Sky and Telescope - November 2018 - 19
of our many activities," he says. In 2024, the Giant Magellan
Telescope may start science operations as a half-grown giant,
with a primary made up of only a few "eyes" instead of the
full seven. That would hardly compromise the angular resolution of the observations, but it would of course reduce the
sensitivity of the instrument: With four mirrors, for example,
the GMT would have the same light-gathering power as an
imaginary 17-m telescope. However, barring unexpected setbacks, McCarthy remains confident: "No way the GMT will
end as a four-mirror telescope."
G M TO CORPOR ATION (3); T M T: T M T IN TER N ATION A L OBSERVATORY
Thinking Big
For the Carnegie Institution for Science, a founding partner in the GMT project, it made a lot of sense to construct
the new telescope close to where they already are operating
the two original Magellan Telescopes. After all, GMT could
be described as Magellan on steroids. Likewise, the Thirty
Meter Telescope (TMT) is a pumped-up version of Keck, and
it should come as no surprise that the California Institute of
Technology (Caltech) and the University of California want
to build their new monster telescope at Mauna Kea, Hawai'i
- close to their original 10-m Keck twins.
The Thirty Meter Telescope is going to be huge. While
the primary mirrors of the two Keck Telescopes consist of
just 36 hexagonal segments (a design pioneered by the late
astronomer Jerry Nelson), TMT will have no fewer than 492
segments. Together, they constitute a 30-m wide hyperboloidal mirror. Measuring 1.44 m across, each segment is stiff
enough to resist deformations due to gravity, wind load, or
temperature changes. Still, active support systems are needed
to keep the segments precisely positioned with respect to one
another under all circumstances.
Because of the overall shape of the TMT mirror, the segments come in 82 different types (six of each), their asymmetric curvature depending on the distance from the center.
They are produced using a technique known as stressed mirror
polishing. Carefully calculated external stresses are applied to
each mirror blank, so that it can be polished into a spherical
shape, which is much easier than changing the techniques
to match 82 different shapes. Upon release of the external
forces, the mirror springs back to the desired off-axis, asymmetric shape. Every work day, two of the 492 segments will
be recoated in a giant coating plant next to the telescope,
switched out of the primary with spares every two weeks.
After about a year, each and every segment will have received
a new reflective layer (probably silver).
The TMT's 3.1-m convex secondary mirror is also a hyperboloid. The secondary is 20% larger than the primary mirror of the Hooker Telescope, which was the world's largest
reflector until just 70 years ago. Even the flat tertiary mirror
is larger, with a 3.5-by-2.5-m elliptical shape. Thanks to its
optical design, the TMT has a surprisingly large field of view of
almost 20 arcminutes, two-thirds of the apparent diameter of
the full Moon. Another impressive feature of the telescope is
its elegant, spherical enclosure, which will reach as high as an
18-story building. Known as a calotte dome, it has a tilted moving structure and a large circular opening.
At almost 700 square meters, the light-collecting area of
the TMT will be some 80% larger than that of the GMT. Of
course, the Thirty Meter Telescope will also be outfitted with
adaptive optics, using multiple lasers. Unfortunately, just as
with the GMT, the necessary funds - estimated at some $1.4
billion - are not yet fully secured, says TMT International
Observatory (TIO) board member Thomas Soifer (Caltech),
despite a generous $200 million grant from the Gordon and
Betty Moore Foundation. "We really need a major new partner, like the National Science Foundation," he says. A descope
plan is available, if necessary.
Pacific Protest
There have been many issues regarding the TMT's location.
A planned groundbreaking ceremony on October 7, 2014,
was disrupted by Native Hawaiians who protested against
yet another large telescope on the summit of their sacred
mountain. "It was a surprise," recalls TIO's executive director Edward Stone (Caltech). "We had spent eight years on
environmental impact studies and listening to the community." In late 2015, the Hawaiian Supreme Court vacated
the original building permit on procedural grounds. After
many public hearings, the state's Board of Land and Natural
Resources granted a fresh construction permit in September
2017, but opponents filed a notice of appeal with the state
Supreme Court. "You'll be amazed by all the things lawyers
can do," says Soifer.
Meanwhile, the TIO board started to develop Plan B, just
in case. Instead of building the TMT at Mauna Kea, the new
instrument could find a home at the Roque de los Muchachos Observatory, on the Spanish island of La Palma, off the
coast of Morocco in the Atlantic Ocean. La Palma already
hosts the 10.4-m Gran Telescopio Canarias - a near-identi-
THIRTY METER
TELESCOPE
sk yandtelescope.com * N OV E M B E R 2 018
19
http://www.skyandtelescope.com
Sky and Telescope - November 2018
Table of Contents for the Digital Edition of Sky and Telescope - November 2018
Contents
Sky and Telescope - November 2018 - Cover1
Sky and Telescope - November 2018 - Cover2
Sky and Telescope - November 2018 - 1
Sky and Telescope - November 2018 - Contents
Sky and Telescope - November 2018 - 3
Sky and Telescope - November 2018 - 4
Sky and Telescope - November 2018 - 5
Sky and Telescope - November 2018 - 6
Sky and Telescope - November 2018 - 7
Sky and Telescope - November 2018 - 8
Sky and Telescope - November 2018 - 9
Sky and Telescope - November 2018 - 10
Sky and Telescope - November 2018 - 11
Sky and Telescope - November 2018 - 12
Sky and Telescope - November 2018 - 13
Sky and Telescope - November 2018 - 14
Sky and Telescope - November 2018 - 15
Sky and Telescope - November 2018 - 16
Sky and Telescope - November 2018 - 17
Sky and Telescope - November 2018 - 18
Sky and Telescope - November 2018 - 19
Sky and Telescope - November 2018 - 20
Sky and Telescope - November 2018 - 21
Sky and Telescope - November 2018 - 22
Sky and Telescope - November 2018 - 23
Sky and Telescope - November 2018 - 24
Sky and Telescope - November 2018 - 25
Sky and Telescope - November 2018 - 26
Sky and Telescope - November 2018 - 27
Sky and Telescope - November 2018 - 28
Sky and Telescope - November 2018 - 29
Sky and Telescope - November 2018 - 30
Sky and Telescope - November 2018 - 31
Sky and Telescope - November 2018 - 32
Sky and Telescope - November 2018 - 33
Sky and Telescope - November 2018 - 34
Sky and Telescope - November 2018 - 35
Sky and Telescope - November 2018 - 36
Sky and Telescope - November 2018 - 37
Sky and Telescope - November 2018 - 38
Sky and Telescope - November 2018 - 39
Sky and Telescope - November 2018 - 40
Sky and Telescope - November 2018 - 41
Sky and Telescope - November 2018 - 42
Sky and Telescope - November 2018 - 43
Sky and Telescope - November 2018 - 44
Sky and Telescope - November 2018 - 45
Sky and Telescope - November 2018 - 46
Sky and Telescope - November 2018 - 47
Sky and Telescope - November 2018 - 48
Sky and Telescope - November 2018 - 49
Sky and Telescope - November 2018 - 50
Sky and Telescope - November 2018 - 51
Sky and Telescope - November 2018 - 52
Sky and Telescope - November 2018 - 53
Sky and Telescope - November 2018 - 54
Sky and Telescope - November 2018 - 55
Sky and Telescope - November 2018 - 56
Sky and Telescope - November 2018 - 57
Sky and Telescope - November 2018 - 58
Sky and Telescope - November 2018 - 59
Sky and Telescope - November 2018 - 60
Sky and Telescope - November 2018 - 61
Sky and Telescope - November 2018 - 62
Sky and Telescope - November 2018 - 63
Sky and Telescope - November 2018 - 64
Sky and Telescope - November 2018 - 65
Sky and Telescope - November 2018 - 66
Sky and Telescope - November 2018 - 67
Sky and Telescope - November 2018 - 68
Sky and Telescope - November 2018 - 69
Sky and Telescope - November 2018 - 70
Sky and Telescope - November 2018 - 71
Sky and Telescope - November 2018 - 72
Sky and Telescope - November 2018 - 73
Sky and Telescope - November 2018 - 74
Sky and Telescope - November 2018 - 75
Sky and Telescope - November 2018 - 76
Sky and Telescope - November 2018 - 77
Sky and Telescope - November 2018 - 78
Sky and Telescope - November 2018 - 79
Sky and Telescope - November 2018 - 80
Sky and Telescope - November 2018 - 81
Sky and Telescope - November 2018 - 82
Sky and Telescope - November 2018 - 83
Sky and Telescope - November 2018 - 84
Sky and Telescope - November 2018 - Cover3
Sky and Telescope - November 2018 - Cover4
https://www.nxtbook.com/nxtbooks/aas/st_202412
https://www.nxtbook.com/nxtbooks/aas/st_202411
https://www.nxtbook.com/nxtbooks/aas/st_202410
https://www.nxtbook.com/nxtbooks/aas/st_202409
https://www.nxtbook.com/nxtbooks/aas/st_202408
https://www.nxtbook.com/nxtbooks/aas/st_202407
https://www.nxtbook.com/nxtbooks/aas/st_202406
https://www.nxtbook.com/nxtbooks/aas/st_202405
https://www.nxtbook.com/nxtbooks/aas/st_202404_qr
https://www.nxtbook.com/nxtbooks/aas/st_202404
https://www.nxtbook.com/nxtbooks/aas/st_202403
https://www.nxtbook.com/nxtbooks/aas/st_202402
https://www.nxtbook.com/nxtbooks/aas/st_202401_aus
https://www.nxtbook.com/nxtbooks/aas/st_202401
https://www.nxtbook.com/nxtbooks/aas/st_202312_aus
https://www.nxtbook.com/nxtbooks/aas/st_202312
https://www.nxtbook.com/nxtbooks/aas/st_202311
https://www.nxtbook.com/nxtbooks/aas/st_202310
https://www.nxtbook.com/nxtbooks/aas/st_202309
https://www.nxtbook.com/nxtbooks/aas/st_202308
https://www.nxtbook.com/nxtbooks/aas/st_202307
https://www.nxtbook.com/nxtbooks/aas/st_202306
https://www.nxtbook.com/nxtbooks/aas/st_202305
https://www.nxtbook.com/nxtbooks/aas/st_202304
https://www.nxtbook.com/nxtbooks/aas/st_202304_qr
https://www.nxtbook.com/nxtbooks/aas/st_202303
https://www.nxtbook.com/nxtbooks/aas/st_202302
https://www.nxtbook.com/nxtbooks/aas/st_202301
https://www.nxtbook.com/nxtbooks/aas/st_202212
https://www.nxtbook.com/nxtbooks/aas/st_202211
https://www.nxtbook.com/nxtbooks/aas/st_202210
https://www.nxtbook.com/nxtbooks/aas/st_202209
https://www.nxtbook.com/nxtbooks/aas/st_202208
https://www.nxtbook.com/nxtbooks/aas/st_202207
https://www.nxtbook.com/nxtbooks/aas/st_202206
https://www.nxtbook.com/nxtbooks/aas/st_202205
https://www.nxtbook.com/nxtbooks/aas/st_202204
https://www.nxtbook.com/nxtbooks/aas/st_202203
https://www.nxtbook.com/nxtbooks/aas/st_202202
https://www.nxtbook.com/nxtbooks/aas/st_202201
https://www.nxtbook.com/nxtbooks/aas/st_202112
https://www.nxtbook.com/nxtbooks/aas/st_202111
https://www.nxtbook.com/nxtbooks/aas/st_202110
https://www.nxtbook.com/nxtbooks/aas/st_202109
https://www.nxtbook.com/nxtbooks/aas/st_202108
https://www.nxtbook.com/nxtbooks/aas/st_202107
https://www.nxtbook.com/nxtbooks/aas/st_202106
https://www.nxtbook.com/nxtbooks/aas/st_202105
https://www.nxtbook.com/nxtbooks/aas/st_202104
https://www.nxtbook.com/nxtbooks/aas/st_202103
https://www.nxtbook.com/nxtbooks/aas/st_202102
https://www.nxtbook.com/nxtbooks/aas/st_202101
https://www.nxtbook.com/nxtbooks/aas/skywatch_2021
https://www.nxtbook.com/nxtbooks/aas/st_202012
https://www.nxtbook.com/nxtbooks/aas/st_202011
https://www.nxtbook.com/nxtbooks/aas/st_202010
https://www.nxtbook.com/nxtbooks/aas/st_202009
https://www.nxtbook.com/nxtbooks/aas/st_202008
https://www.nxtbook.com/nxtbooks/aas/st_202007
https://www.nxtbook.com/nxtbooks/aas/st_202006
https://www.nxtbook.com/nxtbooks/aas/st_202005
https://www.nxtbook.com/nxtbooks/aas/st_202004
https://www.nxtbook.com/nxtbooks/aas/st_202003
https://www.nxtbook.com/nxtbooks/aas/st_202002
https://www.nxtbook.com/nxtbooks/aas/st_202001
https://www.nxtbook.com/nxtbooks/aas/st_201912
https://www.nxtbook.com/nxtbooks/aas/st_201911
https://www.nxtbook.com/nxtbooks/aas/st_201910
https://www.nxtbook.com/nxtbooks/aas/st_201909
https://www.nxtbook.com/nxtbooks/aas/st_201908
https://www.nxtbook.com/nxtbooks/aas/st_201907
https://www.nxtbook.com/nxtbooks/aas/st_201906
https://www.nxtbook.com/nxtbooks/aas/st_201905
https://www.nxtbook.com/nxtbooks/aas/st_201904
https://www.nxtbook.com/nxtbooks/aas/st_201903
https://www.nxtbook.com/nxtbooks/aas/st_201902
https://www.nxtbook.com/nxtbooks/aas/st_201901
https://www.nxtbook.com/nxtbooks/aas/st_201812
https://www.nxtbook.com/nxtbooks/aas/st_201811
https://www.nxtbook.com/nxtbooks/aas/st_201810
https://www.nxtbook.com/nxtbooks/aas/st_201809
https://www.nxtbook.com/nxtbooks/aas/st_201808
https://www.nxtbook.com/nxtbooks/aas/st_201807
https://www.nxtbook.com/nxtbooks/aas/st_201806
https://www.nxtbook.com/nxtbooks/aas/st_201805
https://www.nxtbook.com/nxtbooks/aas/st_201804
https://www.nxtbook.com/nxtbooks/aas/st_201803
https://www.nxtbook.com/nxtbooks/aas/st_201802
https://www.nxtbook.com/nxtbooks/aas/st_201801
https://www.nxtbook.com/nxtbooks/aas/st_201712
https://www.nxtbook.com/nxtbooks/aas/st_201711
https://www.nxtbook.com/nxtbooks/aas/st_201710
https://www.nxtbook.com/nxtbooks/aas/st_201709
https://www.nxtbook.com/nxtbooks/aas/st_201708
https://www.nxtbook.com/nxtbooks/aas/st_201707
https://www.nxtbook.com/nxtbooks/aas/st_201706
https://www.nxtbook.com/nxtbooks/aas/st_201705
https://www.nxtbook.com/nxtbooks/aas/st_201704
https://www.nxtbook.com/nxtbooks/aas/st_201703
https://www.nxtbook.com/nxtbooks/aas/st_201702
https://www.nxtbook.com/nxtbooks/aas/st_201701
https://www.nxtbook.com/nxtbooks/aas/st_201612
https://www.nxtbook.com/nxtbooks/aas/st_201611
https://www.nxtbook.com/nxtbooks/aas/st_201610
https://www.nxtbook.com/nxtbooks/aas/st_201609
https://www.nxtbook.com/nxtbooks/aas/st_201608
https://www.nxtbook.com/nxtbooks/aas/st_201607
https://www.nxtbook.com/nxtbooks/aas/st_201606
https://www.nxtbook.com/nxtbooks/aas/st_201605
https://www.nxtbook.com/nxtbooks/aas/st_201604
https://www.nxtbook.com/nxtbooks/aas/st_201603
https://www.nxtbook.com/nxtbooks/aas/st_201602
https://www.nxtbook.com/nxtbooks/aas/st_201601
https://www.nxtbook.com/nxtbooks/aas/st_201512
https://www.nxtbook.com/nxtbooks/aas/st_201511
https://www.nxtbook.com/nxtbooks/aas/st_201510
https://www.nxtbook.com/nxtbooks/aas/st_201509
https://www.nxtbook.com/nxtbooks/aas/st_201508
https://www.nxtbook.com/nxtbooks/aas/st_201507
https://www.nxtbook.com/nxtbooks/aas/st_201506
https://www.nxtbook.com/nxtbooks/aas/st_201505
https://www.nxtbook.com/nxtbooks/aas/st_201504
https://www.nxtbook.com/nxtbooks/aas/st_201503
https://www.nxtbook.com/nxtbooks/aas/st_201502
https://www.nxtbook.com/nxtbooks/aas/st_201501
https://www.nxtbook.com/nxtbooks/aas/st_201412
https://www.nxtbook.com/nxtbooks/aas/st_201411
https://www.nxtbook.com/nxtbooks/aas/st_201410
https://www.nxtbook.com/nxtbooks/aas/st_201409
https://www.nxtbook.com/nxtbooks/aas/st_201408
https://www.nxtbook.com/nxtbooks/aas/st_201407
https://www.nxtbook.com/nxtbooks/aas/st_201406
https://www.nxtbook.com/nxtbooks/aas/st_mars
https://www.nxtbook.com/nxtbooks/aas/st_201405
https://www.nxtbook.com/nxtbooks/aas/st_201404
https://www.nxtbook.com/nxtbooks/aas/st_201403
https://www.nxtbook.com/nxtbooks/aas/st_201402
https://www.nxtbook.com/nxtbooks/aas/st_201401
https://www.nxtbook.com/nxtbooks/aas/st_201312
https://www.nxtbook.com/nxtbooks/aas/st_201311
https://www.nxtbook.com/nxtbooks/aas/st_201310
https://www.nxtbook.com/nxtbooks/aas/st_201309
https://www.nxtbook.com/nxtbooks/aas/st_201308
https://www.nxtbook.com/nxtbooks/aas/st_201307
https://www.nxtbook.com/nxtbooks/aas/st_201306
https://www.nxtbook.com/nxtbooks/aas/st_201305
https://www.nxtbook.com/nxtbooks/aas/st_201304
https://www.nxtbook.com/nxtbooks/aas/st_201303
https://www.nxtbook.com/nxtbooks/aas/st_201302
https://www.nxtbook.com/nxtbooks/aas/st_201301
https://www.nxtbook.com/nxtbooks/aas/st_201212
https://www.nxtbook.com/nxtbooks/aas/st_201211
https://www.nxtbook.com/nxtbooks/aas/st_201210
https://www.nxtbook.com/nxtbooks/aas/st_201209
https://www.nxtbook.com/nxtbooks/aas/st_201208
https://www.nxtbook.com/nxtbooks/aas/st_201207
https://www.nxtbook.com/nxtbooks/aas/st_201206
https://www.nxtbook.com/nxtbooks/aas/st_201205
https://www.nxtbook.com/nxtbooks/aas/st_201204
https://www.nxtbook.com/nxtbooks/aas/st_201203
https://www.nxtbook.com/nxtbooks/aas/st_201202
https://www.nxtbook.com/nxtbooks/aas/st_201201
https://www.nxtbook.com/nxtbooks/aas/st_201112
https://www.nxtbook.com/nxtbooks/aas/st_201111
https://www.nxtbook.com/nxtbooks/aas/st_201110
https://www.nxtbook.com/nxtbooks/aas/st_201109
https://www.nxtbook.com/nxtbooks/aas/st_201108
https://www.nxtbook.com/nxtbooks/aas/st_201107
https://www.nxtbook.com/nxtbooks/aas/st_201106
https://www.nxtbook.com/nxtbooks/aas/st_201105
https://www.nxtbook.com/nxtbooks/aas/st_201104
https://www.nxtbook.com/nxtbooks/aas/st_201103
https://www.nxtbook.com/nxtbooks/aas/st_201102
https://www.nxtbook.com/nxtbooks/aas/st_201101
https://www.nxtbook.com/nxtbooks/aas/st_201012
https://www.nxtbook.com/nxtbooks/aas/st_201011
https://www.nxtbook.com/nxtbooks/aas/st_201010
https://www.nxtbook.com/nxtbooks/aas/st_201009
https://www.nxtbook.com/nxtbooks/aas/st_201008
https://www.nxtbook.com/nxtbooks/aas/st_201007
https://www.nxtbook.com/nxtbooks/aas/st_201006
https://www.nxtbook.com/nxtbooks/aas/st_201005
https://www.nxtbook.com/nxtbooks/aas/st_201004
https://www.nxtbook.com/nxtbooks/aas/st_201003
https://www.nxtbook.com/nxtbooks/aas/st_201002
https://www.nxtbook.com/nxtbooks/aas/st_201001
https://www.nxtbookmedia.com