Download 8.8D Light Years

8.8D Light Years
Earth and Space
Light Years
Lexile 960L
1
A beam of sunlight streams through
your bedroom window, disturbing
the darkness. You blink the
brightness out of your sleepy eyes. It
is hard to imagine, but the beam of
light has traveled for over eight
minutes to reach your room.
Although this seems like a long time
for light to travel to reach us, it is
incredibly fast. The sunlight had to
cross the vast distance between Earth
and the Sun, a total of 149 million
kilometers. It moves through space
at 300,000 kilometers per second.
This is faster than any known object in the universe can travel. The speed at
which light moves is called the speed of light. The distance light can travel in
a year is called a light year. Even though a light year may remind you of a
unit of time, remember that it is actually measuring huge distances between
objects in space. Light years also help astronomers study the early universe.
2
Astronomers use light years as a way of measuring distances that are too
vast to use standard units such as miles or kilometers. The Sun, the closest
star to Earth, is 149 million kilometers away. Scientists could also say that the
Sun is eight light minutes away, since its light takes eight minutes to reach
Earth. If something were to suddenly happen to the Sun, we would not
know about it for eight minutes because that is how long it would take to
reach Earth. The next closest star to Earth, Proxima Centauri, is 4.2 light years
away. This means that it takes this star’s light over four years to reach Earth.
As astronomers observe Proxima Centauri, they are seeing how it appeared
4.2 years ago.
1 8.8D Light Years
Earth and Space
3
4
Light years also help scientists observe conditions at an earlier point in the
universe. As you gaze up into the night sky, the twinkling little lights that
you see may not even be present anymore. If a star is three million light
years away, then its light has traveled for three million years to reach your
eyes. If the star exploded into a red giant one million years ago, we would
not know it. The explosion would not be observed on Earth for another
two million years! What we see now is how that star appeared three
million years ago. Studying the stars is like peering back through time.
When scientists use powerful telescopes, like the Hubble Space Telescope,
they can see as far away as the farthest galaxies. These galaxies are over
13 billion light years away. In a sense, astronomers are looking back into
the beginning of the universe.
Light years are an important unit of distance for astronomers or other
scientists, who study the objects in the sky. Light years make enormous
distances easily manageable. They also provide a window into the past for
many objects in the universe.
2 8.8D Light Years
Earth and Space
1
2
3
What is a light year?
A
A unit of measure that shows
how much light is in one year
B
The distance that light can
travel in one year
C
The amount of time it takes for
light to reach Earth
D
The distance that a star travels
in one year
How do scientists use light years?
A
B
4
To report distances between
objects in spaces and study the
early universe
To measure how fast an object is
traveling and determine the
origins of the universe
C
To measure the amount of light
that a star produces and
determine how hot it is burning
D
To determine the age of an
object in space and study how it
was formed
3 Why is staring at a star that is three
million light years away like seeing
back into time?
A
Ancient astronomers looked at
the stars, too.
B
The star’s distance is far away
from Earth.
C
The age of the star is older than
Earth.
D
The star’s light has been
traveling for three million years
and the light shows how the
star looked three million years
ago.
Why is it possible for a star that is no
longer in space to still appear to
shine?
A
A new star took its place
B
Stars never burn out
C
It is a reflection from the other
stars in space
D
The light may have been
traveling for a very long time
and by the time the light
reaches Earth, the star is no
longer there
8.8D Light Years
Earth and Space
5
The sun is _____ light minutes from
earth.
A
two
B
eight
C
thirty-two
D
one
4