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FOR AGES 8 AND 9
INFORMATION - SPACE - SOLAR SYSTEM
Solar system is made up of objects, which orbit the Sun. The most important of these objects are the nine planets. The solar system also includes many smaller bodies, like moons of planets, rings of Saturn, and asteroids in the Asteroid belt.
The asteroid belt divides planets into two groups-inner planets and outer planets.
The inner planets are: Mercury, Venus, Earth, and Mars.
They are rocky and small.
The outer planets are: Jupiter, Saturn, Uranus, and Neptune.
They are gaseous and larger.
Some astronomers do not consider Pluto as the ninth planet. Instead, they think it is a large asteroid.
As of August 24, 2006 the International Astronomical Union (IAU) 26th General Assembly Resolutions 5A and 6A, the Solar System now consists of eight "planets". Mercury, Venus, Earth, Mars, Jupiter, Saturn, Uranus, and Neptune. Pluto, Ceres, and 2003 UB313 are members of a new class of objects called "dwarf planet". Pluto is considered as a proto-type of a new class of Trans-Neptunian Objects (TNOs).
Now how will you remember the eight planets?
The old mnemonic was "My Very Excellent Mother Just Sent Us Nine Pizzas."
The new mnemonic could be "My Very Extravagant Mother Just Served Us Nachos."
Planets travel in orbits around the Sun. If you look from above, they all move in counter-clockwise direction, but with different speed . Most of them move in same plane in nearly circular or elliptical fashion with different eccentricity.. The orbits of Mercury and Pluto are elongated and make a slightly tilted plane.
The length of time that the earth takes to complete one circle around the Sun is called a year. This time varies for different planets depending on their distance from the Sun. Mercury takes about 88 days to complete one circle. So its year has only 88 days (earth days). Pluto is far away planet and it takes about 250 earth years to complete its one circle. It means that its year is made up of 250x365=91,250 earth days. What a long year!
The Sun is one of the 200 billion stars of our galaxy, which is also known as the Milky Way. A galaxy is a group of stars scattered billions and billions of miles away from each other. All these stars in the Galaxy orbits the center. Our Sun takes about 250 million years to complete one orbit. Our galaxy is spiral shaped with central bulge, called the nucleus, and a thin disk which has two spiral arms in it. The Sun with its whole solar system lies in one of the spiral arms some 30,000 light years from the center - about two third from the center to the edge of the galaxy. A light year is the distance that light travels in a year at a speed of 186,000 miles per second; that is about 6 trillion miles per one light year. Light would take about 100,000 years to cross the galaxy.
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