An astronomical telescope resolves distant sources that cannot be resolved with the unaided eye.
Like the microscope, the telescope does this by increasing the angular separation of the focused spots on the retina.
Unlike the microscope that resolves nearby point sources, the telescope resolves sources at infinity.
The initial screen shows two distant sources. Each emits parallel rays but the two sets of rays form a small angle between them.
Note that both sources are focused approximately on the same spot at the retina.
Click "Scope In" to place a telescope between the eye and the sources.
Drag the eyepiece until the resolved sources are focused on the retina.
In addition to resolving distant sources, an astronomical telescopes gathers all the light that crosses its objective.
Dim sources become brighter when seen through a telescope. The animation clearly shows how this happens.
Credits
Authored by Kevork Spartalian, University of Vermont, based on Davidson College physlets.