2. ONE OF THE TWIN KECK TELESCOPES ON THE SUMMIT
OF MAUNA KEA, HAWAII, DURING A TOTAL ECLIPSE OF
THE SUN. THESE ARE THE TWO LARGEST INDIVIDUAL
OPTICAL TELESCOPES IN THE WORLD.
6. 1- COLLECTING POWER
= the amount of light the telescope is
able to focus into the eyepiece
• The more light it collects, the brighter
the image
• Stars will always look like points of
light, but you will be able to see
more (fainter ones) and they will be
brighter
=This is the most significant factor
7.
8. Collecting Power
• Light-collecting ability varies with the square of the
aperture.
• Thus, a 90mm telescope (a little under 4”) collects
only 1/5 as much light as an 8” telescope
9. The larger the diameter of the lens
or mirror used in a telescope:
- The greater its ability to
gather light
- The finer the detail that the
instrument will show
10. Telescopes - Refractors
Use two or more
lens to bend
(refract) the light,
so it focuses on
the eyepiece at
the end of the
telescope.
11.
12. How a lens focuses light
A lens bends (or refracts) the
light and focuses it on a point
13. Telescopes - Reflectors
Gather light at the primary
mirror (curved) on the far end
of the tube, which focuses the
image onto the secondary
mirror (flat), that redirects the
light at a right angle into the
eyepiece, mounted on the side
of the telescope.
14.
15. REFLECTORS:
Also called Newtonian Reflectors
- First designed by Isaac Newton, around 1670
The best light-gathering capability
Quality of mirrors very critical
Good for astronomy viewing only
-They invert the image (objects look
upside down)
16. How a curved mirror focuses light
Mirrors that are made of glass that has been
shaped to a smooth curve, polished and
then coated with a thin layer of aluminum or
some other highly reflective material
19. Why Reflecting Telescopes are
Preferred over Refracting
• A large mirror can be thin but a large
lens must be thicker thus heavier.
• A lens has two surfaces that must be
cleaned and polished; a mirror only has
one
• Glass absorbs light! The thicker the light
the more absorption.
20. • Lenses need to be supported only
around the outside; mirrors can be
supported by the back
• For large lenses, glass deforms under
its own weight; thus changing the
lenses’ properties.
• In a lens, different colors are refracted
by different amounts. (Chromatic
Aberrations). Lenses are corrected for
chromatic aberrations and are called
achromats.
21. Cassegrains telescope
Cassegrains
have a compact
tube which
incorporates
primary and
secondary
mirrors that fold
the light path
and focus the
light into the
eyepiece at the
end of the tube.
22. 2- MAGNIFYING POWER
the number of times a
telescope can increase
the apparent size of an
object.
23.
24. Calculating Magnification
Magnification = Telescope focal length
Eyepiece focal length
Telescope focal length = The distance from the center
of a curved mirror or the center of the lens (where
light passes through the first element of the
telescope) to the focal point.
Orion Catalogue
Orion AstroView Meade LX200R
25. Calculating Magnification
Magnification = Telescope focal length
Eyepiece focal length
Eyepiece focal length = The distance
from the center of the field lens (where
light passes through the first element of
the eyepiece) to the focal point.
• Given in millimeters
26. Magnification = Telescope focal length
Eyepiece focal length
Examples
• 750 mm = 30x
25 mm
3048 mm = 122x
25 mm
OR
750 mm = 100x
7.5mm
3048 mm = 406x
7.5 mm
27. 3. Resolving Power
• Resolving Power = the ability of the
instrument to discriminate fine detail.
• How sharp or fuzzy the image is
• The limitation on resolving power is imposed by
the interaction of light and optics.
• The quality of the optics is a major factor
• Lens, mirrors, eyepieces, etc.
• Usually, you get what you pay for
• The turbulence in the air column you are
looking through, moisture in the air, etc. also
effect this.
29. The Earth’s atmosphere
interferes seriously with
observing.
It absorbs and totally blocks
many wavelengths.
It blurs details.
Interferometers enhanced the resolving power
in sources.
30. Astronomers use special-
purpose telescopes to
observe non-visible
wavelengths. Many of
these are in orbit, so they
are not affected by blurring
or atmospheric absorption.
31. “The Hubble Space Telescope orbits far above the
distorting effects of the atmosphere, about 600
kilometers above the Earth. This perch gives
astronomers with their clearest view ever, but it
also prevents them from looking directly through
the telescope. Instead, astronomers use Hubble's
scientific instruments as their electronic eyes.”
Upper Left: Closer View
32. “This color image
of Saturn was
taken with the
HST's Wide Field
and Planetary
Camera (WF/PC)
in the wide field
mode at 8:25
A.M. EDT, August
26, 1990, when
the planet was at
a distance of 1.39
billion kilometers
(860 million
miles) from
Earth.”
Credit for picture and text: NASA
33. “This enlargement
of the Saturn
image reveals
unprecedented
detail in
atmospheric
features at the
northern polar
hood. Saturn's
north pole is
presently tilted
toward Earth by
24 degrees”
Courtesy for
picture and text:
NASA
34. View of a colliding galaxy dubbed the "Tadpole" (UGC10214):
Photo Courtesy NASA Hubble
35. Telescopes – Eyepieces
• An eyepiece brings
the light rays
gathered by the
telescope into sharp
focus.
• The eyepiece
determines the
magnification, as
well as its
brightness and
contrast
Your eye
36. Telescopes – Eye Relief
• Eye Relief is the
distance between
the eyepiece lens
and your eye,
when the image is
in focus
• Eyeglass
wearers need at
least 15mm
37. Telescopes – Eye Relief
• Shorter focal-length
eyepieces tend to have
shorter eye relief than
longer focal length
eyepieces.
• Smaller lens openings
• You need to get closer
to them to see the
image
• Like looking through a
peek-hole. 17mm 6 mm
NightWatch, p. 76
38. Telescopes – Finder scopes
• Finder scopes are
miniature telescopes
mounted parallel to
the main tube that
allow easy alignment
of the target object.
• Object is centered in
the crosshairs of
finder scope
• Has to be adjusted
to the main
telescope
NightWatch, p. 67
Finder scopeEyepiece
39. Telescopes – Tripods/Mounts
• A sturdy tripod and mount are essential
to jiggle-free viewing
• Especially at higher magnifications
• The slightest movement is greatly
magnified
• The mount also has to be able to
smoothly adjust for the Earth’s rotation
• Especially at higher magnifications
• The objects move quickly through
the field of view
41. Accessories
• “Go to” computer
controllers
• A computer is built
into the telescope
base
• Once the computer
is aligned, the
system is able to
find thousands of
celestial objects
www.meade.com
42. Accessories
• Filters
• Moon – too bright when more than
half the moon is lighted
• Planets – different colors enhance
the image
• Sun – large filter that goes over the
front opening
•Otherwise, you could “cook” the
inside of the telescope
