David Stanley Evans died on November 14, 2004, in Austin, Texas. He is survived
by his wife, Betty Hall Evans, and sons, Jonathan Evans of Nashville, Tennessee,
and Barnaby Evans of Austin, Texas. He had six grandchildren, three in Nashville,
and three in Austin. David was a noted observational astronomer whose career
was divided between South Africa and Texas. He also used the extensive historical
collections at this University to write several books on the history of astronomy.
He was born in Cardiff, Wales, on January 28, 1916. David received his B.A. degree
in mathematics in 1937 from Kings College, Cambridge. He became a Ph.D. student
at Cambridge Observatory in 1937 and was one of Sir Arthur Eddington’s
last surviving students. He received his Ph.D. degree in 1941 with a dissertation
entitled “The Formation of the Balmer Series of Hydrogen in Stellar Atmospheres.” He
was a conscientious objector to war and, thus, spent the war years at Oxford
working with physicist Kurt Mendelssohn on medical problems, involving cadavers,
relating to the war. During these years, David was scientific editor of
Discovery and
he was editor of
The Observatory.
David left England in 1946 in order to take up the position of second assistant
at the Radcliffe Observatory, Pretoria, South Africa. He and H. Knox Shaw were
the entire staff, after R.O. Redman left, and they aluminized and installed the
mirrors in the 74-inch telescope. His notable scientific contribution was to
use lunar occultations to measure stellar angular diameters during the 1950s.
In addition, he succeeded in determining the angular diameter of Antares and
determined that Arcturus was not circular but had an elliptical shape. The elliptical
shape was later shown to be an instrumental artifact, but the utility of using
lunar occultations to measure stellar diameters and stellar multiplicity was
conclusively demonstrated. T. Gold presented David’s paper on lunar occultation
angular diameters at the January 1953 meeting of the Royal Astronomical Society.
David felt resentment at Gold’s remarks, which lasted all David’s
life because he felt that he was ridiculed. By this time, David Evans was chief
assistant at the Royal Observatory headquartered in Cape Town, South Africa.
David designed and had built a Newtonian spectrograph for the 74-inch Radcliffe
Telescope with which he measured the first southern galaxy redshifts.
David and his family spent 1965-66 in Austin, Texas, where he was a National
Science Foundation Senior Visiting Scientist at The University of Texas and McDonald
Observatory. They moved permanently to Austin in 1968, and David became a professor
of astronomy and associate director of McDonald Observatory at The University
of Texas at Austin.
At McDonald Observatory, R. E. Nather devised a high-speed photometer capable
of measuring millisecond time-scale changes in brightness, and with Brian Warner,
they invented “high-speed astronomy.” This instrument caused Evans
to revive his occultation program and, over the next 20 years, he produced the
major part of the angular diameters of late-type stars with his students and
collaborators. In addition, David and collaborators used the extensive collections
of The University of Texas to write “Herschel at the Cape,” and David
was involved in observing the occultation of b Sco by Jupiter in 1972 and in
observing the gravitational deflections in the positions of stars whose light
passes near to the Sun during a solar eclipse in 1973. The eclipse was observed
from Maurtania and the observations confirmed Einstein’s prediction again.
David Evans and his students studied late-type stars, which have large star-spots,
and others, which flare. In addition, they studied stars whose lunar occultation
observations had revealed to be double and some with more than two stars. David
Evans’ major scientific contribution was an application of his stellar
angular diameters to deduce the surface brightness of stars. With suitable color,
the result was indices one could use photometry to deduce the angular diameter
of stars. This is applicable to stars which can never be occulted by the Moon,
and its application to Cepheid variable stars has yielded their distances. This
relation between angular diameters and a V-R color index is called the Barnes-Evans
Relation. Although Tom Barnes gives most of the credit to Evans, he said that
David insisted that the authors be listed in alphabetical order. This work was
greeted with initial skepticism, but it stimulated an enormous amount of interest
and has been used to measure distances to 100 Cepheid variable stars in our galaxy.
The method gives a distance to one of them, Delta Cephei, which agrees closely
with recently measured parallaxes using HST. The Barnes-Evans method yields distances
which are accurate to a few percent and is applicable to Cepheids in nearby galaxies.
Before coming to Texas, David Evans had never given a large lecture course at
a university, and his efforts met with mixed success especially in introductory
classes for freshmen facing a “science requirement.” David had considerable
more success supervising Ph.D. dissertations, and he was surpervisor for four.
He was promoted to the position of Jack S. Josey Centennial Professor of Astronomy
in 1984, which is the position he held until his retirement in 1986. He was awarded
the Gill Medal of the Astronomical Society of South Africa in 1988.
David Evans had a remarkable facility for language, especially English. He was
an author of eight books including a 1966 edition of
Teach Yourself Astronomy, which
was an introduction to astronomy and an inspiration to a number of currently
active astronomers. He also loved history, especially of Southern Hemisphere
astronomy but including McDonald Observatory.
David was a squash player into his 80s, and as his physical abilities declined,
he became more devious. He would burst into song at the top of his lungs, sometimes
in English and sometimes with a slightly bawdy version of a Christmas carol.
He did this without any sign of being self-conscious. This astronomer, who began
his academic life as a precocious mathematical genius, became self-conscious
in his later years as to the value of his scientific career and the wisdom of
his earlier decision to be a conscientious objector. In fact, David continued
to be very active after retirement, and when he died, he had completed a book
(with Karen Winget) on the eclipse expedition to Mauratania, which is not yet
printed.
<signed>
Larry R. Faulkner, President
The University of Texas at Austin
<signed>
Sue Alexander Greninger, Secretary
The General Faculty
