Chapter 3
The Telescope
Abstract The telescope is the principal tool of the astronomer. Therefore, it is
important to understand the type of telescope, the process by which the telescope
is mounted, its limitations, and the accessories available to the astronomer. Furthermore, since on occasion, telescopes suffer from optical problems, we show how to
identify such problems and to resolve them if possible.
3.1 Telescopes
Before beginning this chapter, we need to issue you a small but necessary warning.
Under no circumstances should you look at the Sun with any optical instrument or
with the naked eye unless the observation is by projection or with a special solar
filter. If you use a filter, I strongly suggest that you put a camera on to check that the
filter is not damaged before you put your eye to it. You can easily replace a camera,
but replacing your eye is not so easy. To illustrate the damage, some years ago, the
author was using a solar telescope mounted on a much larger telescope. Of course, I
put the lens cap on the main telescope, as pointing it at the Sun without the lens cap
would destroy the very costly astronomical camera mounted on it. Unfortunately, I
forgot about the small 5 cm finder scope mounted next to (and hidden by) the solar
telescope. In the two seconds between pointing towards the Sun and realising that
the lens cap was off and replacing it, the steel crosshairs in the finder scope melted.
Fortunately, finder scopes are cheap, but it was a lesson learned. So take heed, and
always double check!
A telescope has two functions, to gather light and to bring that light to a focus.
These manipulations may be achieved in two ways; we can refract the light by means
of lenses or employ mirrors to reflect it. You will typically be using a derivative of a
reflecting telescope, although your finder telescope or guide telescope, if you have
one, will normally be a refracting telescope. Likewise, if you use a solar telescope,
it is likely to be a refracting telescope.
Independent of its type, the telescope will have a number of important optical
characteristics that you should be aware of:
© Springer Nature Switzerland AG 2020
M. Gallaway, An Introduction to Observational Astrophysics,
Undergraduate Lecture Notes in Physics,
https://doi.org/10.1007/978-3-030-43551-6_3
23
The Telescope
Abstract The telescope is the principal tool of the astronomer. Therefore, it is
important to understand the type of telescope, the process by which the telescope
is mounted, its limitations, and the accessories available to the astronomer. Furthermore, since on occasion, telescopes suffer from optical problems, we show how to
identify such problems and to resolve them if possible.
3.1 Telescopes
Before beginning this chapter, we need to issue you a small but necessary warning.
Under no circumstances should you look at the Sun with any optical instrument or
with the naked eye unless the observation is by projection or with a special solar
filter. If you use a filter, I strongly suggest that you put a camera on to check that the
filter is not damaged before you put your eye to it. You can easily replace a camera,
but replacing your eye is not so easy. To illustrate the damage, some years ago, the
author was using a solar telescope mounted on a much larger telescope. Of course, I
put the lens cap on the main telescope, as pointing it at the Sun without the lens cap
would destroy the very costly astronomical camera mounted on it. Unfortunately, I
forgot about the small 5 cm finder scope mounted next to (and hidden by) the solar
telescope. In the two seconds between pointing towards the Sun and realising that
the lens cap was off and replacing it, the steel crosshairs in the finder scope melted.
Fortunately, finder scopes are cheap, but it was a lesson learned. So take heed, and
always double check!
A telescope has two functions, to gather light and to bring that light to a focus.
These manipulations may be achieved in two ways; we can refract the light by means
of lenses or employ mirrors to reflect it. You will typically be using a derivative of a
reflecting telescope, although your finder telescope or guide telescope, if you have
one, will normally be a refracting telescope. Likewise, if you use a solar telescope,
it is likely to be a refracting telescope.
Independent of its type, the telescope will have a number of important optical
characteristics that you should be aware of:
© Springer Nature Switzerland AG 2020
M. Gallaway, An Introduction to Observational Astrophysics,
Undergraduate Lecture Notes in Physics,
https://doi.org/10.1007/978-3-030-43551-6_3
23