Transcript Light Year - Killeen ISD

Light years are units of time used to
measure the distance between objects in
the universe.
— Why is a light year a unit of distance
rather than time?
— Why do we need to use light years as a
way of measuring cosmic distances?
— What is the speed of light?
— How are light years used to measure
distances in the universe?
Why is a light year a unit
of distance rather than
time? It measures
the distance light travels in
a vacuum in one year - 9.5
trillion km or 5.880
trillion miles.
Why do we need to use light
years as a way of measuring
cosmic
distances? If we used
conventional measurements,
the numbers would be
huge and difficult to calculate.
What is the “speed of light”?
What is the “speed of light”?
The rate at which light travels
through
empty space - 299,792,458
meters/second or 186,000
miles/second.
How are light years used to
measure distances in the
universe? If
we know how fast light can travel
from a particular distance (the
Sun), we
can apply this to other objects in
our universe.
How far is far?
How fast is fast?
A light year is the
DISTANCE that light
will travel, through a
vacuum, in one year.

How many seconds are in a
year?
=

31,557,600 s in a yr
The Speed of Light
c
= 299,792,458 meters
per second
or
186,000 miles per second
 To get an idea of how
fast this is. . . light can
travel about seven times
around Earth in one
second!


One light year is approximately
5.880 trillion miles or 9.5 trillion
km.
The symbol for light year is “ly”.

Light years are used to
measure the vast distances
in space.
 In the universe, the
kilometer measure is too
small to use.

Every time you look at
objects in the night sky or
the Sun, the light from
that object is old. You are
looking at history.


It takes eight light minutes for
light leaving the Sun to reach
the Earth.
To put this in perspective, if you
could drive from the surface of
the Sun to the surface of the
Earth, it would take you 180
years driving nonstop at 60
mph.


Sirius, in the constellation Canis
Major, is the sky’s brightest star. It is
easy to find on winter and spring
evenings.
When you look at Sirius, you are
looking back in time to see how
Sirius looked eight years ago. The
light left the star eight years ago.
After your essay on Thursday
and in class on Friday, you will:
Develop a scale drawing that
represents the comparative distances in
light years between three objects in the
universe. Include a statement
discussing the advantages and
limitations of using a scale drawing to
represent large distances.