Types of Planets and Stars John Phillips Mrs. Cooper/NWRMS Science Bowl September 1, 2014

History of Astronomy and Modern Astronomy Astronomy is the study of the sun, moon, stars, planets, comets, gases, galaxies, dust, and non-earthly bodies. Pythagoras, a Greek philosopher and mathematician, recorded his first theories about stars. Some of his best theories were about the “morning star” and the “evening star,” which was Venus, and the idea that the Earth was in motion. Modern astronomy defines a star as “a self-luminous body consisting of gas held together by gravity in which is generated by nuclear fusion.” It defines a planet as “a non-luminous celestial body larger than an asteroid or comet illuminated by a star, which it revolves around.”

Young Stars Protostars -- what is present before a true star forms. It is a collection of gases and dust that have collapsed down from large molecular clouds. This phase lasts about 100,000 years. The heat comes from gravitational heating, as nuclear fusion has not started yet. T Tauri stars -- do not have enough pressure and temperature to generate nuclear fusion, but they resemble main sequence stars. They are about the same temperature, but they are slightly bigger than main sequence stars. They have more sunspots and X ray flares as well as very powerful stellar winds. They will remain like this for about 100 million years.

Middle-Aged Stars Main Sequence Stars -- make up the majority of stars in the universe. Earth’s sun is a main sequence star. These stars vary in size, mass, and brightness, but they all convert hydrogen into helium, also known as nuclear fusion. While our sun will spend 10 billion on its main sequence, a star ten times as massive will stick around for only 20 million years. Red Dwarf -- most common stars in the universe. These stars are main sequence stars that have very little mass and are cooler than stars like Earth’s sun. Because of this, they use hydrogen more slowly, which allows them to burn longer than most stars. Its lifetime, 80-100 billion years, is older than the universe. Super Giants -- because of their size, they use hydrogen more quickly than most stars, and they live only 10-20 million years. When they run completely out of fuel, they explode in a violent supernova, which disintegrates the star.

Old Stars Red Giant – the main sequence star runs out of hydrogen at its core, it swells up to take in extra elements such as helium in a small band around the star. White Dwarf – if a main sequence star does not explode in a super nova, it runs out of fuel and no more nuclear fusion occurs within the star. These stars are basically stars that are cooling down.

Terrestrial Planets Terrestrial planets are known as the inner rocky planets. These planets are small in size and mass and have high density. They are made mostly of rock and metal, and they generally have solid surfaces with few to no moons. Terrestrial planets are located close to the sun like Mercury, Earth, and Venus.

Jovian Planets Jovian planets are knows as the gas giants. These planets are high in size and mass and have low density. They are made mostly of hydrogen and helium with no solid surface and many moons. These planets can have rings around them. Jovian planets are located further from the sun than terrestrial, but are not necessarily colder. Examples of these planets are Jupiter and Saturn.

Ice Giants Ice giants have a lower mass, size and hydrogen/helium content than Jovian planets. These planets have rings much like the Jovian planets. They are located in the furthest reaches of the solar system. Examples of these are Neptune and Uranus, and for many scientists, Pluto, which some feel is still a planet.

Works Cited Cain, Fraser. "Types of Stars." Universe Today RSS. Universe Today, 28 Jan. 2009. Web. 06 Aug. 2014. "Our Solar System." The Solar System: The Sun, Planets, Dwarf Planets, Moons, Asteroids, Comets, Meteors, Solar System Formation. National Earth Science Teachers Association, 2012. Web. 06 Aug. 2014. "Types of Solar System Planets." Types of Solar System Planets. The Nebraska Astronomy Project/University of Nebraska, 12 June 2014. Web. 06 Aug. 2014.