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Explore the rich history of astronomical instruments from ancient visual observations to modern telescopes. Learn about the anatomy and detection characteristics of the human eye, navigation techniques, calendars, and observations of unusual objects like comets. Delve into the Hawaiian navigation methods and the Tycho Quadrant pre-telescopic observations. Discover why telescopes were built, the advantages of larger apertures, and the differences between refractor and reflector telescopes. Explore key figures like William Herschel and the Herschel 40-ft Telescope, along with basic optical designs like the prime focus and Newtonian telescopes. Understand the mirror grinding and polishing processes, and the challenges of ground-based observations due to diffraction and atmospheric turbulence. Learn about modern observatories like the ESO-VLT Observatory in Chile and the characteristics of optimal observation sites.
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History of Astronomical Instruments The early history: From the unaided eye to telescopes
The Human Eye Anatomy and Detection Characteristics
Visual Observations • Navigation • Calendars • Unusual Objects (comets etc.)
Hawaiian Navigation: From Tahiti to Hawaii Using the North direction, Knowledge of the lattitude, And the predominant direction of the Trade Winds
Pre-Telescopic Observations • Navigation • Calendar • Astrology • Planetary Motion • Copernican System • Kepler’s Laws
Why build telescopes? • Larger aperture means more light gathering power • sensitivity goes like D2, where D is diameter of main light collecting element (e.g., primary mirror) • Larger aperture means better angular resolution • resolution goes like lambda/D, where lambda is wavelength and D is diameter of mirror
Refractor telescopes exclusively use lenses to collect light have big disadvantages: aberrations & sheer weight of lenses Reflector telescopes use mirrors to collect light relatively free of aberrations mirror fabrication techniques steadily improving Collection: Telescopes
William Herschel Caroline Herschel
Basic optical designs: Prime focus: light is brought to focus by primary mirror, without further deflection Newtonian: use flat, diagonal secondary mirror to deflect light out side of tube Cassegrain: use convex secondary mirror to reflect light back through hole in primary Nasmyth focus: use tertiary mirror to redirect light to external instruments Optical Reflecting Telescopes
Drawing of the Moon (1865)
The Limitations of Ground-based Observations Diffraction Seeing Sky Backgrounds
Characteristics of Good Sites • Geographic latitude 15° - 35° • Near the coast or isolated mountain • Away from large cities • High mountain • Reasonable logistics
Modern Observatories The ESO-VLT Observatory at Paranal, Chile