Astronomy 1010-H
Planetary Astronomy
Fall_2015
Day-23
Course Announcements
•
How is the sunset/sunrise observing going?
•
SW-chapter 6 posted: due Fri. Oct. 23
•
1st Quarter Observing night: Tuesday, Oct. 20; 7:30pm
 Electronic detectors record photons on pixels.
 Photons create a signal in the array.
 CCDs = charge-coupled devices (such as
digital cameras).
 The electronically recorded images can greatly
exceed photographs in quality.
 CCD = astronomer’s detector of choice.
Red
Green
Blue
Red
Green
Blue
Color separation is useful in a
prism so that we can obtain a
spectrum of light
Since it is meant to
be separated we
don’t call it an
aberration.
Instead, it is called
dispersion
 Spectrographs disperse the incoming light
into its component wavelengths.
 Lets astronomers study the spectrum of an
object’s light.
A diffraction grating works on
interference of light waves
Diffraction is much
more efficient at
separating light
into its colors than
dispersion
Unfortunately, diffraction
also leads to problems
Look closely enough at stars and they aren’t just
points of light but rings, too
The best spectrographs use
diffraction gratings
The spectrograph/CCD produces a
black & white spectrum
Multitasking Saves Time
Spectrum
But visible light is
only one type of
electromagnetic
radiation (light)
emitted by stars
Astronomers are
truly interested in
the entire spectrum
of Light!
 The atmosphere does not transmit all light.
 Nearly all X-ray, ultraviolet, and infrared
wavelengths are blocked.
 Satellites are needed for these wavelengths.
Consider This Class as Seen in Different
Wavelengths of Light!
Orion in Infrared!
HST Views of Orion Nebula showing
stars hidden in clouds
http://oposite.stsci.edu/pubinfo/pr/97/13/A.html
Observations at other wavelengths are
revealing previously invisible sights
UV
Infrared
Ordinary
visible
Map of
Orion
region
 Radio telescopes are large, steerable
parabolic dishes with antennas.
 Allow astronomers to study radio waves.
 Wavelengths of a centimeter to about 10
meters.
 Radio waves can pass through gas and dust.
Radio wavelength observations are
possible from Earth’s surface
Observing with Radio Waves
Long Wavelength…poor resolution
Under the dish at Arecibo
The Very Large Array (VLA)
 Single radio telescopes have poor resolution
due to the long wavelengths.
 Interferometric arrays combine the signals
from many telescopes, increasing resolution.
CONNECTIONS 6.2
 Two electromagnetic waves in the same
location will produce interference.
 The waves will either enhance or detract from
each other, resulting in constructive or
destructive interference.
 This can result in spectral dispersion.