Using a Telescope
- Observe astronomical objects through a telescope.
- Discover the results of varying magnification, aperture,
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
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
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
Solar System Objects
- Observe the following (if available). Address the posed
questions and note any other interesting or puzzling
- The Moon. Note its phase, the presence of
earthshine, and/or color differences between the
maria and highlands. Do these areas have the same
number of craters? Count craters and carefully
sketch the terminator.
- Planet(s). Note their position in the sky
and relative to the Sun and/or Moon. Estimate its
phase and position in its orbit relative to the
Earth and Sun. Sketch the location of any moons,
dark features and/or rings. Does the planet
appear spherical? What colors do you see?
- Other. Specify and describe in detail.
Include a sketch.
Stars, Galaxies and Nebulae
- Observe the following types of objects. Again be
descriptive and include sketches.
- Double star. Note the name of the star(s)
and any contrasts in color or brightness. Is this
a true binary (i.e., are they gravitationally
bound)? Can you see both with the naked eye?
Compare the naked eye and telescopic color(s).
- Cluster. Specify if globular or open, or
observe both if possible. Do you see individual
stars or a hazy blob? Estimate how many stars are
in the cluster. Do you see stars obviously not
part of the group? How can you tell? Note any
color differences between stars and sketch the
cluster. Does it have a clear shape?
- Galaxy. Specify the galaxy name and type
(spiral, elliptical, irregular). Note its
color(s), shape, brightness, etc. If it is a
spiral, estimate its inclination. Does the
brightness peak sharply towards the nucleus? Is
it visible to the naked eye?
- Nebula. Specify the cloud by name. Sketch
it carefully noting the location of associated
stars, bright spots and colored areas.
- Using the CCD camera on the 16-inch telescope, image a
couple of interesting objects observed earlier. Note the
object, its location in the sky, the weather conditions,
exposure time and magnification. Be sure to get several
hardcopies of your images and turn in one for lab.
- How does the time-exposed image compare to the
image you saw through the telescope with your
eye? Note shapes, sizes, the number of objects,
- Do certain objects yield more information than
others when exposed?
- Was any information lost in the long exposure?