History of Astronomical Instruments The early history: From the unaided eye to telescopes

The Human Eye Anatomy and Detection Characteristics

Anatomy of the Human Eye

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

Tycho Quadrant

Hevelius Sextant

Hevelius Quadrant

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 D 2, 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

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

William HerschelCaroline Herschel

Herschel 40 ft Telescope

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

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

Mirror Grinding Tool

Mirror Polishing Machine

Fine Ground Mirror

Mirror Polishing

Figuring the Asphere

Crossley 36” Reflector

Yerkes 40-inch Refractor

Drawing of the Moon (1865)

First Photograph of the Moon (1865)

The Limitations of Ground-based Observations Diffraction Seeing Sky Backgrounds

Diffraction

Wavefront Description of Optical System

Wavefronts of Two Well Separated Stars

When are Two Wavefront Distinguishable ?

Atmospheric Turbulence

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 VLT Observatory at Paranal, Chile

Modern Observatories The ESO-VLT Observatory at Paranal, Chile

Pu`u Poliahu UH 0.6-m UH 2.2-m The first telescopes on Mauna Kea ( )

Local Seeing Flow 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.

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

LOCAL TURBULENCE Mirror Seeing 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 The contribution to seeing due to turbulence over the mirror is given by:

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

Thermal Emission Analysis VLT Unit Telescope UT3 Enclosure 19 Feb h34 Local Time Wind summit: ENE, 4m/s Air Temp summit: 13.8C

Gemini South Dome

Coating - thermal properties

Enclosure coatings UKIRT- reflective bare aluminum UH- TiO 2 -based white paint GEMINI- Al-based Lo-Mit paint CFHT- TiO 2 -based white paint IRTF- reflective aluminum foil KECK- TiO 2 -based white paint SUBARU- - reflective Alclad siding

CFHT Keck IRTF Gemini Subaru UKIRT IfA

Coatings tested red metal primerACE CFHT white paintTriangle Paint Co. Gemini aluminum paintLo-Mit IRTF Al foil – 3.1mil3M product # 439 light blue acrylic latexACE color 24-D dark blue acrylic latexACE color 24-B

White Al foil Lo-Mit Primer

Solar spectrum

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

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

Sunset on Mauna Kea 5:42 p.m. 5:21 p.m. 4:34 p.m. 5:45 p.m. 5:49 p.m. 6:05 p.m. 6:24 p.m. 6:41 p.m. 6:46 p.m. Keck I and Subaru September 20, 1999

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

Night Sky Emission Lines at Optical Wavelengths

Sky Background in J, H, and K Bands

Sky Background in L and M Band

V-band sky brightness variations

J-band OH Emission Lines

H-band OH Emission Lines

K-band OH Emission Lines

Uncorrected

ADC Conceptual Design Linear ADC design Variable prism separation provides correction UV-to-near IR transmission requires fused silica optics Nulled Fully Open, Z=60 

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