ORION: Constellations

In ancient times when people looked up at the starry night sky, they thought they saw shapes in groups of stars. We call these shapes constellations. The ancient Sumerians, Babylonians, Egyptians, Greeks, and Chinese named constellations of stars after heroes and beasts from stories and after everyday objects.

You probably know some constellations. The Big Dipper looks like a giant pot with a long handle. The constellation Orion is named after a hunter in Greek mythology. You can see his belt, marked by three bright stars, and his sword, which hangs from his belt.

The stars that form constellations are not really near each other. Some of the stars in a constellation are much farther from us than others. The stars just happen to form patterns as we view them from the Earth.

WHICH CONSTELLATION IS WHICH?

When you look up at the sky, you see shapes much like those which the ancient stargazers named after characters from magical tales. You can use a star chart, a map that shows where stars appear in the sky, to become familiar with the shapes and names of the constellations. As the night passes, these great shapes seem to move through the sky, just as the Sun appears to cross the sky during the day. But it’s actually Earth that’s moving, not the Sun and stars.

You can only see the brightest stars with the naked eye. Try looking at the sky through binoculars or a telescope. Thousands of fainter stars come into view. You can no longer see the shapes of constellations.

DO CONSTELLATIONS ALWAYS LOOK THE SAME?

Because Earth tilts as it circles the Sun, you see different constellations at different times of year. The Big Dipper, for example, is easiest to find during summer. Orion is most visible during winter.

People in Australia and elsewhere in the Southern Hemisphere see completely different constellations than people in Canada or the United States. One of the most famous southern constellations is Crux, the Southern Cross.

The shapes of constellations slowly change over very long periods of time. The familiar forms will look quite different many thousands of years from now.

HOW DO ASTRONOMERS USE CONSTELLATIONS?

Astronomers divide the sky into 88 constellations. Even though the constellations do not represent real groupings of stars, astronomers still find them useful for naming stars and mapping the sky.

Astronomers use letters of the Greek alphabet to name stars. They also use a form of the name of the constellation the star is in. The brightest star in a constellation has alpha in its name, because alpha is the first letter of the Greek alphabet. For example, the brightest star in the constellation Perseus is called Alpha Persei. And the second brightest is Beta Persei. (Beta is the second letter in the Greek alphabet.) The star closest to the Sun is Alpha Centauri, the brightest star in the southern constellation of Centaurus.

Some objects that are not stars are also named after the constellations in which they appear. Such objects include the Andromeda galaxy and the Orion nebula. At certain times of the year, the Earth passes through showers of meteors (shooting stars). Even these meteor showers, such as the Perseids and Geminids, are named after the constellations from which they seem to fall.

WHAT ARE THE CONSTELLATIONS OF THE ZODIAC?

The ancient Babylonians noticed that the Sun’s position in the sky changes through the year. They divided the stars along the Sun’s path into 12 constellations. We call these 12 the constellations of the zodiac. They consist of Aries, the Ram; Taurus, the Bull; Gemini, the Twins; Cancer, the Crab; Leo, the Lion; Virgo, the Virgin; Libra, the Balance; Scorpio, the Scorpion; Sagittarius, the Archer; Capricorn, the Goat; Aquarius, the Water Bearer; and Pisces, the Fishes.

Black Holes

Black holes are some of the strangest things in space. A black hole sucks in anything that gets near it. Nothing can escape from a black hole—not even light.

BLACK HOLES ARE STRONG

Nothing escapes from a black hole because its gravity is so strong. Gravity is a force that pulls one thing to another. Gravity is the force that holds you down on Earth. When you jump up, Earth’s gravity pulls you right back down. Earth’s gravity also makes the Moon orbit (go around) Earth.

The more matter (stuff) that is packed in a star, planet, moon, or other object, the stronger is its gravity. Gravity makes an object with more matter pull an object with less matter toward it. The Sun has a lot more matter than Earth. The Sun’s gravity pulls on Earth. It makes Earth orbit the Sun.

Matter is packed very tightly in some things and loosely in others. The matter that makes up an iron ball is packed much tighter than the matter that makes up a bag of feathers. A scientist would say that an iron ball is much denser than a bag of feathers.

A black hole is denser than anything you could imagine. A black hole could have a million times more stuff than our Sun. All of this stuff would be packed into an area smaller than a city. The force of gravity from so much stuff packed into such a small area is awesome.

WHERE DO BLACK HOLES COME FROM?

Astronomers and physicists think black holes come from dying stars. A dying star burns out and stops shining. All the stuff that makes up the star starts falling in on itself. The star gets denser and denser. If the star is big enough and has enough matter, it could get dense enough to become a black hole.

STUDYING BLACK HOLES

No one has really seen a black hole. You cannot see black holes because they do not give off any kind of light. Physicists used math to predict that black holes exist.

Astronomers look for signs of black holes. Astronomers study powerful rays coming from stars in deep space. The stars seem to be orbiting black holes. Astronomers think that black holes are sucking gas from the stars, and this makes the stars give off X rays.

Galaxies are enormous groups of stars. Astronomers think that most galaxies have huge black holes at their centers. The Hubble Space Telescope took pictures of a disk of hot gases at the center of our own Milky Way Galaxy. Astronomers think this disk is going around an enormous black hole right in the center of our galaxy.

Milky Way

When you look up at the sky on a clear night, you see thousands of tiny points of light. A couple of the brightest points might be planets in the solar system. The rest are all stars. If you look closely, you might see a thick glowing band of faint white light crossing the sky. To see it, you’ll need to be somewhere without many streetlights. Ancient Greeks named this band of light the Milky Way.

The Sun is a star. It’s a lot closer to Earth than any other star, so it appears a lot brighter. The white glow of the Milky Way is made by billions of stars so far away that our eyes can’t see them as individual points of light.

WHAT IS THE MILKY WAY?

The Milky Way is a huge group of stars called a galaxy. There are billions of stars in the Milky Way. The Sun and all nearby stars are part of the Milky Way Galaxy. There are also huge clouds of gas and dust in between the stars. New stars form in the clouds of gas and dust.

The Milky Way Galaxy is shaped like a thick disk turning in outer space. There is a big bulge at the center of the disk. Curved arms spiral into the central bulge. The whole thing looks like an enormous whirlpool or pinwheel. Our Sun and solar system are in one of the whirlpool’s arms out toward the edge of the disk. That’s why the Milky Way looks like a band of light in the night sky. We’re looking at the edge of the disk instead of the round face.

The Milky Way turns slowly. Everything in the Milky Way orbits (circles) the center of the galaxy. It takes about 250 million years for our solar system to go once around the center of the Milky Way.

Astronomers think there might be an enormous black hole at the center of the Milky Way. A black hole sucks in everything around it. A black hole is invisible. Not even light can escape from a black hole.

The Milky Way is not the only galaxy in the universe. With powerful telescopes, we can see billions of other galaxies. Many of them are shaped like our own Milky Way, but some look like giant balls or strands of trailing stars.

HOW BIG IS THE MILKY WAY?

The Milky Way is huge. The entire Milky Way is about 100,000 light-years across. Astronomers measure great distances in light-years. One light-year is how far light travels in one year. Light travels extremely fast. A flash of light goes almost 6 trillion miles (10 trillion kilometers) in one year. That’s a 6 with twelve zeroes after it: 6,000,000,000,000! Even at that blazing speed, it would take a flash of light 100,000 years to cross the Milky Way.

The bulge at the center of the Milky Way is about 10,000 light-years thick. Our solar system is about 25,000 light-years from the center of the galaxy.

Spiral Galaxy

The Milky Way is a spiral galaxy. Spiral galaxies look like giant whirlpools or pinwheels. They have long arms made of gas-and-dust clouds and stars. The arms spiral, or circle around, the nucleus (center).

GMOS-S Commissioning Team, Gemini Observatory/Public Domain

Milky Way Galaxy

Our solar system, which includes the Sun, Earth, and other planets, is just a tiny part of the Milky Way Galaxy. The Milky Way contains billions of stars!

Morton-Milon/Science Source/Photo Researchers, Inc.

Galaxies

You look at a map to find out where you are. A map can tell you what city you are in and what street you are on. But do you know where you are in the universe? For hundreds of years, astronomers—scientists who study things in space—have been trying to figure out where our solar system is in the universe. They have learned that our Sun is part of a huge group of stars called a galaxy. Our galaxy is called the Milky Way. The Milky Way is just one of billions of galaxies.

WHAT ARE GALAXIES MADE OF?

A galaxy is made up of millions or billions of stars. Big clouds of gas and dust swirl in space between the stars.

Astronomers believe that most galaxies have an enormous black hole in their centers. A black hole is an object with lots of matter packed into it. A black hole has a powerful pull of gravity. Gravity is the force that holds you to the ground and pulls a ball back down after you throw it up in the air. The gravity of a black hole is so strong that it sucks in and crushes anything that comes near. Not even light can escape from a black hole.

WHAT DO GALAXIES LOOK LIKE?

Galaxies come in different shapes. Some galaxies look like giant whirlpools or pinwheels. They have long arms made of gas and dust clouds and stars. These are called spiral galaxies because the arms spiral into the center. The Milky Way is a spiral galaxy.

The stars and clouds of gas and dust in a spiral galaxy move slowly in a circle. They orbit, or go around, the center of the galaxy. New stars form in the clouds of a spiral galaxy.

Some galaxies are oval or round in shape. These are called elliptical galaxies. Elliptical galaxies tend to have older stars. Few new stars form in elliptical galaxies.

Some galaxies do not have any particular shape. These are called irregular galaxies.

When galaxies come close to each other, their shapes can change. Sometimes galaxies collide with one another. Irregular galaxies may be galaxies whose original shapes were distorted by collisions.

HOW DO WE LEARN ABOUT GALAXIES?

Galaxies give off different kinds of light. Astronomers study the light to learn about the galaxies.

Galaxies give off rays of light our eyes can see. They also give off radio waves. Galaxies give off heat, or infrared rays, too. They also give off X rays and gamma rays. Even though our eyes can’t see them, radio waves, infrared rays, X rays, and gamma rays are all types of light. Astronomers have instruments that can detect each of these types. The different types of light provide clues about what galaxies are made of and how they form.

Astronomers figure out how far away a galaxy is by studying the light that comes from it. They have found galaxies that are very far out in the universe. The Hubble Space Telescope took pictures of galaxies that are 13 billion light-years away from Earth. A light-year is how far light travels in one year. Light travels fast—about 6 trillion miles (about 10 trillion kilometers) a year. Six trillion is a 6 with twelve zeroes after it: 6,000,000,000,000! These most distant galaxies are so far away that it took their light 13 billion years to reach Earth.

Astronomers looking through powerful telescopes have also found that galaxies clump together. They form big groups called clusters. The clusters also tend to be clumped. They form even bigger groups called superclusters. Our Milky Way is part of a cluster of about 30 galaxies called the Local Group. The Local Group is part of a supercluster called the Local Supercluster. Long strands of superclusters wind through the universe. These strands look something like a jumbled spiderweb, with galaxies strung along the threads and vast voids of empty space between the threads.

Galaxy M100

The Hubble Space Telescope captured this image of galaxy M100. It has a spiral shape like our own Milky Way Galaxy.

NASA/Liaison Agency

Milky Way Galaxy

Our solar system, which includes the Sun, Earth, and other planets, is just a tiny part of the Milky Way Galaxy. The Milky Way contains about 400 billion stars!

Morton-Milon/Science Source/Photo Researchers, Inc.

Distant Galaxies

There are billions of galaxies in the universe. Each one is made up of millions or billions of stars. A few of these galaxies appear in this photo.

UPI/NASA/REUTERS

Andromeda Galaxy

The Andromeda Galaxy, a spiral galaxy similar to our own Milky Way Galaxy, is the farthest object from Earth that you can see without a telescope.

Robert Gendler/NASA

Galaxies M86 and M84

Galaxies M86, center, and M84, right, are elliptical galaxies. Such galaxies are round in shape and are usually made up of older stars.

Royal Observatory, Edinburgh/AATB/Science Source/Photo Researchers, Inc.

Hoag’s Object

A ring of young blue stars surrounds a nucleus of older yellow stars in the galaxy known as Hoag’s Object.

STSCI/AURA/NASA

Hubble Space Telescope

Many galaxies have been discovered and photographed by the Hubble Space Telescope. Because the telescope orbits Earth, it can see far into the universe without any interference from Earth’s atmosphere.

NASA

ORION

Ini Aku

Saturday, March 5, 2011

Constellations

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