Stars
STARS ARE BODIES of Hot glowing of gas that are born in nebulae. They very enourmously in size, mass, and temperature, and about 450 times smaller to voer 1,000 times bigger than that of the sun; masses ranger from about 12th to over 50 soloar masses and surface temperaturs range from about 3,000'C to over 50,000'C. The colour of a star is deternmind by its temperature: The hottest star are blue and the coolest are red. The Sun, with the surface temperatur of 5,500"C , is between these extremes that appears yellow. The energy emitted by a shining star is produces by a nuclear fusion in the star's core. The brightest of a star is measured in magnitures - the brighter the star the lower its magnitudes. There are two types of magnitudes: Apparent Magnitudes which is is the brightest seen from Earth and absolute Magnitudes which is the brightness that would be seen from a standard distance of 10 parasecs (32.6 light years). The light emitted by a star maybe split to form a spectrum containing a series of dark lines. (absorption lines). The pattern of lines indicate the presence of particular chemical elements, enabling astronomers to deduce the composition of the star's atmosphere. The Magnitude and spectral type (colour) of stars may be plotted on a graph called a Hertzsprung - Russel well defined groups. The principal groups are main sequence stars (those which are fusing hydrogen to form Helium), giants, supergiants, and white dwarfs.
