What is Quasars?


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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What is the Milky Way?


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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What are the shapes of galaxies?


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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What are Black Holes?



Black Holes



In space there are stars in which gravity is so strong that nothing can escape from it—not even light. We call these stars black holes. The gravity of black holes is so strong that it pulls in nearby stars, drawing them towards it.



Astronomers believe that a black hole forms when a massive star runs out of energy and is crushed by its own gravity. A star that runs out of energy collapses and then explodes. The exploding star throws off its outer layers, but the remaining core continues to collapse and becomes a black hole.



Because black holes are invisible, they are hard for scientists to find. However, most astronomers believe our galaxy contains millions of them. Astronomers have found strong evidence for many black holes in our galaxy and in nearby galaxies.                                                         





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What is Star Twins?


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.




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How many types of nebula are there?


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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How do Stars Explode?


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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How can you find the pictures of stars?


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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What are different shapes of stars in the sky?


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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