Planets (science Matters)

Studying Planets Much can be seen in the sky on a clear night. Some objects in space pass by the twinkling stars and slowly travel across the sky. Moving space objects are usually planets. The word planet comes from the Greek word y which means "wanderer." Earth is one of the nine planets in our solar system. All of the planets travel around the Sun. The nine planets are Mercury, Venus, Earth, Mars, Jupiter, Saturn, Uranus, Neptune, and Pluto. • There are many more planets in the universe than the nine planets of our solar system. e I Planet Facts id you know that Earth is the only planet known o support life in our solar system? There are many other interesting facts about the nine planets. Mercury is the closest planet to the Sun. Venus is the brightest planet. Earth is the densest space object in our solar system, Mars is the second-closest planet to Earth. Jupiter is the largest planet. Saturn is known for its colorful rings. Uranus has rings and spins on its side. Neptune is surrounded by thick gases. Pluto is the smallest planet. Planets in the Past The ancient Aztec peoples watched and studied the planets. They prayed to the objects they saw in the sky as gods. Venus was the most important planet for the Aztecs. The planet Venus represented the god Tlahuizcalpantecuhtli. This long name means "Lord of the House of Dawn." • The Aztecs held festivals for the planet Venus at certain times of the year. e I Planet Names The name Earth comes from an English word that pneans "ground" or "soil." The other planets are named after Roman or Greek gods. MERCURY VENUS inessenger god BT goddess of love and beauty EARTH ground or soil MARS god of war JUPITER king ofthe gods SATURN ^ Ç ! ! ! ! ^ URANUS r of farming god ofthe sky NEPTUNE god ofthe sea PLUTO god ofthe underworld Planet Parts Earth, Mars, Mercury, and Venus are called terrestrial planets. They consist mainly of rock. Some of these planets have a thin atmosphere. Others have no atmosphere. Jupiter, Neptune, Saturn, and Uranus are made up mostly of gas. They are called gas giants. The atmospheres of these planets are thousands of miles thick. Pluto is made up of ice and rock. Its atmosphere is lost as quickly as it is created. Earth's atmosphere is mostly made up of gases. I Planet Sizes i.e nine pranets are different sizes. Jupiter is the irgest planet in our solar system. Pluto is smaller lan Earth's moon. A diameter is a measurement of a circle. It measures a straight line passing through the center of a circle, from one side to the other. The nine planets each have different diameter lengths. PLUTO: 1,485 miles (2,390 km) MERCURY: 3,031 miles (4,878 km) MARS: 4,220 miles (6,791 km) VENUS: 7,520 miles (12,102 km) EARTH: 7,926 miles (12,756 km) URANUS: 31,814 miles (51,200 km) NEPTUNE: 34,504 miles (55,529 km) SATURN: 74,898 miles (120,537 km) JUPITER: 88,846 miles (142,984 km) I I Planets on the Move The nearly circular path that a planet makes around the Sun is called an orbit. All planets travel counterclockwise. Most planets' orbits are elliptical. This means that they are not quite perfect circles. The time that it takes a planet to complete a full orbit is the length of its year. Mercury takes only 88 Earth days to travel around the Sun. One year on Mars is almost as long as 2 Earth years. It takes 248 Earth years to equal 1 year on Pluto. 5 • The force that keeps the planets in our solar system orbiting the Sun is called gravity. i I •pinning in Spa Did you know that the planets spin? While each planet orbits the Sun, it also spins like a top. <