Astronomers think big all the time: it’s their job. And on 13th December, at
a meeting hosted by the Royal Astronomical Society in London, a group of
them will juggle with some truly astounding large numbers. On this occasion,
though, they won’t be discussing the distances to remote galaxies, but the
phenomenal sizes of the telescopes they want to build so they can explore
the universe to a level of detail previous generations of astronomers would
never have dreamt possible. Announcing a significant development, Professor
Gerry Gilmore of Cambridge University will tell the meeting that Europe’s
astronomers have just agreed to join forces in a single project to design a
new generation of ground-based optical/infrared telescopes, the Extremely
Large Telescope.

The largest telescopes operating currently (the two Keck Telescopes in
Hawaii) have segmented mirrors 10 metres across. Now, astronomers around the
world are working towards a giant leap for astronomy – ‘extremely large
telescopes’ (ELTs) up to 100 metres across, 10 times bigger than the Kecks.
According to Dr Adrian Russell, Director of the UK Astronomy Technology
Centre (UK ATC) in Edinburgh, a telescope that large will take up more glass
than has been used in all the telescopes built in the history of astronomy
put together.

In Europe, several projects have been under study for some years, each aimed
at identifying the key technological and organisational advances that must
be met to achieve such a big step . From this month, the two main projects –
Euro-50, led from Sweden, and OWL, led from the European Southern
Observatory (ESO) – are joining forces with colleagues throughout Europe to
create a single project, which will develop a proposal for substantial
additional funding from the European Union.

“An ELT facility will revolutionise astronomy with its ability to collect
light from faint objects and distinguish details in its images that have
never been seen before”, says Eli Atad who is Head of the Applied Optics
Group at the UK ATC and co-organiser of the meeting.

But ELTs are not just desirable, say astronomers: they are vital. The key to
understanding a remote astronomical object is its spectrum. Collecting
enough light to spread into a spectrum requires a much larger telescope than
recording an ordinary image. “The largest telescopes we have today are
struggling to obtain spectra of the faintest objects observable with the
Hubble Space Telescope,” says Dr Tim Hawarden, Project Scientist for ELTs at
the ATC and a speaker at the meeting. “Hubble’s successor, the James Webb
Space Telescope, begins operation in less than 10 years. It will discover
objects much fainter than Hubble can see and the problem of acquiring
spectra will get ten times worse. To make the most of discoveries with the
James Webb Space Telescope, it’s essential to have ELTs operating on the
ground at the same time.”

As is the case with the Keck Telescopes, the mirrors of the Extremely Large
Telescopes of the future will not be a single huge disc of glass, but will
consist of thousands of hexagonal glass ’tiles’. “The technology exists”,
says Eli Atad, “but the mass production of mirror segments is a challenge.”

“We have to prove that the key technologies are viable and affordable,” says
Gerry Gilmore, who chairs the steering committee for the new combined
European ELT project. “In particular, we have to demonstrate that the huge
number of components needed for an ELT can be built taking advantage of
industrial-scale efficiencies. The challenge is as much managerial and
industrial as it is technical. But it must be met if Europe’s astronomers
are to have the tools they need to keep abreast of international scientific
developments.”

“The potential payoffs from ELTs can fairly be described as awesome” says
Tim Hawarden. “For example, we may be able to see Earth-like planets, if
there are any, in orbit around stars up to tens of light years away, and
perhaps even find out what their atmospheres are made of. Just how large we
can make the new giant telescopes is still a matter for debate, and that is
part of what the meeting on 13th December is all about.”

CONTACTS

Dr Tim Hawarden, UK Astronomy Technology Centre, Royal Observatory
Edinburgh.
Phone: 0131 668 8339
e-mail: tgh@roe.ac.uk

Eli Atad, UK Astronomy Technology Centre, Royal Observatory Edinburgh.
Phone: 0131 668 8202 Mobile phone: 07718 737175
e-mail: ea@roe.ac.uk

Prof. Gerry Gilmore, Institute of Astronomy, University of Cambridge.
(Chairman of the Steering Committee for the European Large Telescope)
Phone: 01223 337506 Mobile phone: 07712 774522 Secretary 01223
766097
e-mail: gil@ast.cam.ac.uk

Dr Adrian Russell, UK Astronomy Technology Centre, Royal Observatory
Edinburgh. [Not available 9 – 13 December]
Phone: 0131 668 8313
e-mail: apgr@roe.ac.uk

NOTES

1. The Royal Astronomical Society Discussion Meeting on Friday 13th December
2002 takes place at the Scientific Societies Lecture Theatre, 23 Savile Row,
London W1, between 10.30 and 15.30. It is open to guests and the media. Full
details are available at:

http://www.roe.ac.uk/atc/ras2002/

2. The newly announced European project for an ELT now incorporates the
100-metre OverWhelmingly Large (OWL) Telescope concept led by the European
Southern Observatory (web site http://www.eso.org/projects/owl/) and the
Euro50 50-metre telescope concept led by the Lund Observatory, Sweden (web
site http://www.astro.lu.se/~torben/euro50/).

The two principal ELT projects in the USA are the Giant Segmented Mirror
Telescope (GSMT) (in the range 30-50 metres) at the National Optical
Astronomy Observatory, Tucson, USA (http://www.noao.edu/future/gsmt.html)
and the California Extremely Large Telescope (CELT), a 30-metre at the
California Institute of Technology (http://celt.ucolick.org/).

3. The UK expects to play a major role in the development of a European ELT
and will be providing scientific and engineering support in the
specification and design of the telescope and its instruments. There will
also be an opportunity for the UK to be involved in the manufacture of the
mirrors.

The manufacture of mirror segments will be a very different undertaking from
the specialised production of single large mirrors, which is expensive and
risky. Although designing and polishing the first mirror segment may be
difficult, once all the problems are solved, another 1000 units could be
turned out quickly and cheaply (and profitably). Similarly, instruments for
the telescope may require numerous modular sub-systems which, once
developed, could be manufactured on a commercial scale.

4. The UK Astronomy Technology Centre is located at the Royal Observatory,
Edinburgh (ROE). It is a scientific site belonging to the Particle Physics
and Astronomy Research Council (PPARC). The mission of the UK ATC is to
support the mission and strategic aims of PPARC and to help keep the UK at
the forefront of world astronomy by providing a UK focus for the design,
production and promotion of state of the art astronomical technology.

The Royal Observatory, Edinburgh comprises the UK Astronomy Technology
Centre (UK ATC) of the Particle Physics and Astronomy Research Council
(PPARC), the Institute for Astronomy (IfA) of the University of Edinburgh
and the ROE Visitor Centre.