The solar system

 The Sun is the closest star to Earth and is the center of our solar system. A giant, spinning ball of very hot gas, the Sun is fueled by nuclear fusion reactions. The light from the Sun heats our world and makes life possible. The Sun is also an active star that displays sunspots, solar flares, erupting prominences, and coronal mass ejections.It appears to have been active for 4.6 billion years and has enough fuel to go on for another five billion years or so. At the end of its life, the Sun will start to fuse helium into heavier elements and begin to swell up, ultimately growing so large that it will swallow the Earth. After a billion years as a red giant, it will suddenly collapse into a white dwarf  – the end product of a star like ours. It may take a trillion years to cool off completely.

Mercury is the planet closest to the Sun in our Solar System. This small, rocky planet has almost no atmosphere. Mercury has a very elliptical orbit and a huge range in temperature.It’s hotter than an oven; during the long night (the same length), the temperature is colder than a freezer. Mercury is so close to the Sun that you can only see it near sunrise or sunset. There are no seasons on Mercury. Seasons are caused by the tilt of the axis on the planet’s orbit. If you were on the surface of Mercury, the Sun would look almost three times as big as it does from Earth! This is the symbol of the planet Mercury. Mercury was named after Mercury, the mythical Roman winged messenger and escort of dead souls to the underworld. It was named for the speedy Mercury because it is the fastest-moving planet.

Venus is the second planet from the sun in our solar system. It is the hottest planet in our Solar System. This planet is covered with fast-moving sulphuric acid clouds which trap heat from the Sun. It’s thick atmosphere is mostly carbon dioxide. This is a planet on which a person would asphyxiate in the poisonous atmosphere, be cooked in the extremely high heat, and be crushed by the enormous atmospheric pressure. Venus is also known as the “morning star” or the “evening star” since it is visible and quite bright at either dawn or dusk. It is only visible at dawn or dusk since it is closer to the sun than we are. Venus rotates VERY slowly. Each day on Venus takes 243 Earth days. A year on Venus takes 224.7 Earth days. It takes 224.7 Earth days for Venus to orbit the sun once. Venus rotates in the opposite direction of the Earth (and the other planets, except possibly Uranus). Looking from the north, Venus rotates clockwise, while the other planets rotate counterclockwise. From Venus, the Sun would seem to rise in the west and set in the east (the opposite of Earth). No one knows why Venus has this unusual rotation. Venus is the hottest planet in our Solar System. This is the symbol of the planet Venus. Venus was named after the Roman goddess of love.

The Earth is the third planet from the Sun in our Solar System. It is the planet we evolved on and the only planet in our Solar System known to support life. The Earth is the fifth-largest planet in our Solar System (after Jupiter, Saturn, Uranus, and Neptune). The Earth has one moon. The moon may have once been a part of the Earth; it may have been broken off the Earth during a catastrophic collision of a huge body with the Earth billions of years ago. The coldest recorded temperature was  on the continent of Antarctica (Vostok in July, 1983). The hottest recorded temperature was on the continent of Africa (Libya in September, 1922).

  Mars, the red planet, is the fourth planet from the sun and the most Earth-like planet in our solar system. It is about half the size of Earth and has a dry, rocky surface and a very thin atmosphere. The north and south poles of Mars are covered by ice caps composed of frozen carbon dioxide and water. Mars has 2 tiny moons, Phobos and Deimos. They were probably asteroids that were pulled into orbit around Mars. This is the symbol of the planet Mars. Mars was named after the Roman god of war.

Jupiter is the fifth and largest planet in our solar system. This gas giant has a thick atmosphere, 39 known moons, and a dark, barely visible ring. Its most prominent features are bands across its latitudes and a great red spot (which is a storm). Jupiter is composed mostly of gas. This enormous planet radiates twice as much heat as it absorbs from the Sun. It also has an extremely strong magnetic field. Jupiter is so big that all the other planets in our Solar System could fit inside Jupiter (if it were hollow). Jupiter has four large moons and dozens of smaller ones (there are 39 moons known so far). More moons are being found all the time. This is the symbol of the planet Jupiter. Jupiter was named after the Roman primary god, Jupiter.

Saturn is the sixth planet from the sun in our solar system. It is the second-largest planet in our solar system (Jupiter is the largest). It has beautiful rings that are made mostly of ice chunks (and some rock) that range in size from the size of a fingernail to the size of a car. Saturn is made mostly of hydrogen and helium gas. Saturn is visible without using a telescope, but a low-power telescope is needed to see its rings. This is about 9.4 times the diameter of the Earth. Saturn has dozens of moons. It has 18 named moons including Titan (the largest), Rhea, Iapetus, Dione, Tethys, Enceladus, Mimas, Hyperion, Phoebe, Janus, Epimetheus, Pandora, Prometheus, Helene, Telesto, Atlas, Calypso, and Pan (the smallest named moon of Saturn). At least a dozen others have been noted (but not named yet). This is the symbol of the planet Saturn. Saturn was named for the Roman god of agriculture.

Uranus is the seventh planet from the sun in our solar system. This huge, icy planet is covered with clouds and is encircled by a belt of 11 rings and 22 known moons. Uranus’ blue color is caused by the methane in its atmosphere; this molecule absorbs red light. The mean temperature on the surface of Uranus’ cloud layer is -350°F (59 K). Uranus radiates very little heat in comparison with the other gas giants, Jupiter, Saturn and Neptune). Uranus has 5 large moons and many small moons (which were discovered later). This is the symbol of the planet Uranus. This planet was originally named in 1781 by the British astronomer William Herschel – he called it Georgium Sidus (meaning “the Georgian planet”) to honor the King George III of England. The name was later changed to Uranus, the ancient mythological god of the sky, Ouranos. The name Uranus was suggested by the German astronomer Johann Elert Bode.

Neptune is the eighth planet from the sun in our solar system. This giant, frigid planet has a hazy atmosphere and strong winds. This gas giant is orbited by eight moons and narrow, faint rings arranged in clumps. Neptune’s blue color is caused by the methane in its atmosphere; this molecule absorbs red light. Neptune cannot be seen using the eyes alone. This is 3.88 times the diameter of the Earth. If Neptune were hollow, it could hold almost 60 Earths. Neptune is the fourth largest planet in our Solar System (after Jupiter, Saturn, and Uranus). The mean temperature is 48 K. This is the symbol of the planet Neptune. Neptune was named after the mythical Roman god of the seas. Neptune’s symbol is the fishing spear.

Pluto is a dwarf planet (or plutoid) that usually orbits past the orbit of Neptune. It was classified as a dwarf planet in 2006; before that it was considered to be a planet, the smallest planet in our solar system. Pluto is smaller than a lot of the other planets’ moons, including our moon. Pluto is the only “planet” in our solar system that has not been visited by our spacecraft yet. Pluto is VERY, VERY cold. Pluto’s composition is unknown. Not much is known about Pluto’s atmosphere. It is probably mostly nitrogen with a little carbon monoxide and methane – definitely not breathable by humans. The atmospheric pressure is probably very low. From Pluto, the sky would seem black, even when the Sun (the size of a star) is up. Pluto has one large moon, named Charon; two minuscule moons Nix and Hydra. This is the symbol of Pluto. Pluto was named after the Roman god of the underworld, Pluto. Its symbol is the jointed letters “P” and “L,” either for Percival Lowell or for Pluto. The name Pluto was suggested by Venetia Burney of England, who was 11 years old then. She suggested the name to her grandfather, who was Librarian at Oxford. He passed her idea to the astronomers who were trying to name the newly discovered planet.