Here's why:

* Refraction: The bending of light as it passes from one medium (like air) to another (like glass) with a different density. This bending is due to the change in the speed of light as it travels through the different media.

* Refracting telescopes: These telescopes use lenses made of glass to bend and focus incoming light. The lenses are shaped to direct the light rays to a focal point, creating an image.

So, when light passes through the glass lenses of a telescope, it's refracted, and this refraction is the key principle that allows the telescope to gather and focus light to create magnified images of distant objects.