Light Years Notes

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/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.