[X] My Assistant

[Mongo]

This topic came up on another thread (CoRoT Planets) and I thought that it deserved a thread of its own. Here is a list of ground-based optical telescopes with primary mirrors of at least 6.5 metres equivalent diameter. I include telescopes that are currently operational, under construction or in serious planning with significant funding support.

42m -- EELT (European Extremely Large Telescope) -- Planning -- ESO Council -- site to be selected by late 2009 -- based upon the Euro50 and OWL studies
30m -- TMT (Thirty Metre Telescope) -- Planning -- USA / Canada -- Mauna Kea, Hawaii, USA -- has received over 400 million dollars in donations and pledges to date
21.4m -- GMT (Giant Magellan Telescope) -- Construction -- USA / Australia -- Las Campanas, Chile -- primary mirror fabrication in progress
16.4m -- VLT (Very Large Telescope) -- Operational -- ESO Council - Cerra Paranal, Chile -- four monolithic-mirror 8.2-metre telescopes in combined interferometric mode
11.8m -- LBT (Large Binocular Telescope) -- Operational -- USA / Italy / Germany -- Mt. Graham, Arizona, USA -- two monolithic 8.4-metre primary mirrors
11.0m -- SALT (Southern African Large Telescope) -- Operational -- South Africa / USA / Germany / Poland / New Zealand / India -- Sutherland, South Africa -- segmented-mirror design
10.4m -- GTC (Gran Telescopio Canarias) -- Operational -- Spain / Mexico / USA -- La Palma, Canary Islands, Spain -- segmented-mirror design
10.0m -- Keck I -- Operational -- USA -- Mauna Kea, Hawaii, USA -- segmented-mirror design
10.0m -- Keck II -- Operational -- USA -- Mauna Kea, Hawaii, USA -- twin to Keck I
9.2m -- HET (Hobby-Eberly Telescope) -- Operational -- USA -- Mt. Foulkes, Texas, USA -- segmented-mirror design
8.4m -- LSST (Large Synoptic Survey Telescope) -- Planning -- USA -- Cerro Pachon, Chile -- this is the telescope that Google is helping to fund
8.3m -- Subaru -- Operational -- Japan -- Mauna Kea, Hawaii, USA -- monolithic mirror
8.1m -- Gemini North (Gillett) -- Operational -- USA / UK / Canada / Australia / Argentina / Brazil / Chile -- Mauna Kea, Hawaii, USA -- monolithic mirror
8.1m -- Gemini South -- Operational -- USA / UK / Canada / Australia / Argentina / Brazil / Chile -- Cerro Pachon, Chile -- twin to Gemini North
6.5m -- MMT -- Operational -- USA -- Mt. Hopkins, Arizona, USA -- converted from old MMT (Multiple Mirror Telescope) into a single monolithic mirror
6.5m -- Magellan I (Walter Baade) -- Operational -- USA -- La Serina, Chile -- monolithic mirror
6.5m -- Magellan II (Landan Clay) -- Operational -- USA -- La Serina, Chile -- twin of Magellan I

Bill

[Del Palmer]

Here's how the various best sites around the world compare in terms of seeing:

Median Seeing

0.07 Dome C in Antarctica (no telescopes yet)
0.45 Mauna Kea Observatory
0.55 Mt. Graham (Emerald Peak sites)
0.60 MMT (Mt. Hopkins/summit)
0.66 VLT (Paranal)
0.76 Magellan (Las Campanas) & ESO (La Silla)

It is quite remarkable how much the seeing varies, even at the same site. For example, at Mauna Kea, Subaru's average is 0.6 arcsec, versus 0.43 for CFHT.

The individual telescopes also produce "wakes" that interfere with other telescopes' seeing -- thus you don't want to populate the summit dome-to-dome.