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LIGHT YEAR
How do they measure that far?
Light Year – the distance that light travels in 1 year which is equal to 9.46 trillion kilometers (in a
vacuum)
The symbol for light year is “ly”.
So, if Jupiter is 620 million kilometers away from Earth can light get from here to Jupiter in less than a
year?
Yes it can
Monoceros Nebula is 1000 trillion kilometers from Earth. How many light years is this?
Approximately 106
Calculate Seconds
How many seconds are in a year?
31,557,600 s/yr
Speed of Light
c = 299,792,458 meters per second or 186,000 miles per second
What is the fastest speed we know?
The Speed of Light
Other Values
One light year is approximately 5.880 trillion miles (mi).
Light travels 9.46 trillion kilometers (km) a year.
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 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.
So how many light years away is Sirius?
8 ly
