teleskop modern as3200 lab. astronomi dasar ii prodi astronomi 2007/2008 b. dermawan
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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
Majewski
HST
LBT, abell.as.arizona.edu/~hill/mirror
Bely
Large Mirrors: Shapes, Materials & Types
Segmented mirrors
Majewski
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)
Bely
Large Mirrors: Shapes, Materials & Types
Segmented mirrors
Majewski
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
Majewski
Hobby-Eberly Telescope (HET)
South Africa Large Telescope (SALT)
Large Mirrors: Shapes, Materials & Types
Segmented mirrors
Majewski
Keck I & II
Large Mirrors: Shapes, Materials & Types
Segmented mirrors
Majewski
Large Binocular Telescope (LBT)
Large Mirrors: Shapes, Materials & Types
Tubes, Trusses, & Baffling
Majewski
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
Bely
Bely
Large Mirrors: Shapes, Materials & Types
Tubes, Trusses, & Baffling
Majewski
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
Bely
Demands for wide field imaging are more severe
Large Mirrors: Shapes, Materials & Types
Tubes, Trusses, & Baffling
Majewski
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)
Bely
Bely
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
Bely
Bely
Teleskop Subaru (1)
www.subarutelescope.org
Teleskop Subaru (2)
www.subarutelescope.org
Large Mirrors: Shapes, Materials & Types
The biggest existing telescopes
Majewski
IFA, Univ of Hawaii
Large Mirrors: Shapes, Materials & Types
The biggest existing telescopes
Majewski
Bely
Large Mirrors: Shapes, Materials & Types
Some Proposed/Planned Large, Ground-based Telescopes
Majewski
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
Majewski
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
Majewski
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
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