the stars seem to rotate in circles around the celestial poles. At the Earth’s Poles, these circles appear parallel to the horizon. Elsewhere, the stars rise and set along the horizon, just like the sun and the moon.
Stars and planets
Stars appear variously bright, because they radiate with different intensities and they are at different distances from the Earth. Often they also appear to be trembling or sparkling, with their brightness flickering rapidly. Planets are easy to distinguish from stars in the night sky, because they do not twinkle at all or only very little. The twinkling of stars is caused by schlieren—optical inhomogeneities in the Earth’s atmosphere caused by air at different temperatures.
Because stars are so far away, they appear to us essentially as points of light. This means that their position in the night sky can be distorted by atmospheric turbulence, which appears to us as twinkling. Since planets are much closer to us than stars are, they appear as disks in the sky. This means that variations in brightness are spread out equally over the entire disk area, negating schlieren effects. Venus, Mars, and Jupiter are particularly easy to recognize because of their brightness.
THE NAMES OF STARS
The brightest stars have proper names, which often come from Arabic Later, they were assigned Greek letters—usually in alphabetical order in the sequence of their brightness—with the Latin name of the constellation added on.
Roman letters and numbers have also been used Be cause of the multitude of stars, most are given catalog numbers and only some are named after astronomers.
BASICS
STARS VISIBLE with the naked eye be-long to our own galaxy, the Milky Way system.
SIRIUS is the brightest star in the night sky. It belongs to the Canis Major (Large Dog) constellation and it is 8.6 light-years away.