* Electromagnetic waves are the medium of light: Light itself is a form of electromagnetic radiation. Electromagnetic waves travel through space as oscillating electric and magnetic fields. These waves come in different forms, with visible light being just a small part of the electromagnetic spectrum.

* Light years measure distance: A light-year is the distance light travels in one year. It's a unit of distance used for measuring vast distances in space, especially between stars and galaxies.

* The connection: Because light travels at a constant speed (approximately 299,792,458 meters per second), we can use the distance light travels in a year (one light-year) as a way to understand the immense distances in space.

Here's an analogy:

Imagine you're driving a car at a constant speed of 60 miles per hour. You can use the distance you travel in one hour (60 miles) as a unit to measure longer distances.

* If you travel for 2 hours, you've traveled 120 miles (2 x 60 miles).

* If you travel for 10 hours, you've traveled 600 miles (10 x 60 miles).

Similarly, light travels at a constant speed, and we can use the distance it travels in one year (one light-year) to measure astronomical distances.

In summary: Electromagnetic waves are the form of energy that light is, and light years are a way to measure the incredibly vast distances in the universe based on the speed of light.