The Structure Of Stars

The internal structure of normal stars is fairly simple because only a few physical principles are involved in the determination of the structure of a gaseous object. This simplicity is summed up in a simple principle, the Russel-Vogt theorem. For stars of like composition, the structure and observable properties depend on a single parameter such as the star's mass. Alternatively, the Russell-Vogt theorem may be expressed as follows The equilibrium structure of an ordinary star is determined...

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At much lower temperatures, below 300 K, the most common elements, hydrogen, nitrogen, carbon, and oxygen, formed ices of H2O, NH3, CH4, and CO2. Carbonaceous chondrites (with chon-drules, or spherical grains that never were melted in later events) are the direct evidence that grain formation took place in the early solar system, with a subsequent amalgamation of these small solid particles into larger and larger objects. Given the range of temperature in the protoplanetary nebula,...

Q

Pythagoras (circa 580-500 B.C.), who is credited with summarizing previously developed ideas of geometry, is also credited with proposing the idea of a spherical Earth and Moon. He developed this concept from studying the pattern of shadows on the Moon during eclipses. Pythagoras also correctly deduced the cause of the phases of the Moon. Aristotle (circa 384-322 B.C.) believed that the Sun moved around Earth. His belief in a stationary Earth was probably the result of his familiarity with the...

The Milky Way Galaxy

The Milky Way Galaxy, or simply the Galaxy, is a typical example of a galaxy, a large, independent system of stars, star clusters, and interstellar material. By studying the Milky Way, we can better understand galaxies as a whole. The Milky Way can be identified as a spiral galaxy because of the pinwheel-shaped interstellar material that traces out a spiral pattern in the plane of the Galaxy. The Galaxy is actually made up of two distinctly different spatial distributions of stars, one of which...

The Solar System

The solar system consists of the Sun, nine planets, some 60 or so moons, and assorted minor materials (asteroids, meteoroids, comets, dust, and gas). All of these objects are tiny in comparison to the distances that separate them. Imagine the solar system scaled down such that distances to the planets could be spaced along a 10-kilometer hiking trail. On such a scale the Sun would be represented by a ball only 2.3 meters in diameter. The distribution along the trail and the model sizes for each...

Formation And Evolution Of Stars

Pre Main Sequence Stars Evolution

Interstellar space is filled with diffuse gas and dust. Relatively denser and cooler regions, up to 50 pc in diameter and with a million solar masses, are filled with molecules. In these molecular clouds, shock fronts from nearby star formations or a supernova explosion or some other global gravitational disturbance may begin the process of self-gravitational contraction, leading to the formation of new stars. The earliest stages of pre-main sequence evolution are not directly observable,...