My Science School

Mercury, closest to the Sun

Mercury is the nearest planet to the sun. It is a bare rocky ball covered with craters, much like our moon. Also like our moon, Mercury has broad, flat plains and steep cliffs.

Mercury spins and has day and night, but it spins very slowly. One day on Mercury takes 59 Earth days.

Mercury is very hot during the long day. Temperatures there reach higher than 400 °C. At night, temperatures take a big dip, sometimes to as low as -170 °C!

Mercury has a bigger temperature change than any other planet. This is because it is closest to the sun, and because it has very long days.

Mercury is a small planet. It could fit inside Earth two and one-half times. There are hardly any gases surrounding Mercury, so it has very little atmosphere.

Mercury is much closer to the sun than Earth is. So if you were standing on Mercury, the sun would appear much bigger and brighter.

Of course, you could not stand on Mercury in the middle of the day or night because it is either too hot or too cold. But scientists have explored it with a spacecraft that had no people on board.

The U.S. Mariner 10 was the first spacecraft to reach Mercury. Mariner 10 was a space probe. A space probe is a machine that explores space and sends information and pictures back to Earth. Astronauts do not travel in space probes. Scientists on Earth use computers to control space probes. On March 29, 1974, Mariner 10 flew within 740 kilometres of Mercury. It swept past the planet again on Sept. 24, 1974, and on March 16, 1975. During these flights, the probe took photographs of parts of Mercury’s surface. The U.S. space probe Messenger was launched in 2004 and began orbiting Mercury in 2011. Messenger became the first space probe to orbit Mercury. Messenger began to map the planet’s surface and study its magnetic field.

The Solar System

Our solar system contains the sun and the many objects that travel around it. Some are planets much larger than Earth. Others are tiny meteors and bits of dust.

The Sun’s Family

There are nine planets in our solar system. Each of them moves around the sun in a certain path. This path is called an orbit.

The first two planets, Mercury and Venus, are very close to the sun. The others are much further away. Two planets are much smaller than Earth. One is about the same size. And four are much bigger.

Like Earth and the moon, the other planets in our solar system reflect the sun’s light. That’s why we can see some of them at night.

The sun’s family also includes objects called asteroids, comets, dwarf planets, and meteoroids. Asteroids are small masses of rock or metal. Most of them move around the sun between the orbits of Mars and Jupiter.

Comets are frozen balls of ice, gas, and dust that travel around the sun. Comets have long shining tails.

Dwarf planets are small, nearly planet-sized objects that travel around the sun. Many dwarf planets are in the Kuiper belt, a region of space just beyond Neptune.

Meteoroids are chunks of rock or metal that move through space. When a meteoroid enters Earth’s atmosphere from outer space and begins to burn, it becomes a bright streak called a shooting star, or meteor.

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Moons of other planets

Earth is not the only planet that has a moon. Other planets do, too!

Mars has two little moons that are just lumpy chunks of rock. The largest of these, Phobos, is only about 27 kilometres wide. Mars’s other moon, Deimos, is about 15 kilometres wide.

Just how big are Mars’s moons? On a map, find the Cape Cod Canal, which separates Cape Cod from the rest of Massachusetts, U.S.A. The canal is 27 kilometres long. So Mars’s larger moon, Phobos, is as wide as the canal is long! Deimos is a little more than half that size.

Jupiter has at least 63 moons. A few of the smallest moons are smaller than some of the mountains on Earth. But the biggest, Ganymede, is bigger than the planet Mercury.

Saturn has at least 62 moons. Like Jupiter’s moons, Saturn’s are very different in size. Some are smaller than 10 kilometres in width. Saturn’s biggest moon, Titan, is bigger than Earth’s moon. Titan is also bigger than Mercury.

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High Tide, Low Tide

The regular rise and fall of the ocean is called the tide. The tide is caused mostly by forces of gravity from the moon. These forces produce two high tides and two low tides each day.

High tide takes place on the part of Earth that is nearest to the moon. At the same time, high tide also takes place on the part of Earth furthest from the moon.

This seems strange, but there are several reasons for tides. An important one is the way the moon’s gravity pulls on Earth.

On the side of Earth closer to the moon, the moon’s pull is slightly stronger than it is in the centre of Earth. On the opposite side of Earth, the moon’s pull is slightly weaker. High tide happens where the moon’s pull is strongest and also where it is weakest.

As Earth turns, the water sinks back down. After about six hours, this part of the sea is all the way down to what is called low tide.

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Life on the moon would be dark, quiet, and uncomfortable. But living there would definitely improve your high jump!

Earth’s sky looks blue during the day because the air on Earth scatters blue light from the sun in all directions. But there is no air on the moon to scatter sunlight, so its sky is pitch-black. On Earth, air carries sound. On the moon, no sound can be heard.

During the day, the moon’s surface gets hotter than boiling water. During the night, the moon is colder than the coldest place on Earth.

We are held on the surface of Earth by the pull of Earth’s gravity. When we weigh ourselves, we are really measuring how hard the gravity is tugging on us.

The moon’s gravity is weaker than Earth’s gravity. On the moon, you would weigh one-sixth as much as you weigh on Earth. If you weigh 27 kilograms on Earth, you would weigh only 4.5 kilograms on the moon! You could also jump six times higher on the moon than you could on Earth. And you could lift very heavy objects that you couldn’t even budge at home on Earth.

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The surface of the moon is not the same all over. In some areas, it has broad, flat plains covered with powdery rock dust. In other areas, it has rugged mountains. It also has billions of round holes in the ground called craters.

Some of the craters are no bigger than a pencil point. Some are the size of a car tyre. And some are really enormous. The biggest crater on the moon is over 1,000 kilometres across.

What formed the moon’s craters and mountains? Chunks of rock called meteoroids move around the sun, just as Earth and the moon do. Sometimes these meteoroids crash into the moon. The moon and the meteoroids are moving so fast that the meteoroids make craters in the moon’s surface when they crash.

When meteoroids strike, they usually form walls of rock around the craters they make. Many of the moon’s mountains are really walls made by meteors.

Picture Credit : Google

An eclipse of the Moon

The night is clear, and a bright, full moon is shining. Slowly, a dark shadow begins to fall across the face of the moon. The shadow seems to move along until it completely covers the moon.

This event is called an eclipse of the moon, or a lunar eclipse. It takes place when Earth comes between the moon and the sun. The shadow creeping across the moon is the shadow of Earth!

What is Phases of the Moon? The moon seems to change from a thin crescent to a full circle. Each time the moon looks different, we say it is in a new phase. A phase is a change in the moon’s shape as it is seen from Earth.

1. In the moon’s first phase, it can’t be seen at all. That is because the moon is between Earth and the sun. The sun is shining on the side of the moon that faces the sun, but there is no sunlight on the side that faces us. So all we see is darkness.


2. After a day or two, the moon moves to one side of us. Then we can see a tiny bit of the side that is lit by the sun. We call this phase a crescent moon.


3. After about seven days, we can see half of the moon’s sunlit side. This phase is called a half moon.


4. After about two weeks, the moon is halfway around Earth from where it started. Now we can see the whole side of the moon that the sun is shining on. We call this phase a full moon. The moon keeps moving, and the part we can see gets smaller and smaller. Finally, the moon is between Earth and the sun again.

Picture Credit : Google

The moon is made of cold, hard rock. It is not a ball of hot, glowing gas like the sun. Yet, somehow, the moon shines.

But the moon doesn’t give off its own light. It reflects light from the sun. That means light from the sun bounces off the surface of the moon and some of that light reaches us on Earth.

The moon does not really reflect sunlight very well. Most of the rock on the moon is rough and dark grey, not smooth and shiny like a mirror. But the sun’s light is so bright that even the tiny bit that is reflected from the moon makes the moon appears to be glowing.

Earth shines, too! It reflects some of the sunlight that falls on it.

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Myths about the Moon

Imagine that you lived in the world more than 2,000 years ago. Every night the moon appeared, but you had no idea what it was or why it seemed to change shape. Would you make up a story to explain it? Many ancient people did. Some early people thought the moon was a powerful god or goddess. The ancient Romans called their moon goddesses Luna and Diana. Diana was also the goddess of the hunt. The crescent moon was her bow, and the moonbeams were her arrow.

Some ancient people had stories about the moon and the sun together. Some Native Americans believed that the moon and the sun were brother and sister gods.

Some sky gazers saw figures like a cat, a frog, or a rabbit in the moon’s markings. Others saw the face of a man. Legends of various lands told how the “man in the moon” had been put in prison for stealing or for breaking religious rules.

Was there once life on the moon? Some people believed there was. A Greek writer named Plutarch told of moon demons that lived in caves. A German astronomer in the 1800’s, F. P. Gruithuisen, told of seeing a city on the moon through a telescope.

Even today, some people use stories to explain why the moon seems to change shape.

The San people of southern Africa tell one story that explains why the moon seems to change its shape. This story says that each month the moon almost dies. But it is reborn just in time to start life all over again. When this happens, it is seen as a thin sliver. For 13 nights, it grows until it becomes a full moon. The San celebrate this with three nights of dancing.

Then the moon begins to die again. For the next 13 nights, the sun, which the San see as the great hunter, battles the moon. Slowly the great hunter slices at the moon, until there is no moon left. For a few days, the moon seems to be dead. But soon it is reborn, and it begins growing again.

Picture Credit : Google

The Moon

The moon is the brightest object in our night sky. On some nights, the moon looks like a huge shining circle of light. On other nights, it looks like a thin, silver fingernail. But the moon does not really change its size or shape. And it does not make its own light. The light we see comes from the sun and bounces off the moon.

The stars are trillions of kilometres away. The sun is millions of kilometres away. But the moon is only about 384,000 kilometres away. As Earth moves through space, the moon is always beside it. The moon moves around Earth.

The moon is smaller than most planets and stars. If Earth were the size of a basketball, the moon would be about the size of a tennis ball.

The moon is a ball of grey rock. Some of it is covered with dust. It has no air and no water. Most living things that we know of could not survive on the moon.

Long ago, many groups of people in different places worshipped the moon. The ancient Romans named the moon Luna. Our word lunar means “of the moon”.

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Too much sun can hurt us

The sun is important for all living things. But too much of it can be dangerous.

The sun sends out invisible rays of light called ultraviolet rays. These ultraviolet rays often tan the skin of people who sit in the sun. But if we stay in the sun too long without protecting our skin, these rays can burn our skin. They can even cause skin cancer.

How can you protect your skin from sun damage? First, when you are in the sun, remember to cover your skin as much as possible and wear sunscreen. This will help block the harmful rays.

Sometimes ultraviolet rays can hurt your eyes or make them puffy. You can help protect your eyes from the sun by wearing sunglasses. And never look straight at the sun. Do not even look at an area of the sky close to the sun! It will damage your eyes. Scientists study sunspots safely by using solar telescopes and other special equipment.

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The sun has Chickenpox!

Have you ever had chickenpox? If you have, you probably remember that parts of your body were covered with spots. Scientists who study the sun say that sometimes it looks as if the sun has chickenpox, too!

But the sun’s dark spots, called sunspots, are not caused by a virus the way chickenpox is. Sunspots are caused by giant storms on the sun’s surface. From Earth, these storms look like dark dots because they are much cooler than the rest of the sun’s blazing hot surface.

Most sunspots start off in pairs and drift apart. Because they are so far away from us, they look small. But just one of these spots is bigger than the whole Earth!

Sunspots do not occur all the time. Sometimes, the sun’s surface is covered with them. Years later, there may be very few. Scientists have learned that they run in cycles of about 11 years.

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Maui Tames the Sun

Long ago, when the planet Earth was young, the sun sailed across the sky very fast. No matter how early people got out of bed, they couldn’t get enough work done because the sun would disappear. One evening, Maui told his brothers that he could tame the sun.

Maui asked his brothers to make a rope out of coconut fibres. But the fibres would not hold the sun. Then he had his brothers make a rope out of vines. But the rope would not hold the sun. Finally, Maui’s mother cut her hair and wove it into a net. This time, when the sun zoomed along, the net of hair caught it. Maui told the sun he would let it go if it promised to slow down. The sun agreed, and that is why we have time to work, play, and rest during the day.

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Myths about the sun

Long ago, people in many cultures throughout the world worshipped the sun. No wonder! Like us, they could not live without it. They depended on it for light, warmth, and even food. The following tales are about the sun gods of some long-ago peoples.

Old Man Sun lived among the San, wanderers in Africa’s Kalahari Desert. Light shone from his armpits whenever he raised his arms. The San children lifted the old man while he slept and threw him into the sky, where his light could shine on everyone.

The sun god of the Zuni, a Native American people, sent his sons to Earth’s people, who lived underground. The sons led the people on a difficult journey to the surface of the planet Earth. When they arrived, even the light of the morning stars hurt their eyes. And when the sun first rose, they cried out in pain. But soon they could look around and see the many beautiful things in their new world.

How did ancient people explain the apparent motion of the sun across the sky? The Greeks thought the god Helios drove it every day in a chariot across the heavens. The Egyptians said the god Re brought light to the world by sailing the sun across the sky in his boat. Maoris of New Zealand believed one of their heroes had fought the sun and crippled it, so that it limped across the sky.

Some peoples believed that an eclipse was a sign that the sun god was angry with them. They believed that prayer and offerings would calm the sun god.

The ancient Chinese had a different belief. They thought a dragon was actually eating the sun during an eclipse. They made noises to scare off the dragon so that it would leave the sun alone.

A Japanese story says that the first eclipse happened when Amaterasu, the sun goddess, hid in a cave. The other gods began singing, dancing, and laughing just outside the cave. Curious about the uproar, Amaterasu peered out and was surprised to see her own reflection in a mirror that the gods had made. As she paused, one of the gods took her hand and pulled her outside. The eclipse was over.

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It is the middle of the day. The sun shines bright in the sky. Suddenly, the sky seems to be growing dark! The sun seems to be disappearing! Soon the sun is nearly as dark as night and there is only a pale, fuzzy ring around it! What has happened?

The moon, which moves around the planet Earth, has passed between Earth and the sun. The sun is much bigger than the moon, but it is so far away from us that the moon seems to cover it up. When the moon is between the sun and Earth, the moon throws a shadow on Earth. The part of Earth covered by the shadow gets dark. This is a total eclipse of the sun, or a total solar eclipse.

Sometimes during an eclipse the moon covers only part of the sun. This is called a partial eclipse.

The sun’s rays can hurt your eyes, so never look directly at the sun - even during an eclipse!

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