|
The Solar System is a collection of the Sun and its orbiting planets, moons, asteroids, comets, and perhaps undiscovered types of bodies. It is located about half-way along the Orion Arm of the Milky Way Galaxy, and is about 26,000 light years from the Milky Way's Galactic Center. It takes approximately 226 million years for the Solar System to orbit completely around the Galactic Center.
In its present form, the Solar System is about five billion years old. This is one-fourth to one-half the currently estimated age of the Universe itself.
The origin of the Solar System has always been a puzzle, but astronomers are learning more with time. In the 1700s, Laplace proposed his Nebular Hypothesis. This hypothesis stated that the Sun and planets were the condensed remains of an earlier lens-shaped nebula. In 1770, Buffon proposed his Catastrophic Hypothesis. This hypothesis stated that some large body had collided with the Sun, sending forth the planet masses as a result. Around 1900, Chamberlain and Moulton proposed their Planetesimal Theory. This conjectured that a second Sun passed close to our own, and its gravitational attraction caused our Sun to spew out great masses that condensed and became planets as they cooled. Currently, Steven Hawking believes that our Sun is a second- or third-generation sun. He conjectures that an earlier sun had to form, go through nuclear fusion to produce the heavier elements of the planets and other bodies, collapse, and explode as a supernova to give birth to the present Sun and other Solar System objects.
During Europe's Middle Ages, astronomers followed Ptolemy's hypothesis that the Earth was the center of the Solar System. In the late 1500s, Nikolaus Copernicus found that planetary orbits could be predicted by assuming that the planets revolved in circular orbits around the Sun. This was contrary to the time-honored belief that all planets and the Sun revolved around the Earth. In the early 1600s, Johannes Kepler found with careful telescope measurements that planetary orbits were not perfect circles, but were better described as elliptical orbits with the Sun at one focus.
In the late 1600s, Sir Isaac Newton demonstrated that planets, the Sun, and other bodies revolve around each other by mutual gravitational attraction. He also showed how objects revolve around their mutual center of gravity, which is closest to the largest of all rotating objects. He was able to use his new theory of gravitation to show how the planets naturally followed elliptical orbits around the Sun, as shown by Kepler.
The Solar System's center of gravity is known as the Solar System Barycenter. The Sun, being by far the most massive object in the Solar System, is always very near the Barycenter.
|