Dealing with planets, galaxies, comets, meteors, and stars, astronomy is the science which studies the astral bodies. Astronomy also provides the basis for other physics-related sciences such as astrophysics and cosmology. The main staples of astronomy include: the solar system, nearby stars, asteroids, galaxies, and comets.

The Solar System


Newton's law of gravitation concluded that a force was present between the sun and each of the planets, which caused a strong attraction. The law also includes an explanation for smaller forces between the individual planets, and other bodies such as comets and asteroids. The oval shaped orbits of the planets around the sun are caused by interplanetary gravitational forces. The astronomical instrument, know as the telescope, is the only way of viewing these expected irregularities stipulated by Newton's theory.

Discovery of the individual elements of the solar system was accelerated with the use of the telescope. In 1781, British astronomer Sir William Herschel discovered Uranus. British astronomer John Couch Adams and French astronomer Urbain Jean Joseph Leverrier located Neptune independently in 1846. Clyde William Tombaugh mapped Pluto in 1930. Natural satellites are also being discovered at an alarming rate. Earth has 1 satellite; Mars, 2; Jupiter, 16; Saturn, more than 20; Uranus, 15; Neptune, 8; Pluto, 1. These numbers are expected to rise as more and more probes are being launched. Countless smaller bodies exist as stony and metallic meteroids.

Mercury, Venus, Mars, Jupiter, Saturn, and Uranus, have been approached by probes and satellites in order to gather physical and chemical data from these bodies. These missions, set in the 1970's and 1980's, have also helped determine the presence of rings around Jupiter and new moons orbiting Saturn and Uranus. The possibility of existence of life on other planets has been dismissed due to the information collected by these satellites. The data displays atmospheres which are inhabitable to life (too hot, cold
or dry).

Nearby Stars

Stars, once thought of as mere backdrops to the sun and other planets, have increased in importance with the invention of the telescope. Thanks to this magnificent instrument, astronomers of the present can experience the challenging aspect of astronomy that is the study of stars.

A star's distance from the earth has become basic knowledge to astronomers. The stars position is measured at six month intervals, when the earth is on opposite sides of its orbit. As the earth swings around the sun, the star appears to shift back and forth in the sky. This annual shift is called parallax. The parallax is then used to calculate the stars distance from the earth. The greater the parallax, the closer the star is to the earth. The second closest star, Alpha Centauri, is 260 000 farther from the earth than the sun.

The stars and the sun, being hot gaseous bodies, share similar qualities, but all differ from one another in various ways. The most crucial physical information are the star's intrinsic brightness, size, mass, and chemical composition. Even though stars may seem dimmer than the sun, some are intrinsically brighter, this brightness is lost through the distance to the earth. Ten percent of the 50 nearest stars with complete information are brighter, larger, and more massive than the sun. Studies show that the majority of stars are composed largely of hydrogen.

The more massive a star, the shorter its life span. Stars one and a half times more massive than the sun will pass through their entire life cycles much faster than the sun. Through the use of Optical telescopes, the life cycles of stars have been discovered. To start the star begins to condense from inside its "cocoon" generally composed of a thick molecular cloud. This condensation starts a period of heating followed by a long period as a main-sequence star. Near the end of the star's life it expands to a red giant state, and finishes by degenerating to a white dwarf after contracting back to a similar calm state of a main-sequence star.

Comets

From the Latin phrase stella cometa, meaning "hairy star", comets are cloudy bodies revolving around the sun. Although characterized by a long, luminous, tail this only occurs during the segment of the comet's orbit closest to the sun.

Compared to a "dirty snowball", the nucleus of the comet makes up most of its mass. It is a small