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First Light: Photography & Astronomy Introduction to Spectroscopy

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

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First Light: Photography & Astronomy Introduction to Spectroscopy

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  1. First Light: Photography & Astronomy Introduction to Spectroscopy Christopher G. De Pree Agnes Scott College RARE CATS, June 20, 2002

  2. 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

  3. 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

  4. 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

  5. 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

  6. 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)

  7. Impact on our Understanding • What’s out there? • What is it made of? • How is it moving with respect to us?

  8. 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)

  9. 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)

  10. Telescope Designs • Cassegrain • Coude • Herschelian (obsolete) • Newtonian

  11. 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)

  12. Impact on astronomy (Imaging) • Images create archives • Classification of galaxies • Classification of stars (spectroscopy) • Deep images show detail

  13. Images taken over time • Look for change in successive images • Variable stars • New planets • Asteroids and comets

  14. Spectroscopy • Pass light through a prism • Elemental fingerprints • Why are spectra unique • Electrons “hopping”

  15. Where do spectral lines come from? • Electrons “hopping around” • Molecules spinning and vibrating

  16. Doppler Shift • Motion of the Source • Train whistle • Water waves and ducks • Light experiences the same effect • Redshift--longer wavelength • Blueshift--shorter wavelength

  17. Planetary Detection

  18. Known Extrasolar Planetary Systems

  19. 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

  20. 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

  21. 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

  22. 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

  23. 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

  24. 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)

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