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Chapter 3
Stars
3A-1
Gnomon – a pole, column of stones, pillar,
or pyramid (like a crude clock or calendar)
Uses:
-Tell time of day (movement of shadow)
-Tell time of year (by length of shadow)
-Show motion of heavenly bodies
3A-2 Refractor Telescopes
•Use lenses
•Objective lens refracts (bends) light
•Ocular or eye piece lens focuses &
magnifies image
3A-2 Refractor Telescopes
Functions of a Telescope
1. Light gathering
2. Magnification: make it bigger
3. Resolution: make it clearer
*many stars seen with naked eye are
actually 2 or more stars
Chromatic Aberration
Color distortion due to
using lenses to refract light
Happens because
different wavelengths of
light bend different
amounts and focus on
different points
Chromatic Aberration Solutions
Use very thin lenses that
don’t bend light much
(makes telescope very
long)
Use a compound lens
(one convex & one
concave) cemented
together
Chromatic Aberration
 Sir Isaac Newton
discovered white light is
made of many colors
(each with a different
wavelength)
 His solutions was to use
mirrors instead of lenses
Homework: SRQ 3A-1
BELL WORK
•What is a gnomer?
* Please answer
this question in
your own words
(Don’t just copy a
definition from
your notes.)
3A-3 Reflecting Telescopes
•Developed by Newton
•Use mirrors
•Ex: Newtonian Reflector &
Cassegranian Reflector
3A-3 Newtonian Reflector
•Has concave mirror,
flat mirror, & eye
piece
•Image is viewed
from the side
3A-3 Cassegranian Reflector
Light enters,
reflects off large
concave mirror with
hole in center
Reflects to a
convex mirror, which
reflects through the
hole to the ocular
Advantage:
compact
design
Mirrors & Telescopes
Telescopes with mirrors can be
built much larger than lenstelescopes
- Some 10 m in diameter!
- No aberration if shaped in
parabolic curve
Mirrors & Telescopes
3 Advances in Mirror Design
(made mirrors larger than 5 m possible)
1. Honeycomb mirror – reduces
mirror weight by spincasting
2. Segmented mirrors – smaller
pieces fit together to make large
mirror
3. Meniscus mirror – very thin &
controlled shape by computerized
actuators
Composite Telescope
Uses mirrors & correcting lens objective
Gives fine detail over a wide field
- Ex: Schmidt
telescope
*Be able to diagram all 4 types of
telescopes in 3A-2 & 3A-3
3A-4 Non optical telescopes
•Do not use visible light
•Study other waves given off by stars
(Radiowaves, infra red, ultra violet, gamma & x
rays)
• Atmosphere blocks most of these, but does
not block radio waves
Non optical telescopes
•Radio telescope:
- Has large, dish shaped antenna
- focuses amplifies & analyzes radio waves
from space
- Can send radio waves (as radar)
- Separate radio telescopes can work
together
Non optical telescopes
Other telescopes
*placed above earth & can see
things filtered out by atmosphere
Chandra x-ray telescope
Hubble Space Telescope (HTS)
Placed in orbit in 1990, has optical & non optical
equipment
Can “see” things hidden
behind dust, takes pictures,
transmits them to earth
Telescope Mounts
• Must be able to move vertically &
horizontally to point in any direction
• Altazimuth mount: has separate vertical &
horizontal controls
• Equatorial (German) mount: Telescope tube
rotates around attached pole, pole points to
celestial pole
• Dobsonian mount: useful for amateurs, has a
turn table on the ground and is a modified
Altazimuth
Recording telescope images
• Optical telescope: Image recorded by camera &
photographs
• Non-optical telescope: Computer turns strip
chart/digital data into picture
• Main star charts & catalogs
• 1. hipparchus catalog
• 2. Tycho-2 catalog (2.5 mil. stars)
Keeping track of star data
•Main star charts & catalogs
•1. Hipparchus catalog
•2. Tycho-2 catalog (2.5 mil. stars)
Homework: SRQ 3A-2 (all)
SRQ 3A-3 (1-6)
Study for Quiz 3A