Download The Historical Evolution of the Telescope

The Historical Evolution of the Telescope
Diego Benavides 0241824
Abstract
The telescope is a fundamental tool in the successful study of the universe. Since its inception, it
has undergone many redesigns and improvements through engineering practices. This paper
discusses these evolutions while considering its origins and functions.
Introduction
The study of the universe is observational, and depends to a large degree on the quality of a
specific tool used for observation: the telescope. Without it, astronomy as a science could not
exist [1]. A telescope gathers and focuses radiation from the electromagnetic spectrum, allowing
a large amount of data to be compiled and analyzed from objects at large distances from the
point of observation [3]. The data received may span the entire range of the electromagnetic
spectrum, and thus is not limited to optical images, although such a reference is popular. Many
types of telescopes are often employed in formal astronomical studies [2].
Origins and Evolution
The term telescope itself comes from a combination of Greek words meaning “far-seeing”, and its
primary purpose facilitates just that. It is contended that the first of such optical devices crafted for
remote observation dates back more than three thousand years, desgined by the Assyrians. The
credit for the first formal invention of the optical telescope, however, is bestowed upon a Dutch
eyeglass maker in the 1600s, Hans Lippershey. Shortly thereafter, a telescope would be built by
a revolutionary of science and used for cosmological study. Galileo Galilei constructed what is
now referred to as a Galilean telescope. This telescope uses the property of light refraction to
collect light at a convex objective lens and focus it on a concave eye lens [3]. Such a design finds
use even outside of astronomy, in areas such as photography or ophthalmology [4].
Since the Galilean telescope, there have been various improvements in optical instruments, with
the creation and refinements of refracting telescopes, reflecting telescopes (Newtonian scopes)
and combinations of the two [2]. But it wasn’t until just after World War II that new types of
telescopes would give cosmologists a drastically different, yet scientifically relevant, look at the
universe. The radio telescope emerged in 1932, after Karl Jansky designed receivers with
directive aerials sensitive enough to monitor background noise levels. The evolution of radio
telescopes has allowed for finer detail resolution, assisted in part by utilizing an array of
telescopes [1].
Submitted in partial fulfillment of Engineering 4H03 (Professor A.A. Harms)
In June of 1962, an Aerobee rocket was sent to space containing a Geiger counter for detecting
new radiation sources. Following this event, a series of satellites were developed in order to
detect X-Rays, gamma rays, and UV radiation [1].
Other advances in telescope technologies include the
Hubble Space Telescope and multiple mirror
observatories. Launched in 1990, the Hubble Space
Telescope orbits at 600 kilometers above the Earth’s
surface and completes a full orbit in approximately 97
minutes. This telescope has allowed astronomers to
resolve images from over twelve billion light years away
[5]. Multiple mirror telescopes (MMT) are Earth oriented
telescopes using an array of identical mirrors to increase
their resolution while eliminating the cost associated in
construction. Research and development in MMTs have
allowed arrays to overcome the drawback of image
distortion due to atmospheric turbulence [6].
Theory and Function
Optical telescopes fall into three categories: reflecting, refracting and catadioptric. The latter uses
a combination of techniques employed by reflecting and refracting telescopes.
The refracting scope was the first telescope to be constructed, and operates by using lenses to
refract light. As light propagates from one medium to another, it undergoes an energy change
known as refraction. If the incident light is not orthogonal to the boundary of the new medium, the
light will shift direction. By employing a series of two lenses, a convex objective and concave eye,
light entering the objective may be narrowly focused to a point adequate for observation [1]. This
is demonstrated in figure 2a.
Figure 2: Select optical telescopes
In 1670, Sir Isaac Newton successfully constructed a reflecting telescope in an attempt to solve
the chromatic aberration associated with the refracting scope. The reflecting telescope uses a
combination of flat and curved mirrors to focus light. This is demonstrated in figure 2b. The focal
length is set by selecting a distance from the mirror to the focal plane during construction of the
device [7]. Unlike the refracting telescope, there is no glass required in the manufacture of a
reflecting scope, and thus imposes no limitations as to the size of the scope that can be
constructed. Another reflecting scope, the Cassegrain (figure 2c), uses a parabolic primary mirror
and hyperboidal secondary mirror. The purpose of this design is to reduce the diffraction effects
due to support issues associated with the Newtonian design [3].
X-ray telescopes operate using charge-coupled device (CCD) detectors, microcalirometers or
transition edge sensors. Using a CCD, an image is obtained over an exposure time by allowing
single photons to charge individual CCD pixels. X-ray photons are capable of producing very
large charges in a CCD sensor. Microcalorimters, however, are only capable of detecting photons
one at a time. Despite this limitation, the lack of x-ray photons directed towards earth allows
microcalorimeters to be suitable for astronomical observation. Transition edge sensors are
essentially improved microcalorimeters where super cooled metals are kept near transition
temperatures. An x-ray photon will cause a transition and allow the instrument to record the
corresponding energy level of the incident x-ray [1].
Gamma ray telescopes are typically application or mission specific. As an example, NASA’s
Compton Gamma Ray Observatory, a space telescope, contains no less than four instruments for
the detection of gamma rays: a burst and transient source, an oriented scintillation spectrometer,
an imaging Compton telescope, and an energetic gamma ray telescope [5].
Ultraviolet telescopes are considered to be a subset of optical astronomy, however require much
greater optics, resolution and instrument tuning to detect [1].
Summary
The understanding and formal study of the universe has been long facilitated and perhaps made
entirely possible due to the creation of a single device. During this time the telescope has
undergone a series of changes and improvements, which may be shown in the form of a
heterogeneous progression as follows:
 refracting   reflecting   radio 



 telescope   telescope   telescope 
 lens   
 x  ray   space   gamma  ray 



  UV telescope 
 telescope   telescope   telescope 
Although not completely linear, this progression demonstrates the continual feedback that each
previous scope design had on the next. Additionally, it is worth noting that many of these scopes
are used in a complementary fashion by astronomers and cosmologists when studying the
universe. To conclude, the following table summarizes some of the differences between select
telescope types.
Table 1: Sample Telescope Comparison
Telescope Type
How it Works
Refracting telescope
Reflecting telescope
Space telescope
Multi-Mirror Telescope
Light refraction
through lenses
Reflection and
concentration of
light using
mirrors
Various scope
technologies in
one package.
Identical array
of telescopes,
allowing images
to be focused in
a central
location.
Benefits
 Low maintenance
 Inexpensive to
produce
 Thickness and
internal
imperfections not as
important
 Mirror can be
supported uniformly
 No limits in reflector
size
 Free from stray light
 Avoids atmospheric
turbulence
 Reduced size in
construction
 Reduced
construction time
 Reduced cost
Disadvantages
 Requires cool down time
to prevent lens distortion
 Chromatic aberration in
bright images
 Glass requirements in
size, weight and cost
introduce limits on size
 Maintenance required on
mirror surfaces
 Requires cool down time
to prevent mirror
distortion
 Suffers from coma
 Distortion of field of view
 Extremely expensive
 Susceptible to
temperature distortions
 Drive motors required to
move the array are
costly
References
[1] Blackwell, Basil & New Scientist (1984). Observing the Universe. Oxford: Basil Blackwell Ltd.
[2] Binney, James & Merrifield, Michael (1998). Galactic Astronomy. New Jersey: Princeton
University Press
[3] Telescope. (n.d.). Wikipedia. Retrieved October 23, 2006, from
http://en.wikipedia.org/wiki/Telescope
[4] Cheng, Desmond & Woo, George C. (2000). Technical Note: The calibration of a 2.5x
Galilean focusable telescope as an optometer for refraction. Ophthalmic and Physiological
Optics 20-4, 342-347
[5] NASA (2006) Retrieved October 25, 2006, from http://www.nasa.gov/
[6] Lloyd-Hart, Michael (2003). Taking the Twinkle out of Starlight. IEEE Spectrum 40-12, 22-29
[7] Astronomy Magazine. (2006) Retrieved October 25, 2006, from http://www.astronomy.com