Transcript Astronomical Tools

Astronomical Tools
Essential Questions
1. What is Light?
2. How do telescopes work, and how are
they limited?
3. What kind of instruments do
astronomers use to record and
analyze light?
4. Why do astronomers use radio
telescopes?
5. Why must some telescopes go into
orbit?
A particle and a wave…
• Electromagnetic radiation comes in many
types but all have the same speed.
• Speed = frequency x wavelength (c = f x λ)
• Particles of light are called photons.
Light
• Light is the visible form of
electromagnetic radiation.
• It’s an electric and magnetic
disturbance that transports energy at
the speed of light.
• The EM Spectrum includes: Radio,
Microwave, Infrared, Visible,
Ultraviolet, X-Rays, and Gamma Rays.
• A photon, or particle of light, can be
thought of as a bundle of waves that
sometimes acts like a wave and
sometimes like a particle.
Visible Light
• The visible spectrum
ranges from 700 nm
red light to 400 nm
violet light.
• ROY G BIV
• As wavelengths
decrease, energy
increases.
• As frequency
increases so does
energy.
Try a few calculations…
• Find the frequency of red light
(λ = 700 x 10-9 m)
• Find the frequency of violet light
(λ = 400 x 10-9 m)
• Find the wavelength of your favorite
radio station… (remember M = mega
or 106)
Telescopes
• Earth based or
space based,
telescopes are
designed to do
one thing very
well…
• Gather and
focus as much
light as
possible.
Bigger is Better
• Telescopes allow
astronomers to
gather light, see fine
detail, and magnify
images.
• The first two depend
on the telescope’s
diameter or aperture.
• Consequently,
astronomers always
strive for larger
scopes.
Reflectors use Mirrors
Refractors use Lenses
Both reflectors and refractors
use lenses in the eyepiece.
Refracting Telescopes
• A refracting telescope uses a lens to
gather and focus light.
• Because of chromatic aberration,
refractors cannot bring all colors to
focus at the same spot—color fringes
result.
• An achromatic lens partially corrects
for this, but such lenses are
expensive.
• Refracting lenses cannot be made
larger than 1 meter—they warp if too
heavy.
Chromatic Aberration
Yerkes Refractor
• The world’s largest
refracting telescope
is located in
Wisconsin.
• The diameter of the
lens is 40 inches.
• Any more than this,
and the lens will
warp and change
shape due to its own
weight.
Reflecting Telescopes
• Use a mirror to gather and focus
light.
• Less expensive than refractors of
the same diameter.
• Do not suffer from chromatic
aberration.
• Most recently built large telescopes
are reflectors.
• The mirror can be supported from
below, so there is no limit to size
(except for $).
The Keck Observatory
• The world’s largest
reflecting telescopes
are the twin Keck
reflectors in Hawaii.
• Each scope has a 10
meter diameter mirror!
• Actually a group of
segmented mirrors put
together.
Types of Reflectors
Types of Reflectors
• Prime focus—instruments/eyepiece on the
light gathering end of scope.
• Newtonian Focus—instruments/eyepiece
on side of scope, a secondary mirror
bounces light out the side.
• Cassegrain Focus—instruments/eyepiece
behind the primary mirror, light enters
through a hole in the primary.
Observatories on Mountains
WIRO 2004
Telescopes High and Dry
• Astronomers build observatories
on mountains for two reasons:
• Better “seeing” due to less
turbulence in the atmosphere.
• Air is thinner and dryer and is
therefore more transparent
especially to infrared.
• After all, WIRO—Wyoming
Infrared Observatory
Advances in Optical Telescopes
• Sometimes
telescopes are
linked through a
technique called
interferometry.
• Resolution is equal
to the separation of
the two scopes.
• Adaptive optics
have also been used
to compensate for
atmospheric
distortion.
Modern Instruments
• For many years astronomers used
photographic plates to record images at
the telescope.
• Modern electronic systems such as
CCDs (advanced digital camera chips)
have replaced most photographic
plates.
WIRO Camera and Control
Spectrographs
• Spectrographs using prisms or a grating spread
starlight out according to wavelength.
• This reveals a spectrum showing hundreds of
spectral lines produced by atoms in the object
being studied.
Radio Astronomy
• Astronomers use
radio telescopes
for three reasons:
1. Can detect cool
hydrogen
2. Can see through
dust clouds
3. Can detect
objects invisible
at other
wavelengths
Radio astronomy details
• Radio telescopes can be used during
the day
• Consist of a dish reflector, an antenna,
an amplifier and a data recorder.
• The largest single, fully-steerable,
radio telescope is in Green Bank, WV.
(100 m)
• The largest single radio telescope is
located in Puerto Rico and at Arecibo.
(300 m) Maybe you’ve seen it in a 007
movie…
Arecibo Radio Telescope
Radio Interferometry
• Radio telescopes have poor resolution due
to the long wavelength of radio waves.
• Often linked to get better resolution.
• The VLA in New Mexico can be 30 km
across!
Atmospheric Windows
Our troublesome atmosphere
• Although our atmosphere is nice to
breathe and shields us from many
forms of nasty radiation and
meteors…
• It only allows us to use ground
based telescopes in the visible,
radio/microwave, and some
infrared parts of the spectrum.
• For the other wavelengths, we
must go into space…
Space Based Telescopes
• Earth’s atmosphere
absorbs some
radiation and
distorts light that
does get through.
• Telescopes in orbit
avoid this and are
limited only by their
size.
• Some have proposed
lunar observatories!
Multi-wavelength Crab
The Crab Nebula in Radio
The Crab Nebula in Infrared
The Crab Nebula in Visible
Visible Again
The Crab Nebula in Ultraviolet
The Crab Nebula in X-Ray