Download Star Light, Star Bright

Star Light, Star Bright...
By Laura G. Smith
Name: ____________________________________ Date: _______________________ Period:_________
How many stars can you see on a clear night? About 5,000 stars are visible from Earth
without the use of a telescope, but you can only see a fraction of them from any particular
viewing point at any particular time. With the help of a powerful telescope, it's possible to see
more than 3 billion of the hundreds of billions of stars in our Milky Way Galaxy.
1
Stars are huge masses of hot, glowing gases, made up of about 75% hydrogen, 22% helium,
and traces of oxygen, neon, carbon, nitrogen, and other elements. Hydrogen provides the fuel
for stars to release heat, light, and other forms of energy through a process called nuclear
fusion. When the center of a star reaches a temperature of 2,000,000 degrees Fahrenheit,
hydrogen gas is changed to helium gas. The extra hydrogen that is not used during nuclear
fusion is instead changed into energy. This energy is transferred to the surface of the star and
then passed into space in the form of light, heat, and radio waves. This release of energy is what
causes stars to "shine."
2
The combination of elements and amounts of each one found in a star is described as its
chemical composition. As the chemical composition of a star changes over time, its appearance
is also altered. For example, a star that is in the late stages of its existence may have exhausted
its supply of hydrogen fuel, causing it to burn helium and heavier elements. This causes the star
to expand greatly, transforming it into what is called a red giant. As the red giant loses material
on its surface, gravity causes the star to begin to collapse. As the star's pressure and temperature
increase, the star may explode into a supernova (a star that suddenly becomes extremely
bright). The star may then eventually become a white dwarf, which is the last visible stage of a
star. If the star continues to cool down and contract, it may become a collapsed star called a
black hole.
3
Astronomers learn about a star's mass, temperature, size, and distance from the earth by
studying the energy it gives off. The brightness or magnitude of a star indicates how much
mass the star has. A star's color indicates the temperature of the star's surface. Stars have a
spectrum of colors ranging from blue to red, with the hottest stars giving off more blue than red
(reaching surface temperatures of up to 50,000 degrees Fahrenheit). Stars with lower surface
temperatures (about 5,000 degrees Fahrenheit) give off more red than blue.
4
Stars are divided by size into four main groups: Dwarfs, as you might guess, are the
smallest stars. Maanen's Star, the smallest dwarf, has a diameter of 5,200 miles (about 2800
miles less than the diameter of the earth.) The next-largest group of stars, simply named
Medium-Sized Stars, includes the sun. The diameters of these stars range from one-tenth of
that of the sun to about 10 times greater than that of the sun. Stars classified as Giants have
diameters ranging from 10 to 100 times as great as the sun's diameter. Supergiants, the largest
stars, earn their name because of huge diameters measuring up to a thousand times that of the
sun. If one of these stars were placed in the center of our solar system, it would easily cover
Earth, Mars, Jupiter, and Saturn.
5
Great distances separate stars from the earth and from each other. The sun, our nearest star,
(about 93 million miles from the earth) appears different from the stars visible in the night sky
because it is about 250,000 times closer to the earth than the next closest star. The earth's
second-closest star looks like a tiny pinpoint next to the sun.
6
Although stars appear to stay in the same place in the flat-looking patterns of the
constellations, they are actually moving at high speeds that can be measured over long periods
of time by small changes in the stars' positions. This movement of stars is known as proper
motion and is separate from the apparent motion of stars across the sky. That apparent motion
is caused by the earth's rotation.
7
Star Light, Star Bright...
1. Heat and light is released from the surface
of stars through a process called
A. Star shine
B. Chemical composition
C. Nuclear fusion
D. Heat transfer
3. Each star maintains the same chemical
composition as all the other stars.
A True
B. False
5. Stars that have a surface temperature of
50,000 degrees Fahrenheit are mostly
________ in color.
A. Red
B. Yellow
C. Blue
D. White
7. The movement of stars that is measured
over long periods of time is referred to as
Apparent motion
Proper motion
Stellar motion
Slow motion
2. A "red giant" is a star that
A. No longer reflects light
B. Is in its last visible stage as a star
C. Has exhausted its supply of hydrogen
fuel
D. Has suddenly become very bright
4. As a star's pressure and temperature
increase, it may explode into a
____________________ causing a sudden
burst of brightness.
A. Supernova
B. Superstar
C. Star burst
D. Yellow dwarf
6. Astronomers learn about a star's mass,
temperature, size, and distance from the
earth by studying the
Movement of the star
Age of the star
Energy the star emits
Star's relationship to the sun
8. Explain what causes stars to "shine."