1. Magnification If a telescope is labelled x50 it tells us the magnification is 50. This means: The telescope will make an object appear 50 times closer The telescope makes the object angular size seem 50 times greater. Magnification = focal length of objective lens/ focal length of eyepiece lens

2. BUT A telescope cannot make stars look bigger because they are too far away. However they can make them look brighter. The aperture ( allows the light in) is bigger than your pupil( lets light into the eye).

3. Problem with converging lenses?

4. Another problem We know that a converging lens………. But white light is made from………… Dispersion is when we …………. This means that a converging lens focuses different colours at slightly different points. If we use a converging lens as the objective lens an unclear image is produced.

5. Galileo’s Telescope Galileo used a diverging lens as the eye piece. A diverging lens is opposite to a converging lens Draw a ray diagram to show this.

6. cont The first design for a reflecting telescope or reflector was just after Galileo’s refracting telescope which used a curved mirror as the objective instead of a lens. The mirror reflects all the colours at the same time. Another advantage is that mirrors can be larger than lens’s which means they can gather more light. A curved mirror is known as parabolic mirror

7. Diffraction We already know that telescopes are able to gather more light due to the size of the aperture. We said that the stars don’t look any bigger through a telescope but they look brighter. The telescope is able to make the gaps between the stars appear bigger. This is due to DIFFRACTION (?????) As light goes through the aperture it diffracts, the larger the aperture the less diffraction there is. We say the larger aperture has a greater resolving power.

8. To avoid diffraction astronomers design telescopes with apertures much larger than the wavelength of the radiation they want to gather. Which telescopes have the largest apertures?

9. Other things taken into consideration with telescopes? Mountings. Which effects ….. Temperature. Things contract and expand Size Position How do you decide where to put your telescope? It depends on the radiation used. Visible, Microwaves and Radio can pass through the atmosphere WITHOUT being absorbed so can be used from Earth. Other radiations are absorbed so the telescope is put into space above the atmosphere. Light pollution.

10. Electronic Imaging Storage Processing Sharing information All of these are made easier since the electronic age has developed. Sharing work improves knowledge and saves money.

11. Explain why an XMM telescope as to be put into space where as a radio telescope such as Jodrell Bank can work from Earth 2 marks