CSCOPE GRADE 8 UNIT 10

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 one year.

Calculate Seconds How many seconds are in

a year?

31,557,600 s/yr

60 s 60 min 24 hr 365.25 days

1 min 1 hr 1 day 1 yr ¿

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 9.5 trillion km.

The symbol for light year is “ly”.

Why “ly”? Light years are used to measure the vast distances in space.

In the universe, the kilometer measure is too small to use.

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 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.

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 eight years ago. The light left the star eight years ago.