Sky and Telescope - November 2018 - 4

SPECTRUM

by Peter Tyson

Supersize Me

The Essential Guide to Astronomy

PROFESSIONAL ASTRONOMERS, just like amateurs, suffer from that

widespread afﬂiction known as aperture creep. If only we had a scope
twice that size, they fantasize, think what we'd discover.
Chile's Las Campanas Observatory already hosts the twin
Magellan Telescopes, each bearing a 6.5-meter (21-foot) mirror. But
soon it will boast the Giant Magellan Telescope. This behemoth will combine
seven 8.4-meter mirrors for an effective aperture of 24.5 meters (80 feet). The
two 10-meter Keck telescopes atop Mauna Kea in Hawai'i do phenomenal science. Yet astronomers hope eventually to add another telescope just steps away
with a mirror effectively 30 meters in diameter.
European pros might have the most pronounced aperture creep of all. The
four unit telescopes (8.2 m each) that make up the European Southern Observatory's Very Large Telescope have conducted groundbreaking astronomy for
more than a decade. But the ESO is now building the Extremely Large Telescope
(39.3 m). If European astronomers had had their way, the ESO instead would be
erecting the Overwhelmingly Large Telescope (100 m).
I'm not making these names up. One wonders what they'd dub the next
iteration: The Astronomically Large Telescope? The Unimaginably Large Telescope? Suitable adverbs would run out long before their lofty notions.
This ever-bigger tendency is not limited to single-object observing. Large survey projects like the Sloan Digital Sky Survey (2.5 m) will pale, at least in terms
of total data collected, beside next-gen survey instruments like the Large Synoptic Survey Telescope (8.4 m). The SDSS total data volume is about 40 terabytes;
LSST will gather 15 terabytes of raw data every night (S&T: Sept. 2016, p. 16).
Nor does "bigger is better" conﬁne itself to optical and near-infrared
astronomy. The Arecibo Observatory (305 m), for instance, recently ceded
the distinction of world's largest single-dish radio telescope to China's Fivehundred-meter Aperture Spherical Radio Telescope, or FAST (500 m). Even space
telescopes creep. The James Webb Space Telescope (6.5 m) will explore far more
deeply than is possible with either the Spitzer Space Telescope (0.85 m) - which
focuses on the infrared as JWST will - or the Hubble Space Telescope (2.4 m).
Creep is a good thing for astronomy, of course. Those three monster optical
telescopes alone - the Giant Magellan, the Thirty Meter, and the Extremely
Large - will revolutionize our understanding of the universe. So huge are they
in signiﬁcance that we're devoting two articles to them. The ﬁrst, on page 14,
describes the telescopes in general; the second, in next month's issue, goes into
their instrumentation and the key science questions they'll help us address.
Amateurs: Isn't it reassuring to know you're not alone
in your predicament?

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Sky and Telescope - November 2018

Table of Contents for the Digital Edition of Sky and Telescope - November 2018