History of Astronomical Instruments

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History of Astronomical Instruments

• The early history
• From the unaided eye to telescopes

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The Human Eye

• Anatomy and
• Detection Characteristics

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Anatomy of the Human Eye
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Visual Observations

• Navigation
• Calendars
• Unusual Objects (comets etc.)

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Hawaiian Navigation From Tahiti to Hawaii Using
the North direction, Knowledge of the
lattitude, And the predominant direction of the
Trade Winds
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Tycho Quadrant
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Hevelius Sextant
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Hevelius Quadrant
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Pre-Telescopic Observations

• Navigation
• Calendar
• Astrology
• Planetary Motion
• Copernican System
• Keplers Laws

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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

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Collection Telescopes

• 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

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William Herschel
Caroline Herschel
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Herschel 40 ft Telescope
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Optical Reflecting Telescopes

• 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

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Optical Reflecting Telescopes

• Use parabolic, concave primary mirror to collect
  light from source
• modern mirrors for large telescopes are
  lightweight deformable, to optimize image
  quality

3.5 meter WIYN telescope mirror, Kitt Peak,
Arizona
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Mirror Grinding Tool
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Mirror Polishing Machine
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Fine Ground Mirror
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Mirror Polishing
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Figuring the Asphere
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Crossley 36 Reflector
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Yerkes 40-inch Refractor
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Drawing of the Moon (1865)
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First Photograph of the Moon (1865)
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The Limitations of Ground-based Observations

• Diffraction
• Seeing
• Sky Backgrounds

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Diffraction
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Wavefront Description of Optical System
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Wavefronts of Two Well Separated Stars
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When are Two Wavefront Distinguishable ?
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Atmospheric Turbulence
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Characteristics of Good Sites

• Geographic latitude 15 - 35
• Near the coast or isolated mountain
• Away from large cities
• High mountain
• Reasonable logistics

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Modern Observatories
The VLT Observatory at Paranal, Chile
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Modern Observatories
The ESO-VLT Observatory at Paranal, Chile
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Puu Poliahu
UH 0.6-m
UH 2.2-m
UH 0.6-m
The first telescopes on Mauna Kea (1964-1970)
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Local SeeingFlow Pattern Around a Building

• Incoming neutral flow should enter the building
  to contribute to flushing, the height of the
  turbulent ground layer determines the minimum
  height of the apertures.
• Thermal exchanges with the ground by
  re-circulation inside the cavity zone is the main
  source of thermal turbulence in the wake.

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Mirror Seeing

• When a mirror is warmer that the air in an
  undisturbed enclosure, a convective equilibrium
  (full cascade) is reached after 10-15mn. The
  limit on the convective cell size is set by the
  mirror diameter

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LOCAL TURBULENCEMirror Seeing
The contribution to seeing due to turbulence over
the mirror is given by

• The warm mirror seeing varies slowly with the
  thickness of the convective layer reduce height
  by 3 orders of magnitude to divide mirror seeing
  by 4, from 0.5 to 0.12 arcsec/K

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Mirror Seeing
The thickness of the boundary layer over a flat
plate increases with the distance to the edge in
the and with the flow velocity.

• When a mirror is warmer that the air in a flushed
  enclosure, the convective cells cannot reach
  equilibrium. The flushing velocity must be large
  enough so as to decrease significantly (down to
  10-30cm) the thickness turbulence over the whole
  diameter of the mirror.

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Thermal Emission AnalysisVLT Unit Telescope

• UT3 Enclosure
• 19 Feb. 1999
• 0h34 Local Time
• Wind summit ENE, 4m/s
• Air Temp summit 13.8C

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Gemini South Dome
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Coating- thermal properties
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Enclosure coatings

• UKIRT - reflective bare aluminum
• UH - TiO2-based white paint
• GEMINI - Al-based Lo-Mit paint
• CFHT - TiO2-based white paint
• IRTF - reflective aluminum foil
• KECK - TiO2-based white paint
• SUBARU - - reflective Alclad siding

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CFHT
Keck
UKIRT
IfA
Gemini
IRTF
Subaru
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Coatings tested

• red metal primer ACE
• CFHT white paint Triangle Paint Co.
• Gemini aluminum paint Lo-Mit
• IRTF Al foil 3.1mil 3M product 439
• light blue acrylic latex ACE color 24-D
• dark blue acrylic latex ACE color 24-B

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White
Al foil
Lo-Mit
Primer
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Solar spectrum
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Coatings - conclusions

• Paints
• all paints supercool at night by radiating to the
  sky
• white paint heats the least in sunlight
• pigmented paints heat more than white during the
  day
• Reflective coatings
• ideal thermal properties
• heat very little during the day
• hardly supercool at all at night

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Conclusions

• Curved surfaces remain visible over wide areas
  regardless of whether they are painted or
  reflective, and are therefore difficult to hide.
• Flat panels CAN produce very bright glares, but
  only in very specific directions. Outside these
  directions a panel will reflects blue sky.
• The reflection of sunlight from cylindrical
  reflecting surfaces is much brighter than from
  spherical surfaces of similar size.
• White domes and reflective domes in direct
  sunlight are equally bright, but reflective domes
  are visible much longer

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Sunset on Mauna Kea
Keck I and Subaru September 20, 1999
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Conclusions

• Telescope enclosures with both low visibility and
  excellent thermal properties are possible
• A promising approach
• highly reflective siding
• vertical flat walls
• active control of glare geometries
• Domes - painted or reflective are hard to hide
• Reflective domes remain highly visible longer
  than painted domes

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Night Sky Emission Lines at Optical Wavelengths
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Sky Background in J, H, and K Bands
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Sky Background in L and M Band
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V-band sky brightness variations
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J-band OH Emission Lines
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H-band OH Emission Lines
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K-band OH Emission Lines
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Uncorrected
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ADC Conceptual Design

• Linear ADC design
• Variable prism separation provides correction
• UV-to-near IR transmission requires fused silica
  optics

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Fully Open, Z60?
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Corrector for 4m prime focus telescope (parabolic
mirror)
This corrector includes an atmospheric dispersion
compensator consisting of 2 counter-rotating
lenses (doublet)