Instrumentation on Modern Telescopes
Modern Photography was not available to astronomers before the late 1800s. All images where simply sketches made by the astronomer viewing with their naked eye. But the mind has a way of altering the truth (as well made by the astronomer Percival Lowell who claimed to see artifacts on Mars from Advanced Civilizations!).
The advent of CCD Technology
IMAGING
SPECTROSCOPY or SPECTROPHOTOMETRY
Early Photography
Photographic plates were one of the earliest forms of photographic film, in which a light-sensitive
emulsion of silver salts was applied to a glass plate. This form of photographic emulsion largely
faded from the consumer market in the early years of the 20th century, as more convenient and less
fragile films were introduced. However, photographic plates were in wide use by the professional
astronomical community as late as the 1990s. Such plates respond to ~2% of light received.
CCDs (charge coupled devices) were invented at Bell Labs in the mid 1970's. Unlike photographic plates,
they detect 90% or more of the light that falls on them. CCDs work under the physical concept
which was first explained by Einstein, in 1905 (and for which he won the Nobel Prize), the
photoelectric effect. He explained the current flow of electrons which takes place
between two plates, when light is exposed to them. Today, CCDs make use of this current flow
to create charge in small wells (thousands of pixels across the surface) on crystal silicon surfaces.
The more light photons that hit the silicon, the more electrons accumulate. It is possible to
localize these potential wells in to very small areas, thereby generating an "image" of the
light strength as a function of position on the plate. Digital camera's widely available now
adays make use of this same technology.
This is nothing more than taking a picture. Many of the pictures you will see once we begin
studying the characteristics of our solar system will have been images taken with modern
CCD Camera's either from telescopes on the ground,
telescopes in orbit around the Earth,
telescopes on route or orbiting other planets, or even from the
surface of some planets.
For some of the all time best astronomy images available, see this website:
Astronomy Picture of the Day.
As early as Newton's time, people where already making spectra: rainbows with light.
Newton wrote all about it in his famous book, Opticks (1704), still available on
amazon.com! Modern astronomers use spectra to give them information about the
temperature, velocity, and chemical composition of astronomical objects. (see page 14)
Again CCD devices are used to detect the very weak light which is spread out via a
grating, prism or grism (combination grating and prism).
