### Light Year

A light year is a measure of distance. It is very far. Scientists use the light year to help understand the great distances in space. The nearest star to us is about 4.2 light years (or 40 trillion kilometers) away. If you could travel at the speed of light, it would take you 4.2 years to reach that star.

A light year is simply the distance light can travel in one year. Since light can travel 300,000 km (186,000 miles) in one second, can you imagine how far it can travel in one year?

To figure this out:

Multiply the speed of light (300,000 km/s) by 60. This is the distance light travels in one minute (18,000,000 km ).

Now multiply that by 60 again. This is the distance light travels in one hour (1,080,000,000 km).

Now multiply that by 24. This is the distance light travels in one day (25,920,000,000 km).

Finally multiply by 365. This is the distance light travels in one year (9,460,800,000,000 km). This is called a light year. That is nearly 10 trillion kilometers or about 6 trillion miles. That is about 1,600 times the distance from the sun to Pluto. Since Pluto is about an average of 5,916,000,000 km from the sun, it takes light from the sun about 5 and 1/2 hours to reach Pluto. It would take about a year for light to travel from the sun to Pluto 1,600 times.

Teachers: click here for a great web site with information on light year and many other concepts.

Source: The Cosmic Perspective