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Read some really neat facts about the planets in our solar system!
© Contributed by Leanne Guenther
Note: The fast facts on this page are appropriate for grades 1 to 3 while the "more about" links are appropriate for grades 4+.
I've listed them in order from closest to furthest from the sun:
- Ceres (dwarf planet found in the asteroid belt)
- Pluto (Note: Pluto is considered a dwarf planet now)
- Eris, Makemake, Haumea, Sedna (also dwarf planets -- found past Pluto)
Mercury takes 59 days to make a rotation but only 88 days to circle the Sun. That means that there are fewer than 2 days in a year!
Many astronomers believe that Mercury might be the core of what was once a much larger planet -- it appears to be a huge ball of iron covered by a thin layer of rock.
Venus is the brightest planet in our sky and can sometimes be seen with the naked eye if you know where to look. It is the solar system's brightest planet -- yellow clouds of sulfuric acid reflect the sun's light.
Earth has more exposed water than land. Three quarters of the Earth is covered by water! The earth has one moon.
On-Line Jigsaw Puzzles:
Mars is the home of "Olympus Mons", the largest volcano found in the solar system. It stands about 27 kilometers high with a crater 81 kilometers wide.
Between Mars and Jupiter, is a Dwarf Planet known as Ceres. It was discovered in 1801. It is the smallest dwarf planet discovered in our universe (so far) and is the only one found in the asteroid belt. A dwarf planet is NOT a planet -- the solar system is made up of:
- a star (the sun),
- planets (ex: jupiter and earth),
- satellites (ex: the moon),
- dwarf planets (ex: Ceres and Pluto), and
- small solar system bodies (ex: asteroids and comets).
Jupiter is the largest planet in the solar system, but it spins very quickly on its axis. A day on Jupiter lasts only 9 hours and 55 minutes. Ack, I get dizzy just thinking about it!
Jupiter is so big that you could fit all the other planets in the solar system inside it.
The red spot of Jupiter is the biggest, most violent storm in the known universe -- that spot is at least three times the size of earth!
more about Jupiter >
(including actual photos)
Saturn is the second biggest planet, but it’s also the lightest planet. If there was a bathtub big enough to hold Saturn, it would float in the water!
The rings that surrounds Saturn could be the remnants of a moon that was shattered by Saturn's gravity. Saturn's rings are as wide as 22 planet earths all in a row but are only 30 feet thick!
more about Saturn >
(including actual photos)
Uranus’ axis is at a 97 degree angle, meaning that it orbits lying on its side! Talk about a lazy planet.
Uranus has the second most complex set of rings in our solar system (Saturn has the most defined rings).
Neptune was discovered in 1846. In 2011 it finally made it's first lap around the sun since we discovered it -- because one Neptune year lasts 165 Earth years!
Like Jupiter, Neptune has a dark spot caused by a storm. Neptune's spot is smaller than Jupiter's -- it is only about the size of the planet earth.
Pluto’s orbit sometimes brings it closer to the Sun than Neptune. It jumped ahead of Neptune on September 5, 1989 and remained there until February, 1999 when it went back to being the farthest.
Note: Pluto is no longer considered a planet -- instead, astronomers call it a dwarf planet or planetoid. Whatever the name, our solar system isn't the neat model we once thought it was. It takes a bit for grown-ups (like me!) to adapt to the changes in our understanding (I now understand a bit better how folks felt when someone started telling them the earth was round not flat!)
On July 14, 2015, the NASA space probe "New Horizons" finally made it to Pluto after its 9.5 year journey. It took lots of cool photos of Pluto and its moons and sent them back to us on Earth. Then it continued off into space -- who knows where it will end up!
To me, Pluto just keeps getting more awesome despite it losing its place as one of our planets (when I was young, it was my favorite). I love that thanks to projects like New Horizons, we now know that Pluto has a cute little heart shaped area on it. Yep... Pluto has a heart!
In January 2005, astronomers in the United States discovered a new body orbiting the sun in our solar system. They named this planetoid, Eris after the Greek goddess of strife.
Eris takes approximately 550 earth years to orbit the sun. The majority of the time, it is further from the sun than Pluto, but for a short time, it is closer.
Eris is actually larger than Pluto (it is the ninth largest object orbitting our sun discovered so far!)
Makemake and Haumea are dwarf planets just like Pluto, but a little further out in our solar system. Because their orbits are not perfect circles, they trade places in terms of which is closer and which is further from the sun.
Both were discovered in late 2004/early 2005.
Haumea has a squished egg shape -- thought to be the result of a collision from an asteroid or meteor at some time.
In 2004, astronomers in universities in the United States discovered a new body orbiting the sun in our solar system. They named this planetoid, Sedna after the Inuit goddess of the Ocean. This is the furthest orbiting body identified in our solar system to date.
Sedna is about three times further from our sun than Pluto. It takes between 10,500 and 12,000 earth years for Sedna to make one orbit around the sun (we haven't quite figured out exactly how long it takes).
the most beautiful craft I've ever seen!
Definition of a 'Planet': What makes something 'beautiful'? Is a Picasso painting beautiful? Or do you prefer a photograph? Or perhaps the first frog paper craft ever created by a beloved three year old is where beauty lies for you.
Definitions are created by people to describe the universe that surrounds us. But we don't have a 'King of Definitions' to tell us when we've got it right! Sometimes we all agree on what something means and sometimes we don't.
There is no 'King of Definitions' in charge of deciding what is a planet and what is not. These decisions are the result of a lot of thinking and conversation by a lot of very smart people. And these decisions change over time as our knowledge grows and changes.
Where we stand now, there are 8 'planets' in our solar system and a number of planetoids (dwarf planets). The biggest deciding factor that makes something a planet is that it orbits on the same plane, that it has significant gravity and that it is a large enough size.
It will be interesting to see how our solar system shapes up as astronomers discover more and more through technologies such as the Hubble Telescope!
Note: This section last updated in July 2015. Our understanding of our solar system is always being updated due to new technologies and new discoveries!
Essay on Our Universe: Definition, Stars and Solar System!
When we look at the sky, we see different kinds of natural bodies like the sun, the stars, the moon, and so on. The natural bodies in the sky are called celestial bodies or heavenly bodies. They are part of our universe. The universe is a huge space which contains everything that exists. The celestial bodies that we see are just a small fraction of the bodies that exist in the universe. One of the reasons why we do not see more of them is that they are very, very far away.
To measure the large distances in the universe, scientists use a unit of length called the light year. A light year is the distance travelled by light in one year. Light travels 9.46 trillion km in a year (one trillion is 1 followed by 12 zeroes).
One light year represents this huge distance. Proxima Centauri, the star closest to our solar system, is 4.2 light years from us. This means that light from this star takes 4.2 years to reach us. In this article, we shall learn a bit about stars and our solar system. But before that, let us see how the universe was formed.
Scientists believe that the universe was born after a massive explosion called the ‘big bang’. A long time after the big bang, stars like our sun were formed. At that time, clouds of hot gases and particles revolved around the sun. Over time, many particles got stuck together to form large bodies. These bodies pulled in smaller objects near them by gravitational force. This made them larger still. These bodies finally became the planets.
Away from the lights of the city, you can see thousands of stars in the night sky. You can also see some planets and their moons, either with the naked eye or with the help of a telescope. These celestial bodies are different from the stars in one important way. Stars are celestial bodies that produce their own heat and light. Planets and their moons shine by reflecting the light of a star such as our sun.
All stars are huge balls of hydrogen and helium gases. In a star, hydrogen gets converted into helium. In this reaction, a large amount of energy is liberated. This is the source of the heat and light of a star. Stars vary in brightness and size. Some are medium-sized, like our sun. Some are so huge that if they were to be placed in our sun’s position, they would fill the entire solar system!
There are trillions of stars in the universe. They occur in groups called galaxies. The gravitational force between stars keeps the stars of a galaxy together. Apart from stars, a galaxy may have other celestial bodies like planets and moons. So you can say that a galaxy is a group of stars and other celestial bodies bound together by gravitational force.
The distribution of the stars in a galaxy can give it a shape such as spiral, ring or elliptical. Our sun is a part of a spiral galaxy called the Milky Way Galaxy. This galaxy is named after the Milky Way. The Milky Way is a band of stars that we can see on a clear night. These stars are a part of our galaxy. The ancient Romans called this band of stars Via Galactica, or ‘road of milk’. That is how our galaxy got its name.
As the earth moves round the sun, we see different stars at different times of the year. In the past, people found many uses for this. For example, they would get ready for sowing when particular stars appeared in the sky. Obviously, it was not possible for them to identify each and every star. So, they looked for groups of stars which seem to form patterns in the sky. A group of stars which seem to form a pattern is called a constellation.
Ancient stargazers made stories about the constellations and named them after the animals, heroes, etc., from these stories. So constellations got names like Cygnus (swan), Leo (lion), Taurus (bull), Cancer (crab), Perseus (a hero) and Libra (scale). You can see many of these constellations on a clear night.
The Great Bear (Ursa Major) is one of the easiest constellations to spot. You can see it between February and May. Its seven brightest stars form the shape of a dipper (a long-handled spoon used for drawing out water). Together, these stars are called the Big Dipper or Saptarshi. These and the other stars of the constellation roughly form the shape of a bear.
The two brightest stars of the Big Dipper are called ‘pointers’ because they point towards the pole star. The pole star lies at the tail of the bear of a smaller constellation called the Little Bear (Ursa Minor).
To find the north direction, ancient travellers would look for the Big Dipper and from there, locate the pole star. While all stars seem to move from the east to the west (as the earth rotates in the opposite direction), the pole star seems fixed. This is because it lies almost directly above the earth’s North Pole [Figure 13.3 (c)].
Orion (the Hunter) and Scorpius are two other prominent constellations. There are different stories linking them. According to one, the mighty hunter Orion vowed to kill all the animals of the world. Alarmed at this, the Earth Goddess sent a scorpion to kill Orion. He ran away, and continues to do so even now. This story takes into account the fact that Orion goes below the horizon when Scorpius rises. Orion rises again only when Scorpius sets.
Remember that constellations are imaginary. For our convenience we have picked a few stars that resemble a pattern and called them a constellation. On the other hand, galaxies are real things in which stars and other celestial bodies are held together by gravitational force.
The Solar System:
The sun is the brightest object in the sky. It is huge. It is about 333,000 times heavier than the earth, and you could fit more than a million earths inside it! Its great mass causes a large gravitational force. This keeps the sun, the planets, their moons and some other smaller bodies together as the sun’s family. The sun and all the bodies moving around it are together called the solar system. All the members of the solar system revolve around the sun in almost circular paths, or orbits.
After the sun, the planets are the largest bodies in our solar system. Scientists define a planet as a round body that orbits the sun and which has pulled in all objects near its orbit. Remember that planets were formed when large bodies in space pulled in smaller bodies near it. This cleared the space around a planet’s orbit.
There are eight planets in our solar system. In order of distance from the sun they are Mercury, Venus, Earth, Mars, Jupiter, Saturn, Uranus and Neptune. You can remember this order as My Very Efficient Maid Just Served Us Noodles.
Apart from revolving around the sun, each planet rotates, or spins, about its axis. The time taken to complete a revolution around the sun is the length of a planet’s year. And the time taken to complete one rotation is the planet’s day.
The four planets closest to the sun—Mercury, Venus, Earth and Mars—are small, rocky planets. They are called terrestrial (earthlike) planets. The other four planets—Jupiter, Saturn, Uranus and Neptune—are giants in comparison.
They are made up mainly of gases. They are called gas giants or Jovian (Jupiter like) planets. All the gas giants have rings around them. Since they are very far from the sun, the gas giants are much colder than the terrestrial planets.
While stars twinkle, planets shine with a steady light. You can see some of the planets with the naked eyes or with the help of a good pair of binoculars. Just remember that as the planets move around the sun, they appear at different positions in the sky at different times of the year. And for the period they are behind the sun, they are not visible.
Mercury, the smallest planet of our solar system, revolves around the sun the fastest. But it rotates on its axis at a much slower speed than the earth. So, a day on Mercury is about 58 times longer than a day on earth.
Although Mercury is the closest to the sun, it is not the hottest planet. Its thin atmosphere cannot trap heat. So, at night, when there is no sun, the temperature can fall to as low as -180°C. You can see Mercury near the eastern horizon before sunrise at certain times of the year. And at certain other times, you can see it near the western horizon after sunset.
The thick atmosphere of Venus makes it the brightest and the hottest planet of the solar system. Its atmosphere has mainly carbon dioxide gas, which reflects a lot of sunlight. But it also traps so much heat that the average temperature on Venus is about 450°C.
Venus takes 243 days to complete one rotation, making its day the longest in the solar system. As a matter of fact, a day on Venus is longer than its year! It is easy to spot Venus because it is so bright. When it is visible in the east before sunrise, it is called a morning star. And when it is visible in the west in the evening, it is called an evening star.
The earth is not the fastest, slowest, hottest, coldest, largest or smallest planet. But it is the only planet on which life is known to exist. The planet’s distance from the sun, the composition of its atmosphere and the fact that liquid water is found on it make life possible on it.
Were it nearer the sun, the water on it would have evaporated. Were it farther away, all our oceans, rivers and lakes would have frozen. The carbon dioxide in the earth’s atmosphere plays two important roles. Plants use it to make food—which feeds, directly or indirectly, all animals. It also traps just enough heat to ensure that the nights on earth do not become freezing cold.
No other planet evokes so much interest as Mars does. This is because scientists have found evidence that liquid water once flowed through the channels visible on its surface. So it is possible that some form of life once existed on this planet. The rust-coloured soil of Mars gives it a red colour. So, it is also called the Red Planet.
When visible, Mars looks like a red sphere. During its two-year orbit, it looks the brightest when the earth is between the sun and Mars. During this time, you can see it rise in the east as the sun sets in the west.
Jupiter is the largest and the heaviest planet of our solar system. It also has the largest number of moons. The strong winds blowing on it, and on the other gas giants, create light and dark areas, giving them a striped look.
If you look through a powerful telescope, you will see a big spot on Jupiter’s surface. This spot is actually a huge storm, which has been raging on Jupiter for more than 300 years. In 1979, the Voyager 1 spacecraft discovered faint rings around Jupiter. These rings are not visible even through the most powerful earth-based telescopes. Jupiter is also visible to the naked eye. It looks like a bright spot in the sky.
You can easily recognise a picture of Saturn because of the planet’s prominent rings. These rings are actually particles of dust and ice revolving around Saturn. Apart from these particles, a large number of moons orbit this planet.
Uranus and Neptune:
Uranus and Neptune are the third and the fourth largest planets respectively. Yet, they were the last two planets to be discovered. That is because they are so far away from us. Even today, we know very little about them.
The moons of planets:
An object revolving around a celestial body is known as a satellite. All planets except Mercury and Venus have natural satellites, or moons, revolving around them. So far, we know of more than 150 planetary moons. Some of them are so small that they were discovered only when spacecraft flew past them. A few of the moons are almost as large as planets. One of Jupiter’s moons, Ganymede, is the largest of them all. It is even larger than Mercury. Of all the moons, we know the most about the earth’s moon.
The earth’s moon:
The earth’s moon is the brightest object in the night sky. It shines by reflecting sunlight. If you look at the moon through a telescope or a good pair of binoculars, you will see a number of craters on its surface. These are large depressions created when huge rocks from space hit the moon. The moon does not have water or an atmosphere. It also does not have life on it.
The moon takes 27 days and 8 hours to complete one revolution around the earth. In this time it also completes one rotation around its axis. We see different shapes of the moon as it travels around the earth.
Stand in front of a lamp in a darkened room. Hold a ball in your outstretched arm and move it around you, just as the moon moves around the earth. A friend standing some distance away from you will always see half of the ball (moon) lit by the lamp (sun). But to you (earth) the shape of the lit portion will keep on changing, like the changing shapes of the moon.
Sunlight lights up half of the moon. As the moon revolves around the earth, we see different parts of the sunlit half. The shapes of these parts are called the phases of the moon. When the entire side facing the earth is sunlit, the moon appears as a full disc. We call this the full moon or purnima. And when the side of the moon facing us gets no sunlight, we do not see the moon.
This is called the new moon or amavasya. After the new moon, the moon appears as a thin crescent. As days pass, we see larger portions of the moon till the full moon appears. After this, the size of the moon visible to us gradually decreases till we once again have the new moon. The whole cycle of one new moon to the next takes 29.5 days. So the new moon and the full moon appear about fifteen days from each other.
A dwarf planet is a small, round body that orbits the sun. At the time of its formation, a dwarf planet could not pull in all other objects near its orbit. So it is not considered a planet. Pluto, which was previously considered a planet, is now considered a dwarf planet. Ceres and Eris are two other dwarf planets.
In a belt between the orbits of Mars and Jupiter, millions of small, irregular, rocky bodies revolve around the sun. These are asteroids, and the belt is known as the asteroid belt. Asteroids are also called minor planets.
Scientists think that asteroids are pieces of material that failed to come together to form a planet when the solar system was being formed. Asteroids can measure a few metres to hundreds of kilometres in width. Some asteroids even have moons.
Asteroids were not the only pieces of rock left over from the formation of the solar system. Some others, called meteoroids, still orbit the sun. When they come very close to a planet such as the earth, gravitation pulls them in.
As they enter the earth’s atmosphere, they heat up because of friction with the air, and start burning. As these burning meteoroids fall towards the ground, we see them as streaks of light. The streak of light caused by a burning meteoroid is called a meteor or a shooting star.
Fortunately, the material of most meteoroids burns up completely before it can reach the surface of the earth. However, some large ones fail to burn up completely and strike the earth’s surface. Meteoroids that fall on a planet or a moon are called meteorites. A large meteorite can create a large crater and cause a lot of damage.
Scientists think that dinosaurs were wiped off the earth following a meteorite hit. Meteorite hits are more common on those planets and moons which have little or no atmosphere to burn off the falling rock. The craters on our moon have resulted from meteorite hits.
A comet is a small body of ice and dust that moves around the sun in an elongated orbit. As a comet approaches the sun, it heats up and leaves behind a stream of hot, glowing gases and dust particles. We see this as the ‘tail’ of the comet.
Comets take many years to complete an orbit around the sun. For example, Halley’s Comet takes 76 years to go around the sun. Some comets come from outside the solar system, and after going around the sun they go back, perhaps never to return again.