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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Rod Cells in a Fish Retina
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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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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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0.6 arcsec
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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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The Galactic Center Discovery Strip Chart
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The Galactic Center Becklin Neugebauer 1975
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The Galactic Center Forrest et al. 1986
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The Galactic Center Rigaut et al. 1997
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The Galactic Center Recent ESO Results
Zeroing in on a Massive Black Hole
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Summary

• Survey conducted world-wide to develop a snap
  shot of instrumentation used today and planned
  for tomorrow
• Intent is to use this database to
• Explore where we are now in astronomy
• Extrapolate to the future
• Help bridge gap between astronomical community
  and manufacturers about what types of detectors
  are needed
• Not intended to be a detailed description of any
  institutions instruments
• No single observatory is large enough to
  dominate the database

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Survey Details

• Instrument name
• Observing Modes
• Start of operations
• Wavelength Coverage
• Field of View
• Instrument cost
• Multiplex gain
• Spatial /Spectral resolution
• Detectors
• Detector Format
• Detector size

• Buttability
• Pixel size
• Pixel scale
• Electronics
• Noise
• Readout Time
• Dark Current
• Full well
• Cost per pixel
• Comments or additional parameters

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Survey Details

• 25 institutions polled as part of a world-wide
  survey of ground-based instrumentation
• Compiled instrumentation database for telescopes
  with ?3.5 m aperture
• Compiled data on 200 instruments through this
  survey
• Enough to probe various trends in instrumentation
  and the detector systems in use today at major
  astronomy facilities, worldwide
• Detailed results will be published via the
  Proceedings of this conference
• Represents a unique source of information about
  instrumentation in astronomy, both existing and
  planned

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Wavelength Coverage

• The great divide between optical and infrared
  is obvious
• Basically a bimodal distribution, separated at 1
  µm
• This divide is artificial - its technology
  driven, not science driven

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Optical, Near-Infrared, or Mid-Infrared?

• Currently astronomy is pretty heavily dominated
  by optical instruments, with 2 out of 3
  instruments using CCDs

• The next-generation of instruments will consist
  of nearly equal numbers of optical and NIR
  instruments

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Optical, Near-Infrared, or Mid-Infrared?

• In both cases MIR instruments occupy a very small
  part of the market
• This is due to many reasons including
• A relatively small MIR community
• A historically specialized field technically to
  get into
• The need for special telescope systems
  (chopping), etc.
• The lack of MIR instruments reflects a relatively
  untapped science frontier, not lack of
  scientific importance

NOW
FUTURE
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What Modes are Most Commonly Used?

• Spectrometers remain the most popular type of
  instrument in astronomy (60), with imagers a
  distant second (25)
• Most spectrometers also have an imaging mode, at
  least to support a target acquisition mode, so
  imaging systems are important
• Among the spectrometers built, not surprisingly
  the most popular type remains the simple long
  slit spectrometer
• An equal number of MOS and IFU based systems are
  either built or planned
• Given the large multiplex gain of these systems,
  MOS and IFU spectrometers tend to require the
  largest focal planes

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Current Market Share by Various Manufacturers

• Top histogram shows dominant manufacturers used
  in various instruments
• Effectively assumes 1 detector per instrument
• Others are in many cases are one-off devices in
  specialized instruments which together account
  for 20 of all instruments
• Bottom plot tallies all detectors sampled in
  survey so is a true head count of detectors in
  use

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Current Market Share by Various Manufacturers

• Regardless of how market share is assessed, E2V
  detectors are the most commonly used in
  ground-based astronomy
• Nearly half of all science detectors in
  instruments sampled are made by E2V
• Linked to previous plots demonstrating popularity
  of optical instruments in astronomy
• Large CCD mosaics that have been built no doubt
  enable E2V market share compared to NIR
  manufacturers, where comparably large mosaics
  have not been built

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Plate Scale and Field of View

• Most instruments use (surprisingly) small pixels,
  most at 0.1
• Lack of gt1 pixels is probably due to not
  sampling small telescopes which often have large
  fields
• Clearly a sweet spot in field size of
  instruments for fields in the 10-100 arcmin2
  range
• Extremely small fields are pretty much
  exclusively domain of AO
• Cant correct over large fields
• Extremely large fields on the right are mainly
  due to future ultra wide field instruments
  involving enormous CCD focal planes

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Plate Scale and Field of View

• Most instruments use (surprisingly) small pixels,
  most at 0.1
• Lack of gt1 pixels is probably due to not
  sampling small telescopes which often have large
  fields

• Clearly a sweet spot in field size of
  instruments for fields in the 10-100 arcmin2 range

• Extremely small fields are pretty much
  exclusively domain of AO
• Cant correct over large fields

• Extremely large fields on the right are mainly
  due to future ultra wide field instruments
  involving enormous CCD focal planes

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Typical Infrared Pixel Size Now and Tomorrow

• NIR instruments have pretty much locked into
  18-27 µm pixel format
• The the future, pixels of this size will remain
  popular
• Likewise MIR instruments have adopted pixels 2-3
  times bigger, consistent with larger point spread
  function at these longer wavelengths
• Shifting to considerably smaller pixels to reach
  larger array formats may pose problems for
  optical designs of infrared instruments
• Drives builders to faster optical systems and
  reduced tolerances which may be non-trivial to
  achieve in cryogenic instruments

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Typical CCD Pixel Size Now and Tomorrow

• Similarly, current and future optical instruments
  have pretty much standardized on 13-15 µm
  pixels
• 86 of current instruments use 13-15 µm pixels
• In all cases 15 um is the most often used, with
• 73 of future instruments sampled will use 13-15
  um pixels

CURRENT
FUTURE
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Typical Infrared Array Format, Now and Tomorrow

• 1024x1024 is the standard format used in NIR
  arrays today
• 2048x2048x devices likely have not been around
  long enough to become well established, with only
  15 of the market share
• In the future, the community clearly wants to
  switch to larger format device, with 75 of the
  future instruments sampled going with 2k NIR
  arrays
• Again, astronomers will take advantage of larger
  format IR detectors, when they become available

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Typical CCD Format, Now and Tomorrow
CURRENT

• 2x4k building block is, not surprisingly, by far
  the most popular current CCD format
• Future planned instruments will baseline 4x4k
  detectors as much as the more established 2x4k
  detectors
• 77 of future instruments expect to use either
  2x4k or 4x4k CCDs
• Clearly astronomers are eager to use ever larger
  CCDs

FUTURE
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Total Pixel Inventory, Now and Tomorrow
Optical Infrared

• Total of 1.9 Gpixels found in current
  instruments sampled by this survey
• Essentially all IR focal planes are lt10 Mpixel
• Most optical focal planes are also lt10 Mpixel,
  though some are much larger
• Have merged NIRMIR into Infrared

CURRENT
FUTURE
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Total Pixel Inventory, Now and Tomorrow

• The future looks similar in the infrared with
  most instruments having modest size focal planes
• The future at optical wavelengths include a lot
  more large focal planes
• The future market includes 7.7Gpixels of science
  grade detectors, gt90 of which is in the form of
  CCDs in the future More category (gt100 Mpixel
  focal planes)
• Note that lack of planned IR large format focal
  planes isnt due to lack of ambition on the part
  of IR astronomers - its due to lack of money

Optical Infrared
CURRENT
FUTURE
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Controller Types

• Includes all instruments (current and future) in
  survey
• SDSU clearly the most commonly used controller in
  astronomy, with 1 in 4 controllers being an SDSU
  system
• Huge range in controllers being used - total of
  44 different controllers identified in survey
• This is an area where we would all benefit from
  an industry standard
• Closest thing we have is SDSU

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Instrument Costs

• Most participants in the survey did not include a
  cost and, in general, it is difficult to make a
  detailed apples to apples comparisons due to
  various assumptions
• Does cost include labor, overhead, all parts,
  etc?
• Instead, have only assessed median costs of
  current and future instruments to look for basic
  trends

Median Instrument Cost Summary