Introduction to Telescopes: Night Labs

bresser telescope

Learning Goals:аThis lab will allow students to gain hands-on experience setting up a telescope for nighttime viewing. Students will study how telescope optics work, and will be introduced to the features present on more modern, high-end telescopes and how these aid in finding and viewing objects in the night sky.


Set up and properly align a telescope for nighttime viewing. Determine the magnification of a simple refracting telescope.

Resources: аWorksheet, Galileoscope, reflecting telescope, tripod, iPad, meter stick

Terminology: аfocal length,аright ascensiondeclination

Tutorials: none

Demos from UNL:аAtmospheric Effects, Frequency Allocation Chart, Galileoscope Instructions, telescopes


Refracting telescopes use lenses - doubly-curved pieces of glass or another transparent material - to focus light. This has the effect of brightening an image, magnifying it, and improving the available angular resoltuion. A single lens will produce a clear, in-focus image at a point that depends on its focal length, as shown by the equation below.


lens eqn

For nearby objects, the position of the focused image S2аchanges depending on the distance of the object. What happens when the object is very far away, essentially at infinity?

The magnification of the telescope is determined by both the focal length of the objective lens, fo, and the focal length of the eyepiece, fe.

а а а а а а а а а а а а а а а а а а а а а а а а а а а а а а а а а а а а а а а

а а

A problem encountered with refracting telescopes is that glass lenses bend light differently depending on frequency. This causes an effect called chromatic aberration, in which the colors in the image are distorted and out of focus. The effect can be corrected for by combining two lenses of slightly different refractive indices. One lens is converging, the other diverging. The dispersion in one lens is canceled out by the dispersion of the other, and light of different colors is combined properly at the focal plane.


ай 2017 University of Iowa