Optical Telescope Notes (parts of topic 2 and 4)

When studying celestial bodies, we have always been restricted because of how far we are able to see. Telescopes were invented to allow us to magnify objects at great distances.A simple telescope uses two lenses in order to operate:

Resolving Power (p. 370)

-Resolving power is the __________________________________________________________________________________________________

-What results in a stronger resolving power? Why? __________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________.

Calculating Magnification Your telescope's main tube (objective) has a "focal length", which is essentially the distance the light travels from the first lens or mirror to the eyepiece. It's usually measured in millimeters, and a number like 1000mm is common. It will be specified in your telescope's manual and may be marked on the lens.

You also put an eyepiece (ocular lens) in your telescope, and the eyepiece also has a focal length. It will be clearly marked on the end or the side of the eyepiece. Numbers between 3mm and 30mm are common for eyepieces.

Magnification = telescope (objective) focal length eyepiece focal length

So, in the examples shown in these photos, a 816mm telescope fitted with a 25mm eyepiece gives a magnification of: 816 / 25 = 33 power.

Calculate the magnification if we replaced the eyepiece with a 4mm eyepiece in the same telescope. (Show the formula, substitution and answer in the space below.)

As you can see, any telescope can be made to produce any magnification just by mixing eyepieces. However, there is a limit to the amount of magnification a given telescope can usefully provide. Beyond this limit, the image will be blurry -- like trying to zoom in a digital photo beyond what the resolution of the camera supports. As magnification increases, you need more light. A telescope's light gathering power is directly related to the diameter (or aperture) of the objective lens or mirror. The larger the lens is, the more light the telescope can collect.

ocular lens

objective lens

3 Types of Telescopes 1. Refracting Telescope: (Dioptrics) which use lenses Better images than equal sized reflectors Could not focus different colours in the same place

2. Reflecting Telescope: (Catoptrics) which use mirrors Can be made much larger Mirrors can focus different colours in the same place

3. Combination Telescope: (Catadioptrics) which use lenses and mirrors in combination

Most telescope designs produce an inverted image.

**Do topic 2 review p. 374 #4 & 5.

In 1773, using newer and larger telescopes, astronomers were able to discover __________________(p. 385).

Combining Telescopes (p. 385)

Newer telescopes use _______________________________ which can take images from two or more telescopes and

_________________________________________. This creates the equivalent of one telescope -_________________________________________________________________________________________________________________________________.

Adaptive Optics (p. 386)

The stars twinkle because ________________________________________________________________________________________________ (think of looking through slow moving water at a pebble – the image of the pebble tends to wobble)

In order to get a clear picture of objects in space astronomers need to get rid of the twinkle effectThere are three ways to do this:

E.g. The Keck Telescope in Hawaii. Combing their images together has a resolving power that is able to distinguish each headlight on a car 800km away!

1. ______________________________________________ (e.g. Hubble) - then we don’t have to worry about the distortion caused by the moving atmosphere

2. ______________________ (e.g. NTT New Technology Telescope) -is called this because the computers that control the image you see are always adapting the mirror to changes in Earth's atmosphere. A laser is used to read the movement of the atmosphere and computers adjust small motors behind the mirror to distort the lenses shape to cancel out the distortion. (Think of it like a pair of glasses that automatically adjusts to person’s prescription when they put them on.)

3. Computer software can also be used to cancel out the effects of the distortion if the program knows the speed and movement of the atmosphere at the time the picture was taken. This lessens the cost of expensive lenses and mirrors for older telescopes.