18.2 Telescopes

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Transcript 18.2 Telescopes

Chapter 18.2
Invention of the Telescope
• Definition
An instrument that gathers
electromagnetic radiation from objects in
space and concentrates it for better
Optical Telescopes
• The most common type of telescope.
• Collects and focuses visible light for closer
• Focal Point:
– Point where the rays of light converge in the
• Simplest Telescope has two lenses:
– Objective lens- collects light and forms image
at the back of telescope
– Eyepiece lens- magnifies the image
Refracting Telescope
• Definition:
– 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
– Distorts images if lenses are too large
because the glass sags under its own weight
Refracting Telescopes
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)
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!
How Telescopes Work
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
• On Earth- top of mountain is good location
for telescope because of thinner air
• Best place- Space because no
atmosphere to interfere with light
Electromagnetic Spectrum
• All of the wavelengths of electromagnetic radiation
Visible portion
Electromagnetic Radiation
Nonoptical Telescopes
• Detect radiation that
is not visible.
• Example- Radio
Telescope is much
larger because radio
wavelengths are
• Many nonoptical
telescopes are put in
space because
wavelengths are
blocked by
The Lovell Radio Telescope.
The Hubble Telescope
• Read p. 558 – 563
• Questions p. 563 (in your notebook)
• Show me your answers when finished, so I
can put them in the gradebook.