Galaxy, Solar System and Planets


Galaxy, Milky Way, Stars, Solar System, Asteroids, Sun, Comet, Natural Satellite, Moon
Nine planets: Mercury, Venus, Earth, Mars, Jupiter, Saturn, Uranus, Neptune and Pluto


Galaxy: Hundreds of millions of stars, all gravitationally interacting, and orbiting about a common center. Astronomers estimate that there are about 125 billion galaxies in the universe. All the stars visible from the Earth belong to Earth’s galaxy called the Milky Way. The Sun, with its associated planets, is just one star in this galaxy. Besides stars and planets, galaxies contain clusters of stars; atomic hydrogen gas; molecular hydrogen; complex molecules composed of hydrogen, nitrogen, carbon, and silicon, among others and cosmic rays.
Milky Way: the large, disk-shaped aggregation of stars, or galaxy, that includes the Sun and its solar system. In addition to the Sun, the Milky Way contains about 400 billion other stars. There are hundreds of billions of other galaxies in the universe, some of which are much larger and contain many more stars than the Milky Way.
Stars: Massive shining sphere of hot gas. Of all the stars in the Universe, our Sun is the nearest to Earth and the most extensively studied. The stars visible from the earth all belong to the Milky Way Galaxy, the massive ensemble of stars that contains our solar system (the Sun and it’s nine planets).
Solar System: The Sun and the celestial bodies orbiting the Sun. Including the nine planets and their satellites; the asteroids and comets; and interplanetary dust and gas. Here the solar system refers to the system that includes Earth and the Sun.  
Asteroids: one of the many small or minor rocky planetoids that are members of the solar system and that move in elliptical orbits primarily between the orbits of Mars and Jupiter.

Sun: closest star to Earth. The Sun is a huge mass of hot, glowing gas. The strong gravitational pull of the Sun holds Earth and the other planets in the Solar System in orbit. The Sun’s light and heat influence all of the objects in the solar system and allow life to exist on Earth. Sun light is a combination of seven colors called rainbow.

Comet: relatively small, icy celestial body revolving around the Sun. When a comet nears the Sun, some of the ice in the comet turns into gas. The gas and loose dust freed from the ice create a long, luminous tail that streams behind the comet.
Natural Satellite: in astronomy, a celestial body that orbits a larger celestial body. The larger body is referred to as the satellite’s primary. Natural satellites that orbit planets are often called moons.
The best-known natural satellite is Earth's Moon. The Moon is unusually large relative to the size of its primary (Earth); in fact, it is significantly larger than the planet Pluto. The Moon’s surface, like the surfaces of most of the natural satellites in the solar system, is heavily cratered and geologically inactive.
Moon: Name given to the only natural satellite of Earth. The Moon is the second brightest object in Earth’s sky, after the Sun, and has accordingly been an object of wonder and speculation for people since earliest times. The natural satellites of the other planets in the solar system are also sometimes referred to as moons  
Nine planets: Mercury, Venus, Earth, Mars, Jupiter, Saturn, Uranus, Neptune and Pluto.
Mercury: Orbits closest to the Sun.  

Venus: The second in distance from the Sun.  

Earth: The only planet known has a life, and the “home” of human beings. From space Earth resembles a big blue marble with swirling white clouds floating above blue oceans. About 71 percent of Earth’s surface is covered with water, which is essential to life. The rest is land, mostly in the form of continents that rise above the oceans.  

Mars: It is the fourth planet from the Sun.  

Jupiter: Fifth planet from the Sun and the largest planet in the solar System.  

Saturn: Sixth planet in order of distance from the Sun, and the second largest in the Solar System.  

Uranus: Major planet in the solar system, seventh planet from the Sun. Uranus revolves outside the orbit of Saturn and inside the orbit of Neptune.  

Neptune: It is an eight planet from the Sun and fourth largest in diameter.  

Pluto: Ninth planet from the Sun and outermost known planet of the Solar System.  

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