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

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

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 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

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

H-band OH Emission Lines

Camera Construction Techniques 1. Pre-amplifier Pressure Vessel Vacuum pump port Liquid Nitrogen fill port Camera mounting Face-plate. 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. Mounting clamp

Camera Construction Techniques A cutaway diagram of the same camera is shown below. Thermally Electrical feed-through Vacuum Space Pressure vessel Pump Port Insulating Pillars Focal Plane of Telescope Telescope beam Optical window CCD CCD Mounting Block Thermal coupling Nitrogen can Activated charcoal ‘Getter’ Boil-off Face-plate

Camera Construction Techniques 5. CCD Temperature servo circuit board Platinum resistance thermometer Gold plated copper mounting block Top of LN2 can Pressure Vessel Signal wires to CCD Location points (x3) for insulating pillars that reference the CCD to the camera face-plate Aluminised Mylar sheet Retaining clamp The camera with the face-plate removed is shown below ‘Spider’. The CCD mounting block is stood off from the spider using insulating pillars.

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

Camera Construction Techniques 7. ‘Spider’ Vane CCD Clamp plate CCD Signal connector (x3) Copper rod or ‘cold finger’ used to cool the CCD. It is connected to an LN2 can. Gold plated copper CCD mounting block. CCD Package 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. FOS 1 Spectrograph