Wonders of the Sun
The sun is a star that dominates the planetary system with the gravitational effects of its mass. The sun supplies the earth with energy by the radiation of its electromagnetic energy. Because of its importance to the earth, the sun is a great star to study. There is no other star of the universe that can be studied in such indept detail. In order to study the features of the surface of the sun, one would need a telescope almost 30 km in diameter. This telescope would be put into space to avoid distortions caused by the atmosphere of earth.
A great amount of the studies of the sun such as stolstices, equinoxes, and eclipses dates back from the discovery of sunspots and the study of the physical properties were not until much later.
In 1611, a recently invented telescope was put to use which lead to the discovery of dark spots in the sun. This discovery was made by a man named Galileo, and it marked the beginning of new philosophical approach to the study of the sun. The sun was seen as a dynamic, evolving body and its properties were then able to be understood scientifically.
The sun emits energy in the form of radiation; this is a constant process. The sun, like most stars, is made up of 71% hydrogen, 27% helium, and 2% other elements. Near the center, the temperature is almost 16,000,000K and 150 times the density of water. The nuclei of single atoms interact, in the process of nuclear fusion. During this process, nuclei combine to make one helium nucleus and energy is then released in the form of gamma radiation. The nuclear "burning" of hydrogen in the core of the sun extends out to approximately 25% of the sun's radius.
Just above the surface of the sun is a slightly cooler gas. It absorbs some of the radiation from the visible surface of the sun. Only particular wavelengths of radiation are absorbed, however, depending on the atomic species present in the solar atmosphere. The lack of radiation at certain wavelenghts in the Franhofer spectrum of the sun is due to absorption of radiation by atoms of some of the same elements present on earth. This shows that the sun is made up of regular matter.
American astronomer George E. Hale discovered in 1908 that sunspots contain strong magnetic fields. A sunspot has a field strength of 2500 guass. Sunspots occur in pairs, with the two spots having magnetic fields that point in opposite directions: one into and one out of the sun. The sunspot cycle, in which the number of sunspots vary from low to high and then low again over 11 years, has been known since the 18th century. Each sunspot exists for only a few months.
A large amount of the sun's magnetic field is located outside the sunspots. The larger scale disturbance in the convection zone pushes much of field at and just above the photosphere, to the edges of the supergranulation cells. Radiation from the chromosphere, the layer above the photosphere, shows the pattern. In the supergranule boundaries, jets of material shoot into the chromosophere to an altitude of 4000 km in ten minutes! These "spicules" are caused by the combination of the disturbance and magnetic field at the edges of the supergranule cells.
The sun's past and future have been concluded from models of its structure. During its first 50 million years, the sun shrank to approximately its size now. Gravitational pull released by decreasing gas heated the interior, and when the core was hot enough, the contraction stopped and the nuclear burning of hydrogen into helium began. The sun has been in this stage of life for about 4.5 billion years.
There is enough hydrogen left in the sun to last for another 4.5 billion years. Once this fuel is depleted the sun will change. When the outer layers expand to orbit the earth or beyond, it will become a red giant star, slightly cooler than how it is now and 10,000 times brighter. It will stay a red giant for about half a billion years. The sun is not big enough to go through the consecutive nuclear reactions that will happen in the core as some stars can. After it becomes a red giant, it will shrink to a white star, about the size of earth, and slowly cool for several billion years.
| This page was written by Tamieka in the astronomy class of BCC/Broward County on July, 1998. The information was provided by The Encarta Encyclopedia 1996.> |