Perhaps one of the most well known is the Hubble Space Telescope which has brought us many stunning images of space such as this one of the Monkey Nebula
But why are there so many different types of telescope and why are so many of them located in deserts or at the top of mountains or even in space?
It all comes down to the fact that most light is in fact invisible to our eyes - the light that we see with our eyes is only a small proportion of all light.
The whole spectrum of light, visible and invisible is called the electro-magnetic (EM) spectrum. Astronomical objects emit light at many different wavelengths on this spectrum – the light of the stars that we can see with the naked eye is only a small part of the story they have to tell us.
So telescopes have been developed to observe all types of light, not just visible, and in this way astronomers are able to get a much deeper, multi dimensional understanding of the objects they study.
Light travels in wave form and as you can see in the diagram above, the spectrum of light ranges from very high energy, short wavelength gamma rays at one end of the scale, all the way down to radio waves at the other end of the scale with wavelengths on the scale of several kilometres.
There is a reason why our eyes can only observe visible light – our atmosphere blocks most other electromagnetic wavelengths from reaching the earth's surface! As you can see from this diagram, only visible light and some infrared and radio wavelengths are able to penetrate the earth's atmosphere. Space-based telescopes are necessary to observe all other parts of the EM spectrum.
Even for wavelengths that do penetrate the atmosphere, the sharpness of telescopes' images are severely reduced by water vapour in the air, and by the thickness of the atmosphere – which is why deserts and high mountain-tops are preferred locations for ground-based telescopes.
So what types of information can telescopes at different wavelengths find out? High energy corresponds to violetnt, high speed and high temperature sources, and conversely, low energy light corresponds to a cool heat source.
So for example:
*Gamma rays are emitted from extremly high-energy objects like pulsars, neutron stars and black holes,
*X-rays from hot gasses and the sun's corona
*Ultraviolet from very hot stars and quasars,
*Infra-red from cool stars and dust glowing from absorbed starlight (useful as dust blocks out visible light),
*and radio waves from the Cosmic Background Radiation (energy emitted eons ago, not long after the Big Bang, that has cooled almost to absolute zero travelling through space and time).
When images of a single object at different wavelengths are combined, the results can be startling and revealing. Look at this image of Keplers Supernova remnant - you can see that it is virtually invisible at visible wavelengths, but glows brightly at gamma and ultra-violet wavelengths.
In contrast, this image of the Cartwheel Galaxy shows most energy being emitted at lower energy, cooler wavelengths (visible and infrared) – X-ray emission is very dispersed and doesn't show the galaxy shape at all.
Clearly, there is far far more to the universe than meets the eye!
http://coolcosmos.ipac.caltech.edu/cosmic_classroom/multiwavelength_astronomy/multiwavelength_astronomy/index.html - The EM spectrum and multwavelenth astronomy
1. NASA, ESA, and the Hubble Heritage Team (STScI/AURA)
2. http://imagine.gsfc.nasa.gov/docs/science/know_l1/emspectrum.html
3. http://sci.esa.int/education/34990-wavelength/
4. See bottom of image
5. Chandra, GALEX, Hubble, Spitzer - Composite: NASA/JPL/Caltech/P.Appleton et al.