We live on one we call the Earth, which moves around a star we call the Sun. There are at least seven other planets moving around the Sun and a lot of other smaller things as well. All these things together are called a system. The Latin word for the Sun is Sol, so we call this system the Solar System.The Solar System. consists of the Sun together with the eight planets, their moons, and all other bodies that orbit it, including dwarf planets, asteroids, comets, meteoroids, and Kuiper belt objects. The outer limit of the solar system is formed by the heliopause. It is the same as the Heliosphere which is the bubble-like region that surrounds the Sun. Also, the sun made it.
There are likely to be many more planetary systems out there waiting to be discovered! Our Sun is just one of about 200 billion stars in our galaxy.
Main Planets
The English names for planets mostly come from the Romans, who borrowed their designations from gods and goddesses: Mercury was named for the messenger god because it appears to move so swiftly across the sky, Jupiter shares a title with the king of the gods because it’s the solar system’s giant, and so on
The order of the planets in the solar system, starting nearest the sun and working outward is the following: Mercury, Venus, Earth, Mars, Jupiter, Saturn, Uranus, Neptune, and then the possible Planet Nine. If you insist on including Pluto, it would come after Neptune on the list. 01
The planet Mercury looks a little bit like Earth’s moon. Like our Moon, Mercury’s surface is covered with craters caused by space rock impacts. Mercury is the closest planet to the sun and the eighth largest. … Mercury has a thick iron core and a thinner outer crust of rocky material.
Venus is bright white because it is covered with clouds that reflect and scatter sunlight. At the surface, the rocks are different shades of grey, like rocks on Earth, but the thick atmosphere filters the sunlight so that everything would look orange if you were standing on Venus.
Venus is the brightest object in the sky after the Sun and the Moon and sometimes looks like a bright star in the morning or evening sky. The planet is a little smaller than Earth and is similar to Earth inside. We can’t see the surface of Venus from Earth, because it is covered with thick clouds.
The Blue Marble is an image of Earth taken on December 7, 1972, from a distance of about 29,000 kilometers (18,000 miles) from the planet’s surface. It was taken by the crew of the Apollo 17 spacecraft on its way to the Moon and is one of the most reproduced images in history.
- The Earth’s rotation is gradually slowing. …
- The Earth was once believed to be the centre of the universe. …
- Earth has a powerful magnetic field. …
- There is only one natural satellite of the planet Earth. …
- Earth is the only planet not named after a god. …
- The Earth is the densest planet in the Solar System.
Mars is the fourth planet from the Sun and is the second smallest planet in the solar system. Named after the Roman god of war, Mars is also often described as the “Red Planet” due to its reddish appearance. Mars is a terrestrial planet with a thin atmosphere composed primarily of carbon dioxide.
Jupiter is called a gas giant planet. Its atmosphere is made up of mostly hydrogen gas and helium gas, like the sun. The planet is covered in thick red, brown, yellow, and white clouds. The clouds make the planet look like it has stripes. However, inside Jupiter, hydrogen can be a liquid or even a kind of metal. These changes happen because of the tremendous temperatures and pressures found at the core.
Jupiter is called a failed star because it is made of the same elements (hydrogen and helium) as is the Sun, but it is not massive enough to have the internal pressure and temperature necessary to cause hydrogen to fuse to helium, the energy source that powers the sun and most other stars.
As a gas giant, Jupiter doesn’t have a true surface. The planet is mostly swirling gases and liquids.
Saturn is the sixth planet from the Sun and the second-largest in the Solar System, after Jupiter. It is a gas giant with an average radius of about nine times that of Earth. It only has one-eighth the average density of Earth; however, with its larger volume, Saturn is over 95 times more massive.
- Saturn is the least dense planet in the Solar System. …
- Saturn is a flattened ball. …
Saturn spins so quickly on its axis that the planet flattens itself out into an oblate spheroid. Seriously, you see this by eye when you look at a picture of Saturn; it looks like someone squished the planet a little. Of course, it’s the rapid spinning that’s squishing it, causing the equator to bulge out.
- The first astronomers thought the rings were moons. …
- Saturn has only been visited 4 times by spacecraft. …
- Saturn has 62 moons.
- Saturn is the most distant planet that can be seen with the naked eye. …
- Saturn was known to the ancients, including the Babylonians and Far Eastern observers. …
- Saturn is the flattest planet. …
- Saturn orbits the Sun once every 29.4 Earth years. …
- Saturn’s upper atmosphere is divided into bands of clouds.
Uranus is the seventh planet from the Sun. It has the third-largest planetary radius and fourth-largest planetary mass in the Solar System. Uranus is similar in composition to Neptune, and both have bulk chemical compositions that differ from that of the larger gas giants Jupiter and Saturn.
Uranus’ atmosphere is similar to Jupiter’s and Saturn’s in its primary composition of hydrogen and helium, but it contains more “ices” such as water, ammonia, and methane, along with traces of other hydrocarbons. It has the coldest planetary atmosphere in the Solar System, with a minimum temperature of 49 K (−224 °C; −371 °F), and has a complex, layered cloud structure with water thought to make up the lowest clouds and methane the uppermost layer of clouds. The interior of Uranus is mainly composed of ices and rock.
Uranus has a ring system, a magnetosphere, and numerous moons. The Uranian system has a unique configuration because its axis of rotation is tilted sideways, nearly into the plane of its solar orbit. Its north and south poles, therefore, lie where most other planets have their equators. In 1986, images from Voyager 2 showed Uranus as an almost featureless planet in visible light, without the cloud bands or storms associated with the other giant planets. Voyager 2 remains the only spacecraft to visit the planet. Observations from Earth have shown seasonal change and increased weather activity as Uranus approached its equinox in 2007. Wind speeds can reach 250 meters per second (900 km/h; 560 mph).
Neptune is the eighth and farthest known planet from the Sun in the Solar System. In the Solar System, it is the fourth-largest planet by diameter, the third-most-massive planet, and the densest giant planet. Neptune is 17 times the mass of Earth, slightly more massive than its near-twin Uranus. It is an ice giant but similar to a gas giant. It is made of a thick soup of water, ammonia, and methane flowing over a solid core about the size of Earth. Due to its blue coloration, Neptune was named after the Roman god of the Sea. Neptune, like the other gas giants in our solar system, doesn’t have much of a solid surface to live on.- Neptune is the most distant planet from the Sun.
- Neptune is the smallest gas giant.
- A year on Neptune lasts 165 Earth years.
- Neptune is named after the Roman god of the sea.
- Neptune has 6 faint rings.
- Neptune’s largest natural moon [satellite] is Triton. It consists of a crust of frozen nitrogen over an icy mantle believed to cover a core of rock and metal. Triton has a density of about twice that of water.
Dwarf planets
A “dwarf planet” is a celestial body that (a) is in orbit around the Sun, (b) has sufficient mass for its self-gravity to overcome rigid body forces so that it assumes a hydrostatic equilibrium (nearly round) shape,2 (c) has not cleared the neighborhood around its orbit, and (d) is not a satellite. In order words, it does not dominate its region of space and is not a satellite.
The only difference between a planet and a dwarf planet is the area surrounding each celestial body. A dwarf planet has not cleared the area around its orbit, while a planet has. Since the new definition, three objects in our solar system have been classified or re-classified as dwarf planets: Pluto, Ceres, and Eris.
There are 5 officially recognized dwarf planets in our solar system, they are Ceres, Pluto, Haumea, Makemake, and Eris.
Ceres is the largest object in the main asteroid belt that lies between the orbits of Mars and Jupiter. With a diameter of 940 km, Ceres is both the largest of the asteroids and the only unambiguous dwarf planet currently inside Neptune’s orbit.
Most of the surface is a dull gray. Spectral observations from Ceres have revealed the presence of a form of graphite known as graphitized carbon. “It hasn’t evolved to proper graphite,” Amanda Hendrix, a senior scientist at the Planetary Science Institute in Arizona, told Space.com. But it’s close. Ceres has a tenuous water vapor atmosphere outgassing from water ice on the surface, making it an active asteroid, and can hit the earth. About 30 small asteroids a few meters in size hit Earth every year. They make spectacular fireballs in the atmosphere, and sometimes fragments make it to the surface as meteorites but don’t cause any significant damage on the ground. –
Ceres is not a planet because it does not dominate its orbit, sharing it as it does with the thousands of other asteroids in the asteroid belt and constituting only about 25% of the belt’s total mass. Ceres takes 1,682 Earth days, or 4.6 Earth years, to make one trip around the sun. As Ceres orbits the sun, it completes one rotation every 9 hours, making its day length one of the shortest in the solar system.
Pluto is thought to be made of mostly ice and is the brightest object in the Kuiper Belt. It probably also has a small rocky core which might contain some metals. The ice on the surface of Pluto is made of frozen nitrogen, methane, and carbon monoxide. The planet has a range of colors, including pale sections of off-white and light blue, to streaks of yellow and subtle orange, to large patches of deep red; but it is mostly brown.
Haumea resides in the Kuiper belt and is roughly the same size as Pluto. Haumea is one of the fastest rotating large objects in our solar system. Its fast spin distorts Haumea’s shape, making this dwarf planet look like a football. It has the shortest day of all the dwarf planets, only 3.9 hours.
Makemake is a dwarf planet in the outer solar system. It was the fourth body identified as a dwarf planet and was one of the bodies that caused Pluto to lose its status as a planet. Makemake is large enough and bright enough to be studied by a high-end amateur telescope, it does appear to be a reddish-brownish color and orbits at 45.3 times Earth’s distance and takes more than 305 years to complete a circuit of the sun. Its day is 22.5 hours and the average diameter is 882 miles (1,420 km).
Originally designated 2003 UB313 (and nicknamed for the television warrior Xena by its discovery team), Eris is named for the ancient Greek goddess of discord and strife. The name fits since Eris remains at the center of a scientific debate about the definition of a planet.- Its apparent magnitude of 18.7 makes it bright enough to be detected by amateur telescopes.
- It doesn’t have rings, nothing is known about its magnetosphere but it does have a moon named Dysnomia after the demon goddess of lawlessness and the daughter of Eris.
- It takes about 558 Earth years for Eris to make one trip around the Sun. As it orbits the Sun, it completes one rotation every 25.9 hours.
- The plane of Eris’s orbit is well out of the plane of the Solar System’s planets and extends far beyond the Kuiper Belt thus beyond the orbit of Neptune, located in a region called the scattered disk.
- Like Pluto, it’s a little smaller than Earth’s moon. It has a radius of about 722 miles or 1,163 kilometers, thus 1/5 the radius of Earth.
Galaxies
A galaxy is a huge collection of gas, dust, and billions of stars and their solar systems. A galaxy is held together by gravity. Our galaxy, the Milky Way, also has a supermassive black hole in the middle.
They’ve been described as “island universes” and come in many sizes and shapes: elliptical, spiral, barred spiral, and irregular.
Elliptical Galaxies
Elliptical galaxies have an elongated spherical shape and lack a nucleus or bulge at the center. Although there is no nucleus, the galaxy is still brighter in the center and becomes less bright toward the outer edges of the galaxy.
Elliptical galaxies have very little activity and contain mostly old stars of low mass, because there gasses and dust which is needed to form new stars, is quite lacking.
Spiral Galaxies
They have a flat, spinning disk with a central bulge surrounded by spiral arms. The spinning motion reaches speeds of up to hundreds of kilometers/miles per second. This usually can cause matter in the disk to take on a distinctive spiral shape, like a cosmic pinwheel. The bulge located in the center is made up of older, dimmer stars, and is thought to usually contain a supermassive black hole.
Barred Spiral Galaxies
Barred spiral galaxies share the same features and functions as regular spiral galaxies, but they also have a bar of bright stars that lie along the center of the bulge and extend into the disk. The bright bulge has very little activity here and contains mostly older, red stars. The bar and arms have lots of activity, including star formation. The most famous is the Milky Way. 
Irregular Galaxies
Irregular galaxies have no definite shape, though they are in constant motion like all other galaxies. They have a chaotic appearance as they don’t seem to possess a nuclear bulge or traces of spiral arms.
Some irregular galaxies were once spiral or elliptical galaxies but were deformed by an uneven external gravitational force. Irregular galaxies may contain abundant amounts of gas and dust Irregular galaxies are commonly small, about one-tenth the mass of the Milky Way galaxy whose gravitational force distorts the clouds of its neighbors.
Other types of Galaxies
Some galaxies have a ring-like structure of stars and interstellar medium surrounding a bare core. It is believed that they take this shape when smaller galaxies pass through the core of spiral galaxies.
On the other end, there are starburst galaxies that are characterized by dusty concentrations of gas and the appearance of newly formed stars. Usually, many of these stars are massive and result in supernova explosions that interact powerfully with the surrounding gas.
Celestrial Belts
This image depicts the two areas where most of the asteroids in the Solar System are found: the asteroid belt between Mars and Jupiter, and the trojans, two groups of asteroids moving ahead of and following Jupiter in its orbit around the Sun.
Kuiper BeltThe Kuiper Belt is a doughnut-shaped ring of icy objects around the Sun, extending just beyond the orbit of Neptune. Occasionally called the Edgeworth–Kuiper belt, it is a circumstellar disc in the outer Solar System, extending from the orbit of Neptune to approximately 50 AU from the Sun. It is similar to the asteroid belt, but is far larger—20 times as wide and 20 to 200 times as massive.
Lots of Kuiper Belt objects have moons—that is, significantly smaller bodies that orbit them—or are binary objects. It’s one of the places where comets come from. Pluto was the first Kuiper Belt object to be discovered, in 1930, at a time before astronomers had reason to expect a large population of icy worlds beyond Neptune.
Glossary
Terrestrial planets – The four innermost planets of our solar system (Mercury, Venus, Earth, and Mars) are called the “terrestrial” planets. The name comes from the word “telluric” derived from the Latin words “terra” and “tellus”, used to refer to Earth. They are made mostly of silicate rocks and metals, with solid surfaces and atmospheres that range from thick (on Venus) to very thin (on Mercury). Earth is the only one with liquid oceans, although Mars may have had them in the past.
a magnetosphere is a region of space surrounding an astronomical object in which charged particles are affected by that object’s magnetic field. It is created by a star or planet with an active interior dynamo.
asteroids are made of rock, metals, and other elements. Some even contain water, astronomers say. Asteroids that are mostly stone sometimes are more like loose piles of rubble. Asteroids that are mostly iron are more, well, rock-solid.
AU means an astronomical unit. It is a simplified number used to describe a planet’s distance from the sun. It is a unit of length equal to the average distance from Earth to the sun, approximately 149,600,000 kilometers (92,957,000 miles). Only Earth can be assigned AU 1.
Sources: Space.com, nasa.gov, Space-facts.com, Wikipedia, THE NINE PLANETS