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Astronomy 101 - Solar System - Outer Solar System

Lesson 10: Completing Our Visit Close To Home


Jupiter - Astronomy 101 - Solar System - Outer Solar System


Our final lesson will concentrate primarily on the Outer Solar System, including the four Jovian gas giants; Jupiter, Saturn, Uranus, and Neptune as well as an unusual smaller planet called Pluto. We'll wrap up with some final information, comments, and sources for further study.

Jupiter, the fifth planet from the sun, is also the largest in our solar system. Its average distance is approximately 480 million miles, which is about five times the distance from Earth to the Sun. Unlike the terrestrial planets, Jupiter is a large ball of gas, tightly condensed. It has no surface, though it may have a core composed of comet-like rock-forming minerals, but the core makes up less than 5 percent of the planet's mass, which is approximately 318 times the mass of Earth. Gravity at the top of the clouds in Jupiter's atmosphere is about 2.5 times Earth's gravity

Jupiter takes about 11.9 Earth years on its journey around the sun, and its day is only about 9.9 hours. It is the fourth brightest object in Earth's sky, after the Sun, the Moon, and Venus. It is more than three times brighter than Sirius, the brightest star, and can be seen easily with the naked eye, though binoculars or a telescope may show details, like the giant red spot, or Jupiter's rings.

The second largest planet in our solar system, Saturn, is the sixth from the sun. Another Jovian planet, Saturn is also primarily condensed gas, with a minute rocky core. The contraction of the planet caused the enormous pressure of Saturn's atmosphere causes so much heat, that it radiates as much into space as it receives from the sun. Saturn is perhaps best known for its rings, which are known by their letter designation, indicating when they were discovered. From the planet outward, they are D, C, B, A, F, G, and E rings, which are comprised of hundreds of thousands of ringlets.

Viewed from earth, Saturn appears as a yellowish object and can be easily viewed by the naked eye. With a telescope, the A and B rings are easily visible, and under very good conditions the D and E rings can be seen. Very strong telescopes can distinguish more rings, as well as the nine satellites of Saturn.

Uranus is the seventh most distant planet from the sun, with an average distance of 1.78 billion miles. It has a mass 14.5 times greater than Earth, with a volume that is 67 times greater. Uranus has a rocky core, completely covered with water, mixed with rocky particles. It has an atmosphere of hydrogen, helium, and methane. Despite its size, Uranus's gravity is only about 1.17 times that of Earth. A Uranus day is about 17.25 Earth hours, while its year is 84 Earth years.

Uranus was the first planet to be discovered using a telescope. Under ideal conditions, it can barely be seen with the unaided eye, but should be clearly visible with binoculars or a telescope. Like the other "Jovian" planets, Uranus has rings, 11 that are known. It also has 15 moons discovered to date. Ten of these were discovered when Voyager 2 passed the planet in 1986.

The last of the gas giant planets in our solar system is Neptune, fourth largest, and usually eighth in distance from the sun. (Read about Pluto below to find out more about that.) Its composition is similar to Uranus, with a rocky core and huge ocean of water. With a mass 17 times that of Earth, it's volume is 72 times Earth's volume. Its atmosphere is composed primarily of hydrogen, helium, and minute amounts of methane. A day on Neptune lasts about 16 Earth hours, while its long journey around the sun makes its year nearly 165 Earth years.

Neptune is occasionally barely visible to the naked eye, and is so faint, that even with binoculars looks like a pale star. With a powerful telescope, it looks like a green disk. It has four known rings and 8 known moons. Voyager 2 also passed by Neptune in 1989, nearly ten years after it was launched. Most of what we know was learned during this pass.

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