why do we use telescopes?
Telescopes magnify the image so we get a more detailed view of the object we are observing.
If a telescope has a magnifiaction of 50, it makes the object look 50 times larger.
What are lenses?
Lenses are used to form the image in telescope.
Lenses are usually made from glass. Light entering the glass slows down so it changes direction- this is called Refraction.
when light leaves the glass it speeds up again. It bends the other way.
Measuring the focal length.
The distance between the lens and the focal point is the Focal length.
Why are telescopes so big?
Large telescopes are needed to collect the weak radiation from faint or very distant galaxies. The larger the aperture the brighter the final image will be.
The aperture has to be much larger than the wavelength of the radiation coming from faint or very distant sources, Otherwise diffraction will spread the starlight out and the image will be blurred, not sharp. Radio waves have large wavelengths so these telescopes have be very big.
The resolving power of a telescope measures how well it can distinguish stars that appear close together. It depends on both the aperture size and the wavelength used.
Computers and telescopes.
Computers in telescopes enable astronomers to track and follow a distant star as the Earth rotates.
Computers allow images to be analysed or enhanced. E.g. reduce noise, improve contrast, add false colour) .
Computers allow hundreds of astronomers all over the world to share the same telescope.
Where are telescopes located.
Jodrell bank radio telescope: Cheshire UK.
Arecibo radio telescope: Puerto Rico.
Calar Alto Telescopes: Spain.
European southern observatory: Atacama desert, Chile.
Choosing a location for a telescope.
- A mountainous locating reduces effects of atmosphere which distorts images due to refraction.
- Needs to be remote to avoid light pollution.
- Good number of clear nights.
- Cost, including travel to and from telescope for supplies and workers.
- Environmental and social impact of the project.
- Working conditions for employees.
Telescopes in space.
Telescopes on Earth are effected by:
- The atmosphere which absorbs most infrared, X-ray and gamma radiation.
- Atmospheric refraction which distorts images.
- light pollution.
- Bad weather.
These problems can be overcome by placing the telescope in space where there is no atmosphere, light pollution or bad weather. The Hubble space telescope has a better resolution than any telescope on Earth.
There are also some disadvantages of space telescopes. Mainly the high costs of setting up, maintaining and repairing the telescope. There are also size limitations.
International cooperation Allows high costs to be shared. It also allows expertise to be pooled.
For example 13 different countries have collaborated to run the European southern observatory, which has a number of different telescopes over Chile. Over 1000 different astronomers from around the world use this telescope every year.