William Keel <keel@bildad.astr.ua.edu>,
        Joseph Lazio <jlazio@patriot.net>,
	Steve Willner <swillner@cfa.harvard.edu>, Jennifer Imamura

The "largest" telescope is a bit difficult to determine.  One can
obtain many different answers, depending upon the adjectives placed in
front of "largest."  Nonetheless, what follows is one such list.  

A list of astronomical instruments is also at
<URL:http://www.futureframe.de/astro/instr/index.html>, and a list of
large optical telescopes is at
<URL:http://www.seds.org/billa/bigeyes.html>.

A list of space-based observatories is at
<URL:http://www.seds.org/~spider/oaos/oaos.html>.


(Optical/Infrared telescopes, nighttime)

The list below gives the largest optical telescopes operating today.
For complicated pupil shapes, the effective aperture diameter is
given.  Location is geographic; we omit most organizational details,
amusing and intricate as they may be.  The list has been truncated at
3 m because there are so many telescopes of that size or smaller.
URL's are given where known.

Aperture  Name              Location 
10.0      Keck I            Mauna Kea, Hawaii
   (mirror composed of 36 segments)
   <URL:http://astro.caltech.edu/mirror/keck/index.html>
 6.5      Multiple Mirror   Mt. Hopkins, Arizona
   (6 mirrors, 1.8 m each; see also B.03)
   <URL:http://sculptor.as.arizona.edu/foltz/www/mmt.html>
 6.0      BTA               Nizhny Arkhyz, Russia
   (Bolshoi Teleskop Azimutalnyi = Large Altazimuth Telescope)
   <URL:http://www.sao.ru/>
 5.0      Hale              Palomar Mountain, California
   <URL:http://astro.caltech.edu/observatories/palomar/public/index.html>
 4.2  William Herschel      La Palma, Canary Islands
   <URL:http://ing.iac.es/WHT.html>
 4.0  Victor Blanco	    Cerro Tololo, Chile
   <URL:http://www.ctio.noao.edu/4m/base4m.html>
 4.0  Mayall                Kitt Peak, Arizona
   <URL:http://www.noao.edu/kpno/kpno.html>
 3.9  Anglo-Australian      Siding Spring, Australia
   <URL:http://www.aao.gov.au/>
 3.8  UK Infrared           Mauna Kea, Hawaii
   <URL:http://www.jach.hawaii.edu/UKIRT/>
 3.6  ESO                   Cerro La Silla, Chile
   <URL:http://www.ls.eso.org/>
 3.6  Canada-France-Hawaii  Mauna Kea, Hawaii
   <URL:http://www.cfht.hawaii.edu/>
 3.5  New Technology        Cerro La Silla, Chile
   <URL:http://www.eso.org/NTT/>
 3.5  MPI-CAHA              Calar Alto, Spain
   <URL:http://www.mpia-hd.mpg.de/CAHA/>
 3.5  ARC                   Apache Point, New Mexico (mostly remote control)
   <URL:http://www.apo.nmsu.edu/>
 3.5  WIYN                  Kitt Peak, Arizona
   <URL:http://www.noao.edu/wiyn/>
 3.5  Starfire		    Kirtland AFB, New Mexico
   <URL:http://www.sor.plk.af.mil/default.html>
 3.0  Shane                 Mount Hamilton, California
   <URL:
   http://cgi.irving.org/cgi-bin/irving-cgi-bin/xplore.pl?lick+shnentry+A+M
   >
 3.0  NASA IRTF             Mauna Kea, Hawaii
   <URL:http://irtf.ifa.hawaii.edu/>

Other telescopes of note:

Solar Telescope:

Global Oscillation Network Group (GONG), six sites around the world
  for velocity imaging
  http://helios.tuc.noao.edu/gonghome.html 

Largest single dish radio telescope: Arecibo Observatory
  (Nat. Astron. & Ionosphere Center, Cornell U.)  305-m, Puerto Rico
  <URL:http://www.naic.edu/>

Largest fully-steerable single dish radio telescope: Max Planck
  Institut fuer Radioastronomie, 100 m, Effelsburg, Germany
  <URL:http://www.mpifr-bonn.mpg.de/effberg.html>

Largest millimeter wave radio telescope: Nobeyama Radio Observatory,
  45m, Japan
  <URL:http://radio.utsunomiya-u.ac.jp/NAO/nobeyama.html>

Largest sub-millimeter radio telescope: James Clerk Maxwell Telescope
  (Joint Astron. Center = UK, Canada, Netherlands), Mauna Kea, 15 m
  <URL:http://www.jach.hawaii.edu/JCMT/>

Largest (connected-element) radio interferometric arrays: 
  Very Large Array (NRAO, New Mexico), 
  27 dishes, each 26.4 m effective diameter
  The maximum separation between antennas is ~35 km.
  <URL:http://www.aoc.nrao.edu/vla/html/VLAhome.shtml>

  MERLIN (NRAL, University of Manchester, UK)
  up to 8 dishes, various specifications. 
  The maximum separation between antennae is 217 km (between the
  Cambridge and Knockin dishes). 
  <URL:http://www.jb.man.ac.uk/merlin/>
  [MERLIN actually uses radio links between the antenna elements, so
  maybe it should go into a separate category.]

Longest-baseline (dedicated) radio interferometric array: Very Long
  Baseline Array (NRAO), 10 dishes, each 26.4 m effective diameter,
  United States. The maximum separation between antennas is ~8600 km,
  between the islands of St. Croix and Hawaii.
  <URL:http://www.aoc.nrao.edu/vlba/html/VLBA.html>

HALCA (ISAS), 8 m dish, in Earth orbit
  <URL:http://www.vsop.isas.ac.jp/>

Infrared:
Infrared Space Observatory (ISO) (ESA)
  <URL:http://isowww.estec.esa.nl/>

Ultraviolet:

Extreme Ultraviolet Explorer (EUVE) (NASA)
   <URL:http://www.cea.berkeley.edu/>

International Ultraviolet Explorer (IUE) [defunct] (NASA, PPARC and ESA)
   <URL:http://www.vilspa.esa.es/iue/iue.html>

X-ray:

Chandra, the Advanced X-ray Astrophysics Facility (NASA)
   <URL:http://asc.harvard.edu/>

X-Ray Astronomy Satellite (SAX) (ESA)
   <URL:http://www.sdc.asi.it/>

X-Ray Timing Explorer (XTE) (NASA), 2 instruments: PCA & HEXTE
   <URL:http://heasarc.gsfc.nasa.gov/docs/xte/XTE.html>

ASCA/ASTRO-D (ISAS)
   <URL:http://www.astro.isas.ac.jp/xray/mission/asca/ascaE.html>

Roentgen Satellite (ROSAT) (MPE)
   <URL:http://wave.xray.mpe.mpg.de/rosat/>

Einstein, the second High Energy Astronomy Observatory (HEAO-B) [defunct]
   (NASA), 5 instruments: IPC, HRI, SSS, FPCS, & OGS
   <URL:http://heasarc.gsfc.nasa.gov/docs/einstein.html>

Gamma-ray:

Fred Lawrence Whipple Gamma-Ray Observatory (SAO), a 10 m and 11 m
   instrument
   <URL:http://linmax.sao.arizona.edu/help/FLWO/whipple.html>

CANGAROO (U. Adelaide & Nippon), 4 4-m cameras
   <URL:http://www.physics.adelaide.edu.au/astrophysics/cangaroo.html>

Compton Gamma-Ray Observatory (NASA) [space-based], 
   4 instruments: OSSE, EGRET, COMPTEL, & BATSE
   <URL:http://cossc.gsfc.nasa.gov/cossc/cgro.html>

Cosmic ray:

The High Resolution Fly's Eye Cosmic Ray Detector HiRes 
   <URL:http://www.physics.adelaide.edu.au/astrophysics/FlysEye.html>