Observing the Solar System

??Why is Pluto no longer a planet?? According to the new definition, a full-fledged planet is an object that orbits the sun and is large enough to have become round due to the force of its own gravity. In addition, a planet has to dominate the neighborhood around its orbit. Pluto has been demoted because it does not dominate its neighborhood. Charon, its large "moon," is only about half the size of Pluto, while all the true planets are far larger than their moons.

Ideas of the revolving planets Greek astronomers believed that the Earth is the center of the universe, which is called a geocentric (geo means Earth) system. Copernicus in the 1500’s believed that the sun was the center of the universe, a heliocentric (helio means sun) system. Meaning the planets revolve around the sun.

Why do the planets stay in orbit? INERTIA and GRAVITY Inertia is a tendency of a moving object to continue in a straight line or a stationary object to remain in place. The more mass an object has, the more inertia it has. The force of gravity attracts all objects towards each other. No one is for sure how gravity works or why it is present. As the planets are in orbit around the sun the sun’s gravity pulls on them while their inertia keeps them moving ahead.

Also known as a “long haired star” in Greek Comets are chunks of ice, gas, water and dust. Comets look like they have tails because as it travels through space it warms up and gives off a cloud of gas around it. They follow an orbit around the sun. As they get closer to the sun they generally speed up.

Asteroids Next to Moon in size They are irregular shaped, some resemble lumpy potatoes, while others look like rocks. Asteroids are made up of iron, nickel, stone or a combination of them. It is believed that asteroids are actually parts of the solar system that never joined together. Most asteroids are in the asteroid belt, a region that lies between the orbits of Mars and Jupiter. Like comets, asteroids orbit the sun.

Meteors – Shooting Stars Meteor– streak of light formed by a space rock and dust burning up as it plunges into Earth’s atmosphere Known as meteoroids when in space.

Meteors Cont…….. When and IF this rock strikes Earth it is a meteorite. Most burn up completely before reaching the ground. This occurs when Earth passes through the tail of a comet or a cloud of dust left behind by a broken-up asteroid.

Stars Like the sun, stars are huge spheres of glowing gas. They are made up of mostly hydrogen and helium. They make energy by nuclear fusion causing the stars to shine brightly. The main characteristics to classify stars are size, temperature, and brightness.

Birth and Death of Stars All stars begin their lives as nebulas, a large amount of gas and dust spread out in an immense volume. Gravity then pulls some of the dust and gas together causing a contracting cloud. A star is born when the contracting gas and dust become so hot that nuclear fusion starts.

Black holes When a large star undergoes a supernova explosion it may collapse in on itself. The singularity is a region where the force of gravity is so strong that light cannot escape.

Three main classes of galaxies 1. Spiral Galaxy– have arms that spiral outward like pinwheel 2. Elliptical Galaxy– looks like a flattened ball. They lack gas and dust not allowing new stars to form. 3. Irregular Galaxy– does not have a regular shape

Milky Way due to “milky” appearance

Reasons for Life on Earth Protective atmosphere Breathable atmosphere Liquid water Suitable temperature range