1. Chapter 18.2
Telescopes

2. Invention of the Telescope

3. Telescopes Definition
An instrument that gathers electromagnetic radiation from objects in space and concentrates it for better observation.

4. Optical Telescopes The most common type of telescope.
Collects and focuses visible light for closer observation.
Focal Point:
Point where the rays of light converge in the telescope.
Simplest Telescope has two lenses:
Objective lens- collects light and forms image at the back of telescope
Eyepiece lens- magnifies the image

5. Refracting Telescope Definition: Disadvantages:
Uses a set of lenses to gather and focus light from distant objects
Disadvantages:
Cannot focus images perfectly because lenses focus different colors at different distances
Distorts images if lenses are too large because the glass sags under its own weight

6. Refracting Telescopes

7. Reflecting Telescope Definition:
Uses a curved mirror to gather and focus light from distant objects
Used by most professional astronomers b/c:
Mirrors can be very large (gather more light)
Mirrors are polished (flaws don’t affect light)
All colors of light focus to same point (all colors seen in focus at same time)

8. Reflecting Telescope
Reflecting telescopes use curved mirrors instead of convex lenses to collect and focus light. A large concave mirror (the center is thinner than the edges) collects and reflects the light to make an image. Once the image forms, the lens in the eyepiece magnifies the image. Reflecting telescopes are very helpful for viewing dim or dark objects. Large reflecting telescopes can see objects that are a millionth or a billionth the brightness of the faintest star that can be seen by the human eye alone!

9. How Telescopes Work

10. The Atmosphere “Twinkle, Twinkle Little Star”
Stars don’t “twinkle”- the atmosphere causes starlight to shimmer and blur and look like it’s twinkling
Light gathered by telescopes on the Earth’s surface is affected by the atmosphere
On Earth- top of mountain is good location for telescope because of thinner air
Best place- Space because no atmosphere to interfere with light

11. Electromagnetic Spectrum
All of the wavelengths of electromagnetic radiation
Invisible Invisible
ROYGBIV
Visible portion
LONG
SHORT

12. Electromagnetic Radiation

13. Nonoptical Telescopes
Detect radiation that is not visible.
Example- Radio Telescope is much larger because radio wavelengths are longer.
Many nonoptical telescopes are put in space because wavelengths are blocked by atmosphere.
The Lovell Radio Telescope.

14. The Hubble Telescope

15. Read p. 558 – 563
Questions p. 563 (in your notebook)
Show me your answers when finished, so I can put them in the gradebook.