Photography & Astronomy Introduction to Spectroscopy Christopher G. De Pree Agnes Scott College RARE CATS, June 20, 2002
Dec 21, 2015
First Light: Photography & Astronomy Introduction to Spectroscopy
Christopher G. De Pree
Agnes Scott College
RARE CATS, June 20, 2002
Overview
Advent of Photography Applications of photography in
astronomy Imaging Spectroscopy
Early pioneers in astrophotography Harvard College Observatory Annie Cannon
Impact on our understanding of the universe
Advent of photography
“Camera” from camera obscura, Latin for “dark room”
Drawing by Gemma Frisius De Radio Astronomica et Geometrica
(1545) Thomas Wedgwood (1771-1805) and Sir
Humphry Davis Late 18th century first photographic
images Photosensitivity of silver nitrate and silver
chloride
Daguerreotypes
1831 French painter Louis Jacques Mandé Daguerre
Photographs on silver plates Coated with a light-sensitive layer of
silver iodide Permanent photographs
Developed plate was coated with a strong solution of table salt
Daguerre method produced a single image on the silver plate
Evolution of the Form British inventor William Henry Fox
Talbot photographic method involving the use
of a paper negative Calotype process (30 sec exp.)--
multiple prints Daguerre and Talbot announced
processes in 1839 Within three years the exposure time in
both processes was a few seconds
Applications in Astronomy Imaging
Long exposure times--faint objects Tracking single objects Long time-scale monitoring
Spectroscopy Emission mechanisms Identifying elements
Helium in the solar spectrum Relative motions (Doppler Shift)
Impact on our Understanding What’s out there? What is it made of? How is it moving with respect to
us?
Imaging
Development of “fast” film Problem of first photographic
techniques (no smiles) Rotation of the Earth Exposure times of a few minutes
Long exposure times Detect faint sources Tracking required Telescope stability (mounts)
Tracking
Equatorial Mount Moves to counteract Earth’s
Rotation Must be “polar aligned”
Altazimuth mount Not a unique coordinate system More difficult to track
Some modern telescopes use (e.g. VLA, VLBA)
Telescope Designs
Cassegrain Coude Herschelian (obsolete) Newtonian
Beck Telescope
30” diameter primary mirror Cassegrain or Newtonian
arrangement German equatorial mount Counterbalance Tracking system (clock drive)
Mechanical (1930) Electrical (1966) Computer-controlled (1998)
Impact on astronomy (Imaging) Images create archives
Classification of galaxies Classification of stars
(spectroscopy) Deep images show detail
Images taken over time
Look for change in successive images Variable stars New planets Asteroids and comets
Spectroscopy
Pass light through a prism Elemental fingerprints
Why are spectra unique Electrons “hopping”
Where do spectral lines come from? Electrons “hopping around” Molecules spinning and vibrating
Doppler Shift
Motion of the Source Train whistle Water waves and ducks Light experiences the same effect
Redshift--longer wavelength Blueshift--shorter wavelength
Planetary Detection
Known Extrasolar Planetary Systems
Use of Stellar Spectra
Harvard College Observatory Edward Pickering “Computers”
Antonia Maury(1866-1952) Classification scheme Position and width of absorption lines
Annie Cannon (1863-1941) Established the current stellar
classification scheme
Luminosity Classification (Maury) Absorption lines are pressure-sensitive
Lines get broader as the pressure increases.
Giant stars are puffier, which means lower pressure
Giant stars have narrower absorption lines
Supergiant stars have absorption lines that are even narrower
Used by Ejnar Hertsprung
Temperature Classification (Cannon) Harvard system (HD catalog)
Classifying stars by their spectra Spectral classification by surface
temperature Systematic work on all stars down to
9th magnitude Used photographic plates (16x fainter
than human eye sees) Cannon could identify spectral
patterns at 3 stars/minute
Cannon’s Contributions
Most stars grouped into a small number of classes
Personally classified spectra for more than 225,300 stars Henry Draper Catalogue
Discovered more than 300 variable stars and five novae
Conclusions
Significant advances in astronomy followed the advent of photography Deep imaging
Classification of galaxies Archiving
Time variability of stars Discovery of planets, comets,
asteroids
Conclusions (cont.)
Stellar spectroscopy Classification scheme Understanding of how stars evolve Motion (Doppler Shift)
• Extrasolar planets
Spectroscopy in general• Rotation of galaxes• Expansion of the universe
The next great leap Charge Coupled Devices (CCDs)