Evolution of the Universe

How have people's views of our universe changed over time? Beginning in the 2 century, people have had many theories as to what our universe looks like, what planets are in it, where the planets are, and much more. Before getting into the evolution of our universe, we must first define the universe. A universe is all the mater and energy, including the earth, the galaxies, and the contents of the intergalactic space, regarded as a whole. This means that our universe is the world in which we exist and prevail.

There have been many astronomers that have contributed to our modern view of the universe. Ptolemy, Copernicus, Brahe, Aristotle, Galileo, Newton, Kepler, Hippachirus, and Aristarchus have all made astronomical advances that have guided us in understanding our universe today.

All the astronomers above saw the universe differently. Bellow is a table showing the different models of the universe that were made and which astronomer believed in which model.

Geocentric model- a model of the universe that places Earth at the center

Heliocentric model- a model of the universe that places the sun at the center

Hippachirus was born in Nicaea in Bithynia, which is now present day Turkey. Hippachirus had a geocentric view of the universe. Even though he was lacking instruments and previous knowledge from other astronomers, he was able to make many predictions about the universe. He believed that the sun, the moon, Mercury, Venus, Mars, Jupiter, and Saturn, and the stars revolved around the Earth everyday. He also thought that the sun moved in a west-to-east direction according to the stars, but in a circle. He said that the vernal and autumnal equinoxes, which are the two points where the ecliptic and equatorial planes intersect, and the summer and winter solstices, which are the two points of the ecliptic farthest north and south from the equatorial plane, divide the ecliptic into four parts. Hippachirus was also the first to introduce the idea of the epicycle. Following in Hippachirus' footsteps was Ptolemy, who extended his work.

In 85 A.D in Egypt a boy named Claudius Ptolemy, Claudius meaning Roman citizenship and Ptolemy meaning resident of Egypt. Ptolemy’s belief in Hipparchirus’ geocentric theory led him to making the Ptolemaic of the universe. As he studied, he believed that the universe was a series of concentric spheres made of crystal-like, transparent substances, which he thought were heavenly bodies. The tenth sphere call the prime mover moved itself, thus moving the other spheres. Beyond the 10th sphere in the Ptolemaic system was heaven, where he believed God sent resided souls. He thought that God was at one end of the universe and that humans were in the middle of the universe. Ptolemy also did some work with epicycles and ecliptics. He said that each plane revolves in a synchronized motion along a circular path, called an epicycle; the center of the epicycle revolves around the earth on a larger circular path, called a deferent. The epicycle’s center weeps out equal angles along the deferent in equal times as seen from a point, the eqaunt, and the epicycle’s center is midway between the earth and the eqaunt creating an epicyclical model.

Born Nicholas Copernicus of Poland in 1473, Copernicus believed in the heliocentric model. Apposed to Ptolemy's ideas, Copernicus believed that the planets revolve around the sun and the moon revolves around the earth. He believed that the sun revolved around the earth because of its daily oration on its axis and the earth's trip around the sun each year. He put forth the ideas that the sun is a fixed point that the planets have to refer their motions to. Also, if the sun is assumed to be at rest and if the earth is assumed to be in motion, then the remaining planets fall into an orderly relationship increasing from the sun.

In the 4 century, Aristotle created a geocentric model of the universe. In the model, Earth was centered and was surrounded by revolving clear spheres that were attached to the sun and the planets with the outermost sphere containing the fixed stars.

Johannes Kepler was born in Germany in 1571. Kepler believed in the heliocentric universe. He thought that the planets’ orbits were not circular, bur elliptical with the sun at the end of the ellipse rather that the center. He believed that when the sun rotates it sweeps the planets around. Kepler used Ptolemy's equant theory to create an accurate elliptical model. What Kepler is most famous for is his three laws of planetary motion that are state as followed: All planets move about the sun in elliptical orbits having the sun as one of the foci; a radius vector joining any plant to the sun sweeps out equal areas in equal lengths of time; the squares of the sidereal periods of the planets are directly proportional to the cubes of their mean distance from the sun. His first law is basically a correction of Copernicus' model. His second law shows how a planet will speed up when it is nearing the sun and begin to slow down when it is retracting. His third law gives the exact relation by which planets move faster on orbits which are closer to the sun. His discoveries of the laws meat that Copernicus' universe had the sun actively pushing the planets around in noncircular orbits.

Brahe was born in 1546 and came from Danish descent. He modified the Copernican system where the plants move around the sun, which then moved around the earth. He said that the moon and sun circulated earth and that the rest of the planets orbited the sun.

Aristarchus is the man who started it all. He proposed the heliocentric earth theory.

Between the 2nd century and now, many people people's dedication to developing and accurate model of this world we live in have bee different. Mainly the positions of the planets, moon, and sun; and their movements have been the major changes over time.

Ecliptic- the apparent path of the Sun's annual motion relative to the stars, shown as a circle passing through the center of the imaginary sphere celestial sphere containing all the astronomical objects. Eclipses of the Sun or Moon can occur only when the Moon crosses the ecliptic

Equatorial- situated in the plane of an equator

Solstices- either of the two points on the ecliptic when the Sun reaches its northernmost or southernmost point relative to the celestial equator

Elliptical- in the shape or pattern of a geometric ellipse

Epicycle- in the Ptolemaic theory of the solar system, a circle that is followed by a planet, the circle itself being centered on a larger circle within which is the Earth. The epicycle accounts for irregularities of planetary motion in geocentric astronomy

Equant- a point

Elliptical- relating to ellipsis or containing an example of ellipsis

Main Menu

See Also

Main Menu