How long would it take something to travel 1 light
year or 30 million light years?
A particle of light (called
a photon) would take exactly one year to travel a light year. This is
the definition of a light year. Thus, in order to calculate the
distance traveled by light in one year, we must first know how fast
light travels. It travels approximately 300,000 kilometers per second.
Then we must know how many seconds are in a year - approximately
32,000,000 in one year. So, multiply 300,000 kilometers per second by
32,000,000 seconds, which gives you about 9000 billion kilometers.
It is easier for astronomers to measure distances in light years,
because the Universe is so huge!