Energy can take one of two forms: matter and light (called electromagnetic radiation). Light is energy that can travel through space. When you feel the warmth of the sun on your arm, that’s energy from the sun that traveled through space as infrared radiation (heat). When you see a tree or a bird, that’s light from the sun that traveled as visible light (red, orange… the whole rainbow) reflecting and bouncing off objects to get to your eye. Light can travel through objects sometimes… like the glass in a window.

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### 2 Responses to “Light is a Wave”

1. We talk about light years in the Astrophysics class, but here’s something you can try.

It’s totally understandable how it’s confusing, since the word “year” is contained in “light year” but is a measure of distance. Ask him to measure things he’s familiar with first – use a ruler to measure hands, feet, fingers, etc. Then ask him to measure larger things, like the driveway and give him a yardstick, showing him where the smaller increments (cm or inches) are on the yard or meter stick.

Now ask him how he’d measure from your town to the next – would he use a ruler with inches on it? Yardstick? Tape measure?

No – he’d want to try a bigger ruler, something with feet or yards on it. One measurement increment can be found on the other the larger you go.

Now try this if he’s ready… light travels at 186,000 miles per second. So how far does light travel in one second? (If that’s too big of a jump, back up and try it with car speeds while you’re driving – use kph or mph to talk about distance per unit time… our car is traveling 65 miles every hour, etc).

Go back to light – light travels 186,000 miles per second. How far does it go in one second? Two seconds? (2×186,000 miles) Ten seconds? (1,860,000 miles) 100 seconds? Etc…

How about a day? Week?

A year? Light travels 5,865,696,000,000 miles in one year. That DISTANCE is a light year. Instead of saying “5,865,696,000,000 miles” we say “one light year”. So if a star is one light year away, it’s really 5,865,696,000,000 miles away.

And last, give it time. Just because it doesn’t appear to make sense today doesn’t mean it won’t tomorrow. I know I have needed time to really understand things like this myself. 🙂

2. JP says:

I have an 11-yr-old Asperger’s son. I can’t get him to understand “light years.” No matter how my husband or I explain, he’s just not getting it. And he’s extremely intelligent. Help?