Astronomy 264
Build a Telescope
Summary
This lab teaches you the principles that allow a telescope to magnify the
images of distant objects, and how to build a refracting telescope similar
to what Galileo Galilei used in the 17th century.
Concepts
In this lab, we study how a refracting telescope
magnifies and focuses light. A refracting telescope uses
lenses to focus the light from a distant object. Each lens is a specially
designed piece of glass that brings the light to a
focus behind the lens:
The distance from the lens to this focus is the
focal length. The focal lengths of the lenses determine
the magnification of the telescope!
The objective lens is the lens closest
to the object that we are viewing. The eyepiece
is the lens closest to our eye. The
magnification is the ratio of the focal lengths of these
two lenses:
Fobjective / Feyepiece = Magnification
Magnification allows us to enlarge the images of planets and nebulae so
that we can see more details. However, magnification is not the
most important feature of a telescope! Many objects, such
as stars and galaxies, are so far away that no matter how much we can
magnify them, they won't be any more visible. In this case, it's
much more important to have a bright image than a magnified image. The
brightness of the image is determined by the size of the objective
lens: the bigger the objective lens, the brighter the image.
Last updated on January 27, 2000.
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