WHAT TYPE OF MEASURING
UNIT WOULD WE NEED FOR
DISTANCES ACROSS SPACE?
LIGHT YEAR
How far is far?
How fast is fast?
What Is It?
A light year is the
DISTANCE that light
will travel, through a
vacuum, in 1 year.
Calculate Seconds
⬜
How many seconds are in a
year?
60 s
60 min
24 hr
365.25 days
1 min
1 hr
1 day
1 yr
⬜
31,557,600 s/yr
Why “ly”?
Light years are used to
measure the vast
distances in space.
⬜ In the universe, the
kilometer measure is too
small to use.
⬜
What is the fastest
speed we know?
The Speed of Light
Speed of Light
⬜
c = 299,792,458 meters
per second
or 186,000 miles per
second
Speed of Light
⬜ To get an idea of how fast
this is. . . light can travel
about seven times around
Earth in one second!
Other Values
⬜
⬜
One light year is approximately
5.880 trillion miles. Or 9 trillion
km.
The symbol for light year is “ly”.
History Seen
⬜
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.
⬜
⬜
An Example
It takes 8 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.
Example: Sirius
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 8 years ago. The
light left the star 8 years ago.
⬜