University of Michigan - Department of Astronomy


updated: 04/19/2000

Using a Telescope



Since Galileo first pointed his spyglass to the heavens, our eyes have been opened to a broader universe. The telescope, even when used with the eye alone, reveals to us stars and other objects too faint to see normally, and the disks of planets and galaxies too small to see normally. With CCDs or film, the telescope acts as a light bucket, collecting photons to uncover the faintest objects. In this lab you will use telescopes to observe various types of objects, and understand the wealth of information attainable with these instruments so vital to modern astronomy.

The basic telescope consists of a main lens or mirror, typically called the objective or primary, which defines the aperture, or diameter of the light collecting area. A second lens, the eyepiece is used to realign the light rays for viewing, resulting in a magnified image. The magnification is the ratio of the focal lengths of the primary and the eyepiece, where the focal length is the distance between the lens and the focal point, where incoming light is concentrated.

Magnification = fo/fe

Note that the image is inverted (appears backwards and upside-down when compared to the object). The figure above is for a refracting telescope, that is one with a lens as the primary. Reflecting telescopes use a mirror as the primary, but the function is the same.

For the following sections, use a separate worksheet to sketch and describe what you are viewing through the telescope. Always include the magnification and specify which telescope is being used. Pay close attention to colors, subtle details and number of objects visible. Notice any differences between the telescopic image and the object's appearance to the naked eye. Vary the magnification, and note the differences you see. For submission, translate your notes and sketches into coherent observations.


Solar System Objects

Stars, Galaxies and Nebulae

Time-Exposed Observations