Download How Big Is A Light Year?

Name: ______________________________________________________ Period: _______ Date: ____________
How Big Is A Light Year?
Directions: In the space below, calculate how large a light year is in miles. Use the speed of light provided by your teacher.
C (speed of light) =
1 light year =
Outside our solar system, stars are so far away that standard units of measurement like miles
and kilometers are awkward to measure these distances, therefore a unit known as the light
year is used. A light year is defined as the distance that light travels in one Earth year. Light
moves extremely fast, 300,000 km/s or 186,000 miles/second. In one second light can travel
around Earth almost four times.
Because light travels so very fast, everything appears to happen instantly in our everyday
experience. If we are watching the Philadelphia Eagles kick a field goal, we assume that the
ball was kicked right at the moment that we saw it. In actuality we must see the light that is
being reflected from the ball, and it does take time for the light to travel from the ball to our eyes. If the distance from the ball
to our eyes were 10 m, the light reflecting off the ball would take only 300 millionths (.000003) of a second to reach our eyes,
thus making it seem instantaneous.
Alpha Centauri, the nearest star to the Sun, is over 4 light years away, meaning the light we see from it took over four years to
travel to our eyes. It also means that what we see happening at that star is actually what happened four years ago, not what
is happening in the star’s present.
1) Light years are used to measure ____________________ rather than time.
2) Imagine that there is a planet with intelligent beings on it that's 20 light years away from Earth. These beings have an
extremely powerful telescope and can actually make out details of what is happening on Earth. If they aim their
telescope at the White House in Washington, DC, who would they find living there as the president and first lady?
3) If the red giant star, Betelgeuse, is 520 light years away, and it blew up in a supernova 150 years ago, what year would
it be when we actually see the explosion?
4) On another imaginary planet, someone is looking through a high powered telescope aimed at Earth, and is observing
the birth of America, as Thomas Jefferson pens the Declaration of Independence. How many light years away is the
planet from Earth? How many miles away is it?
____________________ light years;
_________________________________________ miles
5) Is a light year a useful unit when measuring distances within our solar system? Why or why not?
(HINT  Pluto is about 4 billion miles away from the Sun.)
Famous Astronomers
Directions: Match the famous astronomer to the quote that makes the most sense.
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Tycho
Galileo
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Kepler
Ptolemy
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Hubble
Copernicus
1) “I’ve finally worked out a mathematical explanation as to why
planets orbit the sun and moons orbit planets. It is gravity that
keeps an object in orbit!”
2) “The Earth is the center of the universe, and all of the planets and
stars orbit our planet. How do I know? Well, my theory predicts the
motion of the planets better than any other theory of my day.”
3) “Using large telescopes, I’ve discovered that all the other galaxies
out there are moving away from us; in other words, the universe is
expanding, as if it exploded in some sort of ‘Big Bang’! Gee, I sure
hope someone names a famous space telescope after me
someday!”
4) “I prefer the theory of the sun-centered universe over other
theories. This handy device called a telescope has helped me to
discover that the planets are not just dots of light, but physical
bodies like the Earth.”
5) “After several years of very precise observations, I conclude that
our universe is Earth-centered. Furthermore, the sun and the
moon revolve around the Earth, while the other planets revolve
around the sun.”
6) “For centuries people have been thinking that the Earth is at the
universe’s center, but I’m certain that it is, in fact, the sun at its
center. And, though it is not an accepted theory these days, I am
certain that the planets orbit the sun.”
7) “I do not agree with my mentor’s theory that the sun revolves
around the Earth. I have used his precise data to propose another
theory in which all of the planets revolve around the sun in
elliptical orbits.”
8) “As one of the most famous ancient Greek philosophers, I asked
questions about the universe and our place in it. Many people
consider me to be one of the first scientists ever.”
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Newton
Aristotle