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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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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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 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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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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H-band OH Emission Lines
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Camera Construction Techniques 1.
The photo below shows a scientific CCD camera in
use at the Isaac Newton Group. It is
approximately 50cm long, weighs about 10Kg and
contains a single cryogenically cooled CCD. The
camera is general purpose detector with a
universal face-plate for attachment to
various telescope ports.
Pre-amplifier
Vacuum pump port
Pressure Vessel
Mounting clamp
Camera mounting Face-plate.
Liquid Nitrogen fill port
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Camera Construction Techniques 4.
A cutaway diagram of the same camera is shown
below.
Thermally Electrical feed-through Vacuum
Space Pressure vessel Pump
Port Insulating Pillars
Face-plate
.
.
Telescope beam
Boil-off
.
Optical window CCD CCD Mounting
Block Thermal coupling Nitrogen can
Activated charcoal Getter
Focal Plane of Telescope
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Camera Construction Techniques 5.
The camera with the face-plate removed is shown
below
Retaining clamp
Temperature servo circuit board
CCD
Aluminised Mylar sheet
Gold plated copper mounting block
Top of LN2 can
Platinum resistance thermometer
Pressure Vessel
Spider. The CCD mounting block is stood off
from the spider using insulating pillars.
Location points (x3) for insulating pillars that
reference the CCD to the camera face-plate
Signal wires to CCD
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Camera Construction Techniques 6.
A Radiation Shield is then screwed down onto
the spider , covering the cold components but not
obstructing the CCD view. This shield is highly
polished and cooled to an intermediate
temperature by a copper braid that connects it to
the LN2 can.
Radiation Shield
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Camera Construction Techniques 7.
Some CCDs cameras are embedded into optical
instruments as dedicated detectors. The CCD shown
below is mounted in a spider assembly and placed
at the focus of a Schmidt camera.
CCD Signal connector (x3)
Copper rod or cold finger used to cool the CCD.
It is connected to an LN2 can.
Spider Vane
CCD Clamp plate
Gold plated copper CCD mounting block.
FOS 1 Spectrograph
CCD Package