Everyone who has interest for astronomy has heard a word deepsky. What is meaning of this charming word? Deepsky is a one field of amateur astronomy, which contains all objects which are outside our solar system. Deepsky-objects are also objects that have surface that we can see. Deepsky-objects has been grouped by their character, these groups are open clusters, globular clusters, planetary nebulae, supernova remnants, bright nebulae, dark nebulae and galaxies.
Galaxy is a system of stars, dust, and gas held together by gravity. Galaxies are scattered throughout the universe. They range in diameter from a few thousand to half a million light-years. A light-year is the distance light travels in a year--about 5.88 trillion miles (9.46 trillion kilometers). Large galaxies have more than a trillion stars. Small galaxies have fewer than a billion. Astronomers have photographed millions of galaxies through telescopes. They estimate that there are about 100 billion galaxies in the universe.
Galaxies are distributed unevenly in space. Some galaxies are found alone in space, but most are grouped in formations called clusters. Clusters of galaxies range in size from a few dozen members to several thousand.
There are three types of galaxies. These types are called spiral galaxies, elliptical galaxies, and irregular galaxies. A spiral galaxy is shaped like a disk with a bulge in the center. The disk resembles a pinwheel, with bright spiral arms that coil out from the central bulge. The Milky Way is a spiral galaxy. Elliptical galaxies range in shape from almost perfect spheres to flattened globes. The light from an elliptical galaxy is brightest in the center and gradually becomes fainter toward its outer region. Irregular galaxies have no particular shape.
Star clusters may be either ball-like or of irregular shapes. Ball-like clusters, called globular clusters, contain from 10,000 to a million stars densely packed together. About 100 globular clusters lie around the center of the Milky Way. The stars in globular clusters are among the oldest in our galaxy. Irregularly shaped clusters, called open clusters or galactic clusters, have from less than a hundred to a few thousand stars. They lie within the main "pancake" of the Milky Way. They include some of our galaxy's youngest stars.
Today, most astronomers use the term nebulae only for the clouds of dust and gases in the Milky Way and other galaxies. They classify these masses into two general types: diffuse nebulae and planetary nebulae. Both types are also called gaseous nebulae.
Diffuse nebulae are the larger of the two types. Some diffuse nebulae contain enough dust and gases to form as many as 100,000 stars the size of the sun.
Planetary nebulae are ball-like clouds of dust and gases that surround certain stars. They form when a star begins to collapse and throw off the outer layers of its atmosphere. When viewed through a small telescope, this type of nebula appears to have a flat, rounded surface like that of a planet.