Planets in Solar system
Our solar system consists of an average star we call the Sun, the planets Mercury, Venus, Earth, Mars, Jupiter, Saturn, Uranus, Neptune, and Pluto. It includes: the satellites of the planets; numerous comets, asteroids, and meteoroids; and the interplanetary medium. The Sun is the richest source of electromagnetic energy (mostly in the form of heat and light) in the solar system. The Sun's nearest known stellar neighbor is a red dwarf star called Proxima Centauri, at a distance of 4.3 light years away. The whole solar system, together with the local stars visible on a clear night, orbits the center of our home galaxy, a spiral disk of 200 billion stars we call the Milky Way. The Milky Way has two small galaxies orbiting it nearby, which are visible from the southern hemisphere. They are called the Large Magellanic Cloud and the Small Magellanic Cloud. The nearest large galaxy is the Andromeda Galaxy
Sun
The Sun is the most prominent feature in our solar system. It is the largest object and contains approximately 98% of the total solar system mass. One hundred and nine Earths would be required to fit across the Sun's disk, and its interior could hold over 1.3 million Earths. The Sun's outer visible layer is called the photosphere and has a temperature of 6,000°C (11,000°F). This layer has a mottled appearance due to the turbulent eruptions of energy at the surface.
Solar energy is created deep within the core of the Sun. It is here that the temperature (15,000,000° C; 27,000,000° F) and pressure (340 billion times Earth's air pressure at sea level) is so intense that nuclear reactions take place. This reaction causes four protons or hydrogen nuclei to fuse together to form one alpha particle or helium nucleus. The alpha particle is about .7 percent less massive than the four protons. The difference in mass is expelled as energy and is carried to the surface of the Sun, through a process known as convection, where it is released as light and heat. Energy generated in the Sun's core takes a million years to reach its surface. Every second 700 million tons of hydrogen are converted into helium ashes. In the process 5 million tons of pure energy is released; therefore, as time goes on the Sun is becoming lighter.
Mercury
Mercury was named by the Romans after the fleet-footed messenger of the gods because it seemed to move more quickly than any other planet. It is the closest planet to the Sun, and second smallest planet in the solar system. Its diameter is 40% smaller than Earth and 40% larger than the Moon. It is even smaller than Jupiter's moon Ganymede and Saturn's moon Titan.
If an explorer were to step onto the surface of Mercury, he would discover a world resembling lunar terrain. Mercury's rolling, dust-covered hills have been eroded from the constant bombardment of meteorites. Fault-cliffs rise for several kilometers in height and extend for hundreds of kilometers. Craters dot the surface. The explorer would notice that the Sun appears two and a half times larger than on Earth; however, the sky is always black because Mercury has virtually no atmosphere to cause scattering of light. As the explorer gazes out into space, he might see two bright stars. One appearing as cream colored Venus and the other as blue colored Earth.
Venus
Venus, the jewel of the sky, was once know by ancient astronomers as the morning star and evening star. Early astronomers once thought Venus to be two separate bodies. Venus, which is named after the Roman goddess of love and beauty, is veiled by thick swirling cloud cover.
Earth
Many dream of traveling in space and viewing the wonders of the universe. In reality all of us are space travelers. Our spaceship is the planet Earth, traveling at the speed of 108,000 kilometers (67,000 miles) an hour.
Earth is the 3rd planet from the Sun at a distance of about 150 million kilometers (93.2 million miles). It takes 365.256 days for the Earth to travel around the Sun and 23.9345 hours for the Earth rotate a complete revolution. It has a diameter of 12,756 kilometers (7,973 miles), only a few hundred kilometers larger than that of Venus. Our atmosphere is composed of 78 percent nitrogen, 21 percent oxygen and 1 percent other constituents.
MarsMars is the fourth planet from the Sun and is commonly referred to as the Red Planet. The rocks, soil and sky have a red or pink hue. The distinct red color was observed by stargazers throughout history. It was given its name by the Romans in honor of their god of war. Other civilizations have had similar names. The ancient Egyptians named the planet Her Descher meaning the red one.
Jupiter is the fifth planet from the Sun and is the largest one in the solar system. If Jupiter were hollow, more than one thousand Earths could fit inside. It also contains more matter than all of the other planets combined. It has a mass of 1.9 x 1027 kg and is 142,800 kilometers (88,736 miles) across the equator. Jupiter possesses 28 known satellites, four of which - Callisto, Europa,
Saturn
Saturn is the sixth planet from the Sun and is the second largest in the solar system with an equatorial diameter of 119,300 kilometers (74,130 miles). Much of what is known about the planet is due to the Voyager explorations in 1980-81. Saturn is visibly flattened at the poles, a result of the very fast rotation of the planet on its axis. Its day is 10 hours, 39 minutes long, and it takes 29.5 Earth years to revolve about the Sun. The atmosphere is primarily composed of hydrogen with small amounts of helium and methane.
Uranus
Uranus is the seventh planet from the Sun and is the third largest in the solar system. It was discovered by William Herschel in 1781. It has an equatorial diameter of 51,800 kilometers (32,190 miles) and orbits the Sun once every 84.01 Earth years. It has a mean distance from the Sun of 2.87 billion kilometers (1.78 billion miles). It rotates about its axis once every 17 hours 14 minutes. Uranus has at least 22 moons. The two largest moons, Titania and Oberon, were discovered by William Herschel in 1787.
Pluto was discovered in 1930, limited information on the distant object delayed a realistic understanding of its characteristics. Pluto is the second largest known dwarf planet and tenth largest orbiting the Sun. From its time of discovery in 1930 to 2006 it was considered to be the ninth planet in the solar system, but because additional objects have been discovered including Eris which is 27% more massive, the IAU reclassified Pluto and the other objects as dwarf planets. The New Horizons spacecraft was launched on January 16, 2006 and will make its closest approach to Pluto on July 14, 1015. This mission will provide an increased amount of information about this peculiar dwarf planet. The uniqueness of Pluto's orbit, rotational relationship with its satellite, spin axis, and light variations all give it a certain appeal.
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