Sky and Telescope - June 2017 - 31

p HERA One of four SKA precursor projects, HERA detects radio signals from neutral hydrogen, studying the large-scale cosmic structure that
existed before and during the Epoch of Reionization.

to make the universe shine. Similar observations will be carried out in South Africa's Great Karoo by the HERA telescope
(Hydrogen Epoch of Reionization Array), which is the fourth
and ﬁnal SKA precursor instrument. Next year, HERA will
consist of some 350 simple stationary wire-mesh dishes, each
14 meters across and sitting shoulder-to-shoulder to catch
low-frequency radio waves from the zenith.
By the end of this year, the detailed design and the construction proposal for the ﬁrst phase of the Square Kilometre
Array will be completed. Diamond expects construction to

SK A SOU TH A FRICA

WHAT SQUARE KILOMETER?
The Square Kilometre Array (British spelling) is named
after the planned total collecting area of its second
phase (SKA2). However, the ﬁrst phase of the project
(SKA1) will be much smaller. SKA1-mid, consisting of a
couple hundred dishes in South Africa, will end up with
a total collecting area of some 33,000 m2 (0.033 km2);
SKA1-low, in Australia, will have a collecting area of 0.4
km2, basically due to the large concentration of antenna
ﬁelds in the core region of the array (so the collecting
area won't grow by a factor of ten when SKA2 is
realized). Combined, SKA1 will have a collecting area
of less than half a square kilometer. For comparison:
the recently completed Chinese Five-hundred-meter
Aperture Spherical Radio Telescope (FAST; S&T: Feb.
2017, p. 26), the largest single-dish instrument in the
world, has a collecting area of 0.2 km2.

start next year. In fact, the ﬁrst 12-meter antenna has already
arrived on site in South Africa.
"We'll have early science results in 2021, and SKA1 will
be fully operational in 2024," Diamond says. "It's a huge
challenge. We're developing and constructing something no
one has ever built before." Asked about the prospects for the
second phase of the project, the SKA director admits that
none of the 12 member countries has committed themselves
to building SKA2 yet. "There's always the risk of cancellation,
but it doesn't particularly keep me awake at night," he says.
Nor me. What does keep me awake, both in the South
African Karoo and in the Australian outback, is the unbelievable view of the star-studded night sky - a universe ﬁlled
with wonder. Ten years from now, many outstanding cosmic
mysteries may have been solved by the sheer power of humankind's largest and most sensitive astronomical observatory
ever. And there's little doubt that the Square Kilometre Array
- even if only phase 1 will ever be realized - is going to present us with a lot of scientiﬁc surprises, too. Says Diamond:
"When the Hooker telescope on Mount Wilson started operations in 1917, no one expected the discovery of the expansion
of the universe. I have really no idea what the SKA will be
famous for a century from now."
¢ S&T Contributing Editor GOVERT SCHILLING lives in the
Netherlands but enjoys visiting astronomical facilities all over
the world. In August 2017 Harvard University Press will publish
his new book, Ripples in Spacetime: Einstein, Gravitational
Waves, and the Future of Astronomy.
s k y a n d t e l e s c o p e .c o m

* JUNE 2017

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Sky and Telescope - June 2017

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