Teleskop Modern

AS3200 Lab. Astronomi Dasar IIProdi Astronomi 2007/2008B. Dermawan

To Dreamers, Then, Now, and Always

Majewski

Trends in Modern Telescope Development

• Light gathering power• Kualitas & sensitivitas inst

rumen efisiensi• Resolusi (kualitas citra & s

ensitivitas) efisiensi

Majewski

Bely

Trends in Modern Telescope Development

• Sensitivitas Instrumen- Perbaikan pada desain optik, optik, detektor- Temuan baru (fiber optics, holographic gratings)- Menemukan tempat observasi baru

• Resolusi- Guiding cepat & otomatis- Pemahaman yg lebih baik tentang efek seeing- Penentuan tempat observasi dgn seeing yg baik- Perbaikan pada cermin & desain dome- Active mirror figure & atmospheric compensation- Pengamatan space-based- Interferometry

Majewski

Bely

Large Mirrors: Shapes, Materials & Types

Telescope f-ratio

Majewski

• Fast primaries: biaya operasional, tabung kecil kukuh, kecil wind cross-section, secondary mirror lebih kecil

Bely

• Difficult decisions: tipe & konstruksi cermin utama, konfigurasi optik, struktur/ukuran/kontrol tel., desain instrumen optik, ukuran dome, tempat yg potensial utk teleskop, biaya total

Large Mirrors: Shapes, Materials & Types

Lightweighting mirror

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HST

LBT, abell.as.arizona.edu/~hill/mirror

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Large Mirrors: Shapes, Materials & Types

Segmented mirrors

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Size limited of monolithic mirrors: fasilitas pabrikan, sukar mendapatkan hasil homogen, sukar pada handling & transport, max. 4-m untuk space telescope

Advantages of segmented mirrors: massa rendah, singkat konstanta waktu termal, segmen dapat diganti, ukuran aperture tidak terbatas

Large Mirrors: Shapes, Materials & Types

Segmented mirrors

Majewski

However:all segments must be figured to be parts of one parent shape (“off-axis" paraboloidal segments tricky and expensive), all segments must be kept precisely and actively aligned despite changing gravity, thermal effects, wind, etc.

Segmentation geometry: “petals" / "keystone" -- radial/azimuthal segments, hexagons (put down in rings)

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Large Mirrors: Shapes, Materials & Types

Segmented mirrors

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1.8-m Guido Horn-d'Arturo

6-mirror (~4.5-m) to a single mirror 6.5-m MMT www.mmto.org/pr_images/upgrade.html

Large Mirrors: Shapes, Materials & Types

Segmented mirrors

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Hobby-Eberly Telescope (HET)

South Africa Large Telescope (SALT)

Large Mirrors: Shapes, Materials & Types

Segmented mirrors

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Keck I & II

Large Mirrors: Shapes, Materials & Types

Segmented mirrors

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Large Binocular Telescope (LBT)

Large Mirrors: Shapes, Materials & Types

Tubes, Trusses, & Baffling

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Heavy, under gravity de-collimate the optics, presents a large wind cross-section, prevents air from flowing across & cooling mirror

Serruir Truss: open structure based on isosceles triangles on a square base• When vertical triangles deflect, the parallelogram of horizontal triangles con

strains the tube ends to move in a parallel plane mass inefficiency & use of active optics

• Multi-bay structure

HST

KeckGemini

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Large Mirrors: Shapes, Materials & Types

Tubes, Trusses, & Baffling

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Preventing scattered light baffling• Generally conical or cylindrical tubes enclosing parts of the beam• Often include perpendicular vanes to force radiation to make

multiple scatters

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Demands for wide field imaging are more severe

Large Mirrors: Shapes, Materials & Types

Tubes, Trusses, & Baffling

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Reflections off of the primary or secondary: scattering of off-axis rays off of dust

Critically important for space telescope

HST: numerous vanes and both secondary and primary conical baffles (all black)

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Large Mirrors: Shapes, Materials & Types

Mounts

Majewski

Before 1980 nearly all telescopes were mounted with an equatorial mount: counteract Earth rotation by motion only on one, polar axis, simple correction with single speed, no field rotation in focal plane

Now most telescopes are built with altitude-azimuth (alt-az) mounts: neither axis changes direction with respect to gravity, structurally sturdier than equatorial, less massive, less expensive

BUT: three axes of rotation needed: altitude (h), azimuth (A), and field rotation, all three axes move with variable speed, could only do this with fast computers

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Teleskop Subaru (1)

www.subarutelescope.org

Teleskop Subaru (2)

www.subarutelescope.org

Large Mirrors: Shapes, Materials & Types

The biggest existing telescopes

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IFA, Univ of Hawaii

Large Mirrors: Shapes, Materials & Types

The biggest existing telescopes

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Bely

Large Mirrors: Shapes, Materials & Types

Some Proposed/Planned Large, Ground-based Telescopes

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Large Synoptic Survey Telescope (LSST) • Proposed 8.4-m telescope with enormous

10 square degree field• 3 billion pixel camera• Will cover the entire sky with 10 second

integrations every three nights• Find fast moving or variable objects• Build up a deep survey image of the sky

in multiple wavelengths

Large Mirrors: Shapes, Materials & Types

Some Proposed/Planned Large, Ground-based Telescopes

Majewski

Giant Magellan Telescope• Seven 8.4-m Arizona Mirror Lab

borosilicate honeycomb mirrors• Light gathering power equivalent to a

21.4-m filled aperture• Diffraction limited resolution equivalent

to a 24.5-m filled aperture• f/8.4 Gregorian with adaptive optics

secondary• Chile• Partners: Carnegie Observatories,

Harvard, MIT, SAO, Texas A&M, Arizona, Michigan, Texas

Large Mirrors: Shapes, Materials & Types

Some Proposed/Planned Large, Ground-based Telescopes

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Thirty Meter Telescope (TMT) project A joining of several separate efforts: California Extremely Large Telescope (CELT) -- Caltech/UC Giant Segmented Mirror Telescope (GSMT) -- AURA Very Large Optical Telescope (VLOT) -- Canada

Large Mirrors: Shapes, Materials & Types

Scientific productivity of telescopes

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Bely

Suggests that scientific productivity scales by collecting area

But cost is roughly proportional to diameter2 or diameter3, so the cost-effectiveness of a ground-based telescope is roughly independent of size, or maybe even somewhat favoring smaller apertures

Of course, there is some science that simply demands the largest telescopes

New Technology “Surfaces”Liquid mirror telescopes (LMTs)

Majewski

• Newton originally proposed using a rotating liquid (e.g., mercury) itself as a perfect paraboloid, but first done for 35 cm telescope in 1872

• Revived in last few decades (primarily by Canadian collaborations) as technical problems overcome

• Primary limitation is that they can only look at zenith: limits science to survey type projects, with drift-scan CCD imaging

http://www.phys.psu.edu/~cowen/popular-articles/sciam/1299musserbox6.html

New Technology “Surfaces”• Primary technical challenge is

suppression of ripples on surface from: wind, vibrations, misalignment of rotational axis

Air bearings are one modern solution to smooth, accurate rotation

• Primary practical problem is that mercury vapors and oxides are very toxic

• But a big advantage is cost: The Large Zenith Telescope, a 6-m LMT, is being built at a cost of about $500,000 (which is 1% the cost of a conventional telescope of similar aperture)

Majewski

http://www.phys.psu.edu/~cowen/popular-articles/sciam/1299musserbox6.html