My Science School

Around the Sun

Many hundreds of years ago, most people thought the moon, sun, planets, and even the stars all revolved around Earth! But in the 1500’s, a Polish astronomer named Nicolaus Copernicus taught people that the sun was at the centre of the solar system. He said that all the planets, including Earth, moved around the sun.

Copernicus was right about that, but he was not quite right about the paths the planets took. Copernicus thought each planet moved in a circular orbit around the sun. Another astronomer, Johannes Kepler, discovered that the planets moved around the sun in ellipses, or ovals, not in circles.

Kepler said that a planet is closer to the sun at certain times. He discovered that the planets move faster when they are closer to the sun and slower when they are further away from it. He also learned that the planets closest to the sun move faster than the others.

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The first Telescopes

The first telescope was probably invented in 1608 by a Dutch maker of spectacles named Hans Lippershey. He made his telescope by putting two lenses with slightly different shapes at opposite ends of a tube. The following year, after hearing about Lippershey’s invention, an Italian scientist named Galileo made his own telescope.

Galileo was one of the first people to use the telescope to look at objects in the sky. He made many important discoveries, such as the craters on the moon and the spots on the sun.

Galileo discovered four of Jupiter’s moons and learned that they went around the planet. He was the first to notice that Venus had phases, very much like our moon. He also discovered that the Milky Way Galaxy consisted of many stars.

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Telescopes make distant objects look bigger. Two main types of telescopes are refracting telescopes and reflecting telescopes.

A refracting telescope gathers light from a distant object and focuses it through two lenses. It has one big lens in front and a smaller lens you look through. The lens at the front usually has a bulge on both sides. It is thick in the middle and thin around the edges. This lens collects the light from a distant planet or star and forms an image of it in the telescope tube. The other lens, called the eyepiece, is like a very powerful magnifying glass. It makes things look much bigger.

A reflecting telescope uses a large mirror to collect the light, instead of a lens. The mirror is at the bottom end of the tube. The light from a star goes straight down the tube and strikes the mirror. Then the light is reflected up the tube. A smaller mirror reflects the collected light. The light comes out through a hole in the side of the tube, where the eyepiece is.

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Light show in the Sky

People who live far enough north or far enough south often see a light show called an aurora on clear nights. Great sheets of colourful light seem to ripple in the sky like curtains swaying in a breeze.

This light show takes place in Earth’s atmosphere, but it is caused by the sun. The sun shoots particles of matter into space. Many of these particles come to Earth. Near Earth’s North and South poles are two points that act like giant magnets. These points are called the north and south magnetic poles. These two magnets attract the particles of energy from the sun. When these particles collide with other particles in Earth’s atmosphere, they glow. They fill the sky with shimmering light.

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Waves from Space

Right this minute, you are being hit by waves from outer space. These are radiation waves, and space is full of them.

Radiation is the giving off of a certain type of energy. This type of energy is given off by most things in space, including the sun and other stars, planets, and the huge clouds of gas and dust called nebulas.

All life on Earth depends on the radiation given off by the sun. The sun’s energy provides heat and light. The heat warms Earth. Its light provides food for plants, which in turn feed animals and people.

Radiation waves travel incredibly fast, almost as fast as light. When radiation strikes an object, it may give some or all of its energy to the object. When radiation waves hit you, you can’t feel them because they are made of such tiny bits of matter. Earth’s atmosphere shuts out some radiation. Scientists think there is also a kind of “wall” in our solar system that stops other radiation waves as well. This is a good thing, because too much radiation can make people sick.

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Quasars

Out in space there are extremely bright objects that we call quasars. Most quasars are about the size of the solar system. But they can be a trillion times brighter than the sun.

The word quasar is short for “quasi-stellar radio source”, which is an object that looks like a star but is not really a star.

In photos of space, quasars look like stars. But we can tell that they are giving off as much light and heat as 100,000 Milky Way galaxies!

Quasars are travelling away from us very fast. And they are very far away. They are so far from us, we do not see them as they are now. We see them as they were about 15 billion years ago. Astronomers study them to find out what the universe was like so long ago.

Where do quasars get all their energy? Many astronomers believe that quasars have massive black holes at their centers. Energy comes from matter swirling in towards the black hole.

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The Milky Way

The Milky Way is the name of the Spiral galaxy in which we live. It is made up of hundreds of billions of stars, including our sun.

The Milky Way looks like a gigantic cloud of stars, all very close together. But the distance between any two Milky Way stars varies.

Just as Earth moves around the sun, the sun and the other stars move around the centre of the galaxy. The galaxy is so big, and our sun is so far from its centre, that it takes the sun more than 250 million years to go all the way around.

Our Galaxy Neighbours

We live in the Milky Way Galaxy, but there are many other galaxies in the universe. Most of them are so far away that we can’t see them without a telescope. But there are three galaxies that we can see with just our eyes.

One of these is the Andromeda Galaxy. It is bigger than our own Milky Way Galaxy and contains more than 150 billion stars.

The other two galaxies we can see without a telescope are the Large and Small Magellanic Clouds. They can both be seen from the Southern Hemisphere.

The Magellanic Clouds, the Andromeda Galaxy, and our galaxy, along with others, form a group of about 30 galaxies called the Local Group. Beyond the Local Group lies a whole universe of galaxies!

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The shapes of Galaxies

A galaxy consists of stars, dust, and gas held together by gravity. Small galaxies have fewer than a billion stars. Astronomers have photographed millions of galaxies through telescopes. They believe there are about 100 billion galaxies in the universe. Each galaxy may hold billions of stars.

Galaxies come in many different shapes and sizes. However, there are four main shapes that we can recognize in the sky.

A spiral galaxy looks like a giant whirlpool of stars with a flattened ball in the middle. Out of this ball come two or more spiral-shaped arms of stars. Our galaxy, the Milky Way, is a spiral galaxy.

A barred spiral galaxy has a sausage shape in the middle. From the ends of the sausage come two spiral arms of stars.

Elliptical galaxies are curved. Some are almost round. Others look like flattened balls or footballs.

Irregular galaxies do not seem to have any special shape. Some look like messy spirals. The Magellanic Clouds, the closest galaxies to ours, are irregular galaxies.

Many galaxies are grouped together in space. Such groups are called clusters of galaxies. Some galaxies stand alone between the clusters.

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Star Twins

Many stars seem to come in pairs, like twins. Some stars even come in triplets or greater numbers.

These multiple stars were formed at the same time, but they are often very different.

Sometimes a giant orange star is twinned with a medium-sized blue star. Sometimes a yellow star, like our sun, is matched with a white dwarf star.

Twin stars affect each other. If one star is heavier than the other, the lighter one will orbit the heavier one. If they are about the same weight, they will orbit the same point in the sky.

Such twin stars are often so close together, and so far from Earth, that they look like a single, twinkling star. Only with special instruments and telescopes can we tell that there is more than one star.

Misty shapes in Space

In space, between the stars, there are big patches of gas or dust, or both. These are called nebulas or nebulae. Nebulas come from the Latin word for cloud.

There are four kinds of nebulas. One kind seems to glow because it reflects the light from nearby stars. This kind of nebula is made of gas and dust and is called a reflective nebula.

Other nebulas are collections of dust, gas, and special gases that give off their own light. They are called emissions nebulas.

Other nebulas are collections of cloudy dust and gas that often block the stars behind them or make these stars difficult to see. These are called dark nebulas.

Planetary nebulas have a flat, rounded surface like a planet. They are shells of gas that usually surround a star that has exploded.

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Exploding Stars

In the year 1054, a very bright star suddenly appeared in the sky. It was so bright that it could be seen in the daytime. Then it slowly began to fade away. After a time, it disappeared. What kind of star was this?

The disappearing star was a star that had exploded. Certain kinds of stars can explode. A small star called a white dwarf may suddenly flare up and become much brighter. Such a star is called a nova. After a time, the star’s brightness fades away.

When a very large star called a supergiant begins to die, it explodes, too. This explosion sends a gigantic cloud of glowing gas out into space. This kind of explosion is called a supernova.

A star that becomes a supernova may become a billion times brighter. The bright star seen in the sky in 1054 was a supernova.

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Finding Star Pictures

If you live in the Northern Hemisphere, you will be able to see the constellations, during most of the year. If you live in the Southern Hemisphere, you will be able to see the constellations, during most of the year. And if you live in the southern U.S.A., Hawaii, northern Australia, or somewhere else close to the equator, you will sometimes be able to see some of the constellations on both charts.

On the charts, stars in each constellation are joined with lines that show the constellation’s shape.

You will need a torch to see the chart, but be sure to cover the light with red cellophane. Otherwise, it will be hard to see the stars when you look up at the sky.

The constellations move into a different part of the sky each month. The names of the months are given around the outside of each chart. Hold the book so that the name of the present month is closest to your chest. The chart will then show where the constellations are when you look up at the sky.

On the charts, each constellation has a Latin name. Some of the names are based on what ancient people thought the constellations looked like. For example, in the Northern Hemisphere, there is a constellation called Draco, which means “dragon”. In the Southern Hemisphere, there is a constellation called Crux, which means “cross”. The charts also show a few of the brightest stars, such as Vega and Canopus.

If you live in or near a city, you may not be able to see all of the stars or constellations because of the city lights. But you will nearly always be able to see the brightest stars on cloudless nights.

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Star Pictures

If you look up at the sky at night, you might imagine pictures or shapes in the stars. Long ago, people used their imaginations to find star pictures, too. To some people, one group of stars looked like a hunter carrying a club and holding the pelt of an animal he had killed. Other star groups looked like a crab, a bull’s head, and even a dragon! People named star groups after the pictures they made.

Today, amateur astronomers still use these star pictures, called constellations, to find the stars they want to study.

Star Stories

In ancient times, when people found pictures in the stars, they made up stories to go along with the pictures. People of different cultures sometimes had different stories about the same group of stars. Here are just a few of those stories.

• Scorpio

The ancient Polynesians told a story of stars that were born in a canoe. Scorpio is the tail of the canoe. A story from Australia says Scorpio is a crocodile, an opossum, and a water bird.

• Cancer

Ancient Greeks tell a story that the goddess Hera was angry with Hercules, the son of the sky god, Zeus. While Hercules was fighting with a monster, she sent Cancer the crab to distract him. The crab was crushed by Hercules’s foot. Hera rewarded the crab by placing it among the stars.

• Gemini

Ancient Greeks said that twin brothers, Castor and Pollux, were the constellation Gemini. A story from northwest Siberia tells of two elks running away from two hunters. The twins of Gemini are the two elks.

The Indians of Mato Grosso, Brazil, told a different story. The sun gave three flutes to men and taught them to play tunes and dance. Gemini is one of the flutes.

• Cygnus

For thousands of years, many groups of people have seen this constellation as a bird. According to one story, the Greek god Zeus turned hiniself into a swan to become attractive to a woman. The Aleut people of Alaska tell about a man who set off to hunt seal in a kayak. The hunter dips his oar into the freezing water. Cygnus is the kayak, the oar, and the seal hunter.

• Orion, the Hunter

There are many stories about Orion, called the Giant by Arabs and the mummy of Osiris by ancient Egyptians. To ancient Greeks, Orion was a giant and great hunter turned into stars by the gods. Three bright stars in the constellation represent Orion’s belt, and five fainter stars below the belt are his sword.

An Australian story is about three fishermen who make up the constellation Orion. A story from central India tells of the Sing-Bonga. The Sing-Bonga went to the heavenly blacksmith. The blacksmith made an iron plough. The sword and belt of Orion are the plough. Auriga, a nearby constellation, is the blacksmith, the bellows, and the fire.

• Ursa Major, the Great Bear

The Micmac people of North America tell a story about a great bear that wakes from a long sleep in late spring. He is chased by seven birds. In summer, the birds chase the bear across the northern horizon. In autumn, one of the birds strikes the bear with an arrow. The bear falls on its back. Blood drips down to Earth and paints the leaves red. In winter, the bear’s spirit enters another bear. The next spring, that bear gets chased across the sky.

In the U.S.A. and Canada, the seven brightest stars of Ursa Major are called the Big Dipper. The Chinese believe that those seven stars form a bushel measure used to bring food to people during a famine. In India, the seven stars represent seven ancient sages, or wise people.

The Sia Indians of South America tell about a giant beetle who was given a sack of stars to carry from the underworld to the world above. The beetle was told not to open the sack, but he did. All the stars scattered across the sky. A few stars were left in the sack and these were used to make patterns in the sky. We call these patterns Ursa Major, Pleiades, and Orion’s Belt.

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