Mercury, Venus, Earth, Mars, Jupiter, Saturn, Uranus, and Neptune are the eight planets. Mercury is the nearest planet to the Sun. Neptune is the farthest away. Our Sun is orbited by planets, asteroids, and comets. These objects either orbit around the Sun or lie in its general path, but none lies exactly opposite it like Earth does.
The names of the planets were first given to the objects themselves. They were called "planets" because they seemed to wander across the sky back in ancient times. Today we know them as the Sun's companions because they're only visible in the sunlight. They don't reflect light like Earth does so they can't be seen at night.
However, over time people have found other ways to identify these bodies even though they aren't always able to see them directly. For example, astronomers know about Mars' canals by looking at their images from satellites and spacecraft. They think this may be where Mars' water comes out from beneath the surface.
Scientists also use data from planetary studies to learn more about our own Solar System and beyond. For example, scientists have used information about Jupiter's moons to help them understand how galaxies form planets.
Finally, astronomers use predictions from theories about the future course of the solar system to guide them when they look through telescopes.
The solar system has eight planets. Mercury, Venus, Earth, Mars, Jupiter, Saturn, Uranus, and Neptune are the planets nearest to the Sun and furthest away. Terrestrial planets are the first four planets discovered. They are primarily solid and built of rock and metal. The other four are gas giants with large quantities of hydrogen and helium trapped in their cores.
The term planet comes from the Greek word for wanderer, because astronomers used to think that these bodies moved across the sky. But they don't move far enough to leave their orbits around the Sun. Instead, each planet travels along its orbit within the Solar System when viewed from outside it. For example, when viewing the Solar System from afar on a clear night, every six months or so you would see Mars go behind Earth before reappearing.
Today, we know better than to call them planets anymore. They are referred to as terrestrial worlds, super-earth, iron core, silicon shell, or gas giant, depending on which one is being discussed.
The terms planet and world are used interchangeably today but they weren't always connected. Before telescopes revealed much about other worlds beyond our own, people thought that planets were only stars that appeared bright in daylight because they had moons orbiting them.
The Planets' Size and Order Mercury, Venus, Earth, Mars, Jupiter, Saturn, Uranus, and ultimately Neptune are listed in order of proximity to the Sun. Jupiter is the biggest planet in the solar system. It is followed by Saturn, Uranus, Neptune, Earth, Venus, and Mars, with Mercury being the smallest.
The distances between the planets vary greatly. The nearest planet is Mercury, which orbits the Sun every 88 days. The most distant planet is Neptune, which takes about 25 years to orbit the Sun. Between them lie Earth, Venus, Mars.
All the planets but one are classified as terrestrial planets, meaning that they are not composed entirely of gas like the giant planets Jupiter and Saturn. Instead, they are dominated by rocks and metals. The exception is Neptune, which is mostly hydrogen instead.
Terrestrial planets tend to be more circular than celestial bodies such as the Moon or Venus because they do not suffer tidal forces like those experienced by satellites. However, some astronomers include Pluto in this category because it has a dense atmosphere made of nitrogen and methane molecules that is very similar to our own.
The eight terrestrial planets are all rocky, with the exception of Neptune which is mainly hydrogen. However, the four largest planets (Jupiter, Saturn, Uranus, and Neptune) have large quantities of gas inside them which produce a gravitational pull on themselves and their surroundings. This is called "gravitational force".
Our solar system consists of a star, the Sun, eight planets, 146 moons, a slew of comets, asteroids, space rocks, ice, and numerous dwarf planets, including Pluto. As far as we can tell, none of the planets move around their stars. Instead, they orbit around the center of our Milky Way Galaxy.
The order of the planets from closest to sun to farthest from sun is: Mercury, Venus, Earth, Mars, Jupiter, Saturn, Uranus, Neptune. This order follows distance from Earth's surface to location where each planet can be found on the horizon at its closest approach to Earth during its yearly orbit around the Sun. The only exception is Mercury, which because it is so small, it can never be seen directly but always appears in the night sky as a dim red dot against the bright background of the Sun's glare. From this location beyond Earth's atmosphere, they each take approximately six months to return to their closest approach to the Sun before moving off into darkness again.
These are the only eight planets that have been discovered thus far, but there may be others undiscovered yet. Scientists think that there could be billions of planets in our galaxy alone, so it is likely that there are many more worlds beyond our own Solar System.
Mercury, Venus, Earth, Mars, Jupiter, Saturn, Uranus, and Neptune are listed in order of distance from the sun. Pluto, which was previously thought to be the furthest planet, is now categorized as a dwarf planet.