When you are trying to make very accurate, high speed measurements of the
optical radiation from the Sun’s corona (atmosphere) — in order to determine
why it is so much hotter than the Sun’s surface — a total eclipse of the Sun
offers an ideal, if extremely brief, opportunity. This is what Professor Ken
Phillips has done for the last three solar eclipses, and he’s just returned
from the most recent — in southern Africa on Thursday 21 June.

“I was leading a team of seven scientists for this eclipse, two from CLRC
Rutherford Appleton Laboratory (including me), three from Queen’s University
in Belfast and two from the University of Wroclaw in Poland, where some of
the equipment was made. We had been offered room on the roof of the Physics
Department at the University of Zambia near Lusaka by Dr Habatwa Mweene,
Head of the Physics Department, and the SECIS (Solar Eclipse Coronal Imaging
System) equipment was set up there,” said Ken.

The equipment consists of a pair of fast-frame CCD cameras, capable of
operating at frame rates up to 60 or 70 per second, plus a small telescope
and optics. This telescope includes a ‘green line’ filter (there is a bright
spectral line due to Fe XIV (an ion of iron) in the coronal spectrum that
this filter isolates) and a tracking mirror. This makes SECIS one of the
fastest and most sophisticated astronomical digital cameras.

“We need this speed and sophistication to record subtle changes in the corona.
We are almost certain that the magnetic fields, which are abundant in the
Sun’s atmosphere, are involved in the heating process, but scientists are
intrigued to find out exactly how the process works,” explains Ken. “When
we arrived the weather was overcast and uninspiring, but by the day of the
eclipse it had improved to offer ideal, cloudless conditions. There was a
tremendous air of excitement among local people who had gathered at the
University on various days throughout the week before. I gave a talk to 700
extremely enthusiastic youngsters and their teachers on 19 June, and it was
thrilling for me to tell them about the eclipse and describe what they should
look for — they only vague impressions from newspaper and magazine reports.
Unfortunately there was a desperate shortage of eclipse viewers and there
were rumours that they were changing hands at £20 a time!”

Leading up to the eclipse images from both the TRACE and SOHO spacecraft
clearly showed a new region rotating round on the sun’s NE limb with
associated prominences. The SECIS instrument does not view the whole corona,
and seeing images from the spacecraft was important for the team to decide
where to point the instrument. Both the CDS (one of the instruments on the
SOHO satellite) experiment and instruments on the TRACE spacecraft were
supporting the eclipse with images of the new region on the NE limb.

“I was extremely pleased not only to see the eclipse (my third, all under
ideal weather conditions) but also to see the images coming up on our
computer monitor during totality that showed everything was functioning
well. It was a great moment,” said Professor Phillips.

The team was filmed ‘fly on the wall’ style by John MacNish from Cirlevision
who is putting together a BBC2 TV programme called Final Frontier. This will
be screened on July 5 (starting half an hour after midnight) and repeated
the following Sunday morning (at 7.45am) and might be screened the following
Wednesday.

“I hope no embarrassing things will be shown!”, commented Ken. The project
was funded through the Particle Physics and Astronomy Research Council
(PPARC), the Leverhulme Trust and Queen’s University Belfast, as well as
the FTS fund in 1997 which enabled us to buy the cameras. CLRC also provided
financial help.

“I hope we will be able to capitalise on the enormous amount of data SECIS
has collected. The heating of the sun’s corona (and by implication of the
coronae of all solar-type stars) is still unclear, so we hope that the data
we collected over the last two eclipses will help us understand the question
a lot better,” said Ken.

Checkout the SECIS web pages at http://www.SECIS.rl.ac.uk/ for further
information about the project.