The largest is the Biosphere
Stars<span> start their lives as clouds of dust and gas. ... But if the body has sufficient </span>mass<span>, the collapsing gas and dust burns hotter, eventually reaching </span>temperatures<span> sufficient to fuse hydrogen into helium. The </span>star<span> turns on and becomes a </span>main sequence star<span>, powered by hydrogen fusion
Tangerines AmbitiousThere are a few hundred billion stars in our galaxy, the Milky Way and billions of galaxies in the Universe. One important technique in science is to try and sort or classify things into groups and seek out trends or patterns. Astronomers do this with stars.
So far we have discussed the luminosity and colour or effective temperature of stars. These can be plotted to form what is one of the most useful plots for stellar astronomy, the Hertzsprung-Russell (or H-R) diagram. It is named after the Danish and American astronomers who independently developed versions of the diagram in the early Twentieth Century.
In an H-R diagram the luminosity or energy output of a star is plotted on the vertical axis. This can be expressed as a ratio of the star's luminosity to that of the Sun; L*/Lsun. Astronomers also use the historical concept of magnitude as a measure of a star's luminosity. Absolute magnitude is simply a measure of how bright a star would appear if 10 parsecs distant and thus allows stars to be simply compared. Just to confuse things, the lower or more negative the magnitude, the brighter the star. By definition a star of magnitude 1 is 100 × brighter than one of magnitude 6. Our Sun has an absolute magnitude of + 4.8.
i hope this helps </span>
