Astronomy concepts and applications

¶ … ancient Greeks contributed much to our modern knowledge of the universe. Still, there concepts often differed because of the lack of scientific technology we have today. One of the prominent ideas of the Greeks that have been discredited was the geocentric view of the universe. Thus, all the planets and even the sun all orbited the Earth which was at the center. This was a view that placed the Earth at the very center of the universe. Ptolemy helped mold the concept and accounted for the motions of the celestial bodies through explaining that each planet and star moved around the universe in circles, known as epicycles. Planets moved at different speeds, depending on what point they were on in their epicycle. Thus, although the Earth is not the center of the universe, Ptolemy contributed to the concept of orbiting bodies.

Two minor members of the solar system include asteroids and comets. These are members of the solar system which have their own unique orbits, but cannot be classified as a planet or a start. Asteroids are small rocky objects that orbit the sun, in a similar fashion as a planet would. There is a major grouping of them in the asteroid belt, although some can be knocked out of their orbits and be a danger to planets. Comets are similar, but are actually made of frozen ice and dust rather than rock. They too have an orbit around the sun. They are known for their fiery tales of gas and dust that can light up the night sky.

Moving into a modern image of astronomy was a long and difficult process. There have been many great minds who have contributed to this progress. One of the major proponents of a heliocentric model in its early stages was Nicolaus Copernicus. He fought the conservatism of the Church in order to put forward the radical idea that the solar system had the sun at the very center. Moreover, Tycho Brahe was another figure that challenged the traditional Greek system. He found evidence that the universe was constantly changing, rather than staying exactly the same. He took observations which showed there were newer stars and also that comets actually crossed through the celestial spheres, and did not occur below Earth's atmosphere. Johannes Kepler was a mathematician who calculated a more realistic image of planetary motion. According to Kepler, there were three major laws of planetary motion. Orbital planes were ellipses, and not circles, these ellipses were at equal lengths during specific periods of time, and finally that the square of an orbital period holds a correlated proportion to that planet's orbit's semi-major axis. Galileo Galilei played another major role and vastly improved the telescope, allowing future astronomers to make much more accurate calculations because of improved observations. Through his updated telescope, he was able to observe and record the phases of Venus as well as discover several of Jupiter's larger moons. Sir Isaac Newton was another major figure that helped create the ideas of modern astronomy. Through his work in physics, Newton created his theory of the laws of motion and the concept of gravity. The laws of motion and gravity became a way to understand and explain the movements of the planets and other celestial bodies. Without these men's great achievements, modern astronomy would be much different than it is today.

Planets can be either Jovian or terrestrial. There are a number of major differences between these two types of planets. Terrestrial planets are rocky masses that have solid surfaces, often made of rock and other hard substances and minerals. Some of these planets are Mercury, Venus, Earth, and Mars. These planets tend to be much smaller than their Jovian counterparts and are located closer to the sun. These planets made of rock and hard metals are incredibly dense and have no rings with fewer moons and other satellites. On the other hand Jovian planets are made up of thick balls of gasses. These planets are much larger than terrestrial planets. They are often composed of Hydrogen and Helium gasses that swirl around the planet in massive cloud-like atmospheres. These huge planets have much lower densities, a greater chance of having rings and more satellites that orbit them. Such planets include Jupiter, Saturn, Uranus, and Neptune.