History of the Sun

For most of the time that humans have been on the earth, the sun has been regarded as a celestial oobject of special signifience. Many ancient cultures worshiped the sun, ans many more recognized its signifience in the cycle of life. Aside from its calendrical of postional importance in marking, for example ,solstices, equinoxes ,and eclipses the quantitative study of the sun dates from the discovery of sunspots, and the study of its physical properties was not initated until much later.

In 1611 Galileo,using the recently invented telescope, discovered dark spots on the sun Galileo discovery marked the beginning of a new philsophical approach to studying the sun. The sun was finally viewed as a dynamic, evolving body, and its properties and variation were thus able to understand scientically.

The next major break through in the study of the sun came in 1814 as the direct result of the use of spectroscope by the german physicist Joseph von Fraunhofer. A spectroscope breaks up light into its component wavelengths, or colors. Although the spectrum of the sun has been observed as early 1666 by the English mathematician and scientist Sir Isaac Newton, the accuracy and detail of Fraunhofer's work laid the foundation for the first attempts at a detail theoratical explanation of the solar atmosphere.

The total amount of enery emitted by the sun in the form of radiation is remarkably constant, varying by no more few tenths of 1 percent over several days. Th is enery output is generated deep within the sun. Like most stars, the sun is made up primarily of hydrogen. Near the center of the sun the temperature is almost 16,000,000 K and the density 150 times that of water. Under these conditions of the nuclei of the indiviual hydrogen atoms interact, undergoing nuclear fusion. In this process two hydrogen nuclei combine to make one helium nucleus, and energy is released in the form of gamma radiation. This energy is equivalent to that which would be released from the explosion of 100 billion one -megaton hydrogen bombs per second. The nuclear " burning" of hydrogen in the core of the sun extends out to about 25% of the sun's radius.

The sun's past and future have been inferred from theoratical models of stellar structure. During it's first 50 million years, the sun contracted to approximately its present size. Gravitational energy released by the collapsing gas heated the interior, and when the core was hot enough, the contraction ceased and the nuclear burning of hyrogen began in the core. The sun has been in this stage of its life for about 4.5 billion years.

Enough hydrogen is left in the sun's core to last another 4.5 billion years. When that fuel is exhausted the sun will change: As the outer layers expand to the orbit of the earth or beyond, the sun will become a red giant star, slightly cooler at the surface than at present and 10,000 times brighter. It will stay as a red giant, with helium-burning nuclear reactions in the core for only about half a billion years.