Stars, Constellations, Galaxies,
and Nebulae Facts

What do you know about stars?

What is it that shines and twinkles in the night sky? Astronomers have stuudied stars for centuries but only recently have begun to understand them. Stars, constellations, galaxies and nebulae are all related as you will see. When you are ready, click back to return to the Student Center or click below to explore again.

Stars | Constellations | Galaxies | Nebulae | Terms

Stars

Hubble Telescope view of the exploding star Eta Carina The picture at left shows a Hubble Telescope view of an exploding star called Eta Carina. The gas and dust will eventually spread out to form a nebula (see Nebulae Section).

For most of recorded history the Earth was thought to be the center of the universe and never moved. The constellations were named and stories were told about them as they appeared through the seasons. Without a telescope or other aid the stars seem to be just points of light that move across the sky at night. Some wandered about which we now know are planets. Let's look at some facts about stars.

Stars can be packed so close as to be seen as Star Clouds, grouped like a ball as in Globular Clusters or rather loosely assembled in Open Clusters. Patterns are called Constellations and parts of these like the Big Dipper in Ursa Major are called Asterisms.

Stars come in different sizes. Supergiant stars range from 100 to 1000 times the diameter of the sun and giants range from 10 to 100 times the diameter of the sun. Dwarf stars can be 1000 times smaller than the sun. Click here to learn about our sun.

Stars vary in color based on their approximate surface temperature.

Color

Temperature

Example

Constellation

Blue-White

36,000° F and up

Rigel

Orion

White

20,000° F

Vega

Lyra

Yellow-white

11,000° F

Capella

Auriga

Orange

7,500° F

Arcturus

Bootes

Red

5,500° F

Antares

Scorpius

Globular Star Cluster in Hercules An example of a globular star cluster is at right in the constellation Hercules.

There are other types of stars, too. Double Stars are two stars that look like one to the naked eye but separate in a telescope view. They may not be orbiting each other as in a true Binary Star but appear to line up that way. In an Eclipsing Binary, stars orbit in such a way as to eclipse each other as seen from Earth. Variable Stars are stars that vary in brightness by various reasons. Novas and Supernovas are exploding stars that are blowing off their outer shells.

Two examples below show the Ring Nebula, a tube of gas and dust around a nova star and the Veil Nebula showing how the Ring might look after it expands and fades into the interstellar medium.


Ring Nebula	Veil Nebula

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Star information for elementary students.
Ask NASA about stars.
Ask a NASA astronomer.
Parts of a star.

New! Click here to find out about "The Professor's Telescope", a new book by Chris Moreau, one of our advisors. Take an adventure with Eric to Saturn!

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Constellations

The picture at left is the Scutum region seen in the summer sky. Click on the image to see at a larger size. The pinkish and brownish areas are the Milky Way, the edge of our galaxy. Scutum is a constellation. A constellation is a pattern of stars. When you look in the night sky you see really bright stars and some around them that are not as bright.

Many cultures told stories about hunters, warriors, queens and kings, birds, bears, horses, and other figures they saw in the sky. They used these myths to teach their history and how they saw their place in the universe. See below for more about sky folklore. Constellations are now used to designate an area in the celestial sphere. We use the Greek and Roman names but other civilizations used different names and myths.

The Big Dipper is an asterism that is part of Ursa Major, the Great Bear constellation and the large "w" is part of Cassiopeia. A planisphere will tell you when each constellation can be seen in each month. The reason we can't see some constellations all the time is that they are up in our sky during the day. As the Earth orbits the sun different constellations become visible.

Star maps or charts are used to find constellations, variable or double stars, nebulae and other objects. Click on the month below to see how the constellations appear to move throughout the year in the Northern Hemisphere. Just follow a constellation as it appears each month at about 9 PM. Note that all the stars appear to move around the last star in the Little Dipper, Ursa Minor. This is the North Star also called Polaris. Click here to see all the maps on one page.

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Constellations tour by the Hawaiian Astronomical Society
Stanford's Solar Folklore
Native American Folklore
Native American Folklore Stories
Mayan Folklore
Japanese Starlore

Galaxies

The picture at left shows the Andromeda Galaxy and two companion galaxies. It is over 2.4 million light-years away from us. Click on the image to see a larger size view.

A galaxy is like an island in space made up of gas, dust and millions of stars. Our own galaxy, the Milky Way, includes about a trillion (a thousand billion) stars in a disk shape. Recent research indicates that there may be millions of galaxies in our universe. Galaxies are classified using Edwin Hubble�s scheme describing spiral, barred spiral, elliptical, peculiar and irregular shapes.

Top view of a spiral galaxy The spiral galaxy seen at right is like our own galaxy. We are about two-thirds of the way out on one of the arms of our galaxy. We are in a group of galaxies called the Local Cluster.

A few years ago the Hubble Space Telescope took an image called the Hubble Deep Field. It was a spot of sky near the Big Dipper about the width of a dime 75 feet away. Scientists counted over 1500 galaxies! Take that number times the volume of space in every direction and you would calculate that there are millions of billions of galaxies with billions of stars in each galaxy.

Nebulae

The Great Orion Nebula in the sword of Orion is pictured at left. Stars are being formed in the cloud of gas and dust. Click on the image to see a larger version.

Gas, dust and debris from star explosions and around star forming regions are called nebulae. A nebula can reflect light (Reflection Nebulae) or absorb light (Dark or Absorption Nebulae) while Emission Nebulae emit light on their own. The remnants of a star explosion are called Planetary Nebulae because they looked like planets to early astronomers with small telescopes. Some are named because of their recognizable shapes like the Ring Nebula in the constellation Lyra.

The image at right is the Eagle Nebula in the constellation Aquila. You can see the darker clouds in the center look like a diving eagle. This emission nebula glows red because of hot hydrogen atoms.

Click on the image to see a larger view.

Terms

Here are some basic terms used for describing star patterns, galaxies and nebulae. Find more terms in the Glossary.

Asterism: A named group of stars that is part of a constellation, the Big Dipper is one.
Celestial Equator: The imaginary line around the sky directly above the Earth's equator.
Celestial Pole: Points above the Earth's north and south poles.
Celestial Sphere: An imaginary sphere surrounding the Earth where the sun, planets and stars are, a 3 dimensional map of the universe. Click here for more about the celestial sphere.
Constellation: A pattern of stars usually named after animals or people in stories. Now used to designate an area in the celestial sphere.
Ecliptic: The path the sun seems to follow in the sky.
Emission Nebula: A cloud of glowing gas.
Globular Star Cluster: A group of stars that look like a shape of a ball.
Light-year: The distance light travels in a year. About 10¹³ km or 6 trillion (thousand billion) miles.
Nebulae: A glowing clouds of gas or dust reflecting the light of nearby stars.
Open Star Cluster: A group of stars that look close together in the sky.
Orbit: The path an object takes as it moves around another object.
Planetary Nebula: An expanding ring of gas around a star.
Reflection Nebula: Dust and gas reflecting light from stars close by.
Rotation: An object spinning about its center.
Zenith: The point in the sky directly overhead.