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Teleskop Modern
AS3200 Lab. Astronomi Dasar II
Prodi Astronomi 2007/2008
B. Dermawan
Majewski
To Dreamers, Then, Now, and Always
Majewski
Trends in Modern Telescope Development
Bely
• Light gathering power
• Kualitas & sensitivitas
instrumen  efisiensi
• Resolusi (kualitas citra &
sensitivitas)  efisiensi
Majewski
Trends in Modern Telescope Development
• Sensitivitas Instrumen
Bely
- 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
Large Mirrors: Shapes, Materials & Types
Telescope f-ratio
• Difficult decisions: tipe & konstruksi cermin utama,
konfigurasi optik, struktur/ukuran/kontrol tel., desain
instrumen optik, ukuran dome, tempat yg potensial utk
teleskop, biaya total
Bely
• Fast primaries: biaya
operasional, tabung kecil 
kukuh, kecil wind crosssection, secondary mirror
lebih kecil
Majewski
Large Mirrors: Shapes, Materials & Types
Lightweighting mirror
LBT, abell.as.arizona.edu/~hill/mirror
HST
Bely
Majewski
Large Mirrors: Shapes, Materials & Types
Segmented mirrors
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
Majewski
Large Mirrors: Shapes, Materials & Types
Segmented mirrors
However:
all segments must be figured to be parts of one parent shape (“offaxis" 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
Majewski
Large Mirrors: Shapes, Materials & Types
Segmented mirrors
6-mirror (~4.5-m) to a single mirror 6.5-m MMT
www.mmto.org/pr_images/upgrade.html
1.8-m Guido Horn-d'Arturo
Majewski
Large Mirrors: Shapes, Materials & Types
Segmented mirrors
Hobby-Eberly Telescope (HET)
South Africa Large Telescope (SALT)
Majewski
Large Mirrors: Shapes, Materials & Types
Segmented mirrors
Keck I & II
Majewski
Large Mirrors: Shapes, Materials & Types
Segmented mirrors
Large Binocular Telescope (LBT)
Majewski
Large Mirrors: Shapes, Materials & Types
Tubes, Trusses, & Baffling
Heavy, under gravity  de-collimate the optics,
presents a large wind cross-section, prevents air
from flowing across & cooling mirror
Bely
Serruir Truss: open structure based on isosceles triangles on a square base
• When vertical triangles deflect, the parallelogram of horizontal triangles
constrains the tube ends to move in a parallel plane  mass inefficiency &
use of active optics
Gemini
Keck
• Multi-bay structure
Bely
HST
Majewski
Large Mirrors: Shapes, Materials & Types
Tubes, Trusses, & Baffling
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
Majewski
Large Mirrors: Shapes, Materials & Types
Tubes, Trusses, & Baffling
Bely
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
Majewski
Large Mirrors: Shapes, Materials & Types
Mounts
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 (altaz) 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
Majewski
Large Mirrors: Shapes, Materials & Types
The biggest existing telescopes
IFA, Univ of Hawaii
Majewski
Large Mirrors: Shapes, Materials & Types
The biggest existing telescopes
Bely
Majewski
Large Mirrors: Shapes, Materials & Types
Some Proposed/Planned Large, Ground-based Telescopes
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
Majewski
Large Mirrors: Shapes, Materials & Types
Some Proposed/Planned Large, Ground-based Telescopes
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
Majewski
Large Mirrors: Shapes, Materials & Types
Some Proposed/Planned Large, Ground-based Telescopes
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
Majewski
Large Mirrors: Shapes, Materials & Types
Scientific productivity of telescopes
Suggests that scientific productivity
scales by collecting area
But cost is roughly proportional to
diameter2 or diameter3, so the costeffectiveness 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
Bely
Majewski
New Technology “Surfaces”
Liquid mirror telescopes (LMTs)
• 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/populararticles/sciam/1299musserbox6.html
Majewski
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)
http://www.phys.psu.edu/~cowen/populararticles/sciam/1299musserbox6.html