119
See also: The Tychonic model 44–47 ■ Mapping southern stars 79 ■ Messier objects 87 ■ Space telescopes 188–95 ■
A digital view of the skies 296 ■ Roberts (Directory) 336 ■ Kapteyn (Directory) 337 ■ Barnard (Directory) 337
THE RISE OF ASTROPHYSICS
Gill applied clockwork tracking
mechanisms to telescope mounts
so that the telescope could move
in near-perfect harmony with the
rotation of Earth. This allowed the
instrument to remain fixed and
focused on a single patch of sky.
Gill was not the first to attempt
to photograph the heavens with
telescopes, but imaging faint
celestial light required exposures
of several minutes at least, and
poor tracking meant that early
star photographs were mostly
incomprehensible blurs.
Southern sky
In 1879, Gill became the chief
astronomer at the Cape Observatory
in South Africa. By now, he was
using the latest dry-plate system
(a photographic plate pre-coated
in light-sensitive chemicals), which
he employedto capture the “Great
Comet” that appeared over the
southern hemisphere in 1882.
Working in partnership with
the Dutch astronomer Jacobus
Kapteyn, Gill spent the best part
of the next two decades creating a
David Gill The eldest son of a successful
clockmaker, David Gill was
destined to take over the family
business. However, while at the
University of Aberdeen, he
became a student of the great
physicist James Clerk Maxwell,
whose lectures gave Gill a passion
for astronomy. When offered a job
as a professional astronomer in
1872, Gill sold the family business
and began work at the Dunecht
Observatory, Aberdeen.
In addition to his pioneering
work in astrophotography,
Gill developed the use of
the heliometer, a device formeasuring stellar parallax
(p.102). His measurements,
used in conjunction with his star
maps, did much to reveal the
distances between stars. By the
time he left the Cape Observatory
in 1906, Gill was a renowned
astronomer. In one of his final
jobs, the government consulted
him on the implementation of
daylight saving hours.Key work1896–1900 Cape Photographic
Durchmusterung (with
Jacobus Kapteyn)photographic record of the southern
sky. The result was the Cape
Photographic Durchmusterung
(catalog), showing the position
and magnitude of nearly half a
million stars. Gill also became
a key figure in the Carte du Ciel
(“Map of the Sky”) project, a global
collaboration of observatories
begun in 1887 with the goal of
making a definitive photographic
map of the stars. This ambitious,
expensive, and decades-long
project involved teams of human
computers who would measure
the plates by hand. It was, however,
superseded by new methods and
technologies before it was finished.
The accurate maps produced
by Gill’s photographic techniques
may seem fairly unremarkable
today, but at the turn of the 20th
century they were the first reliable
means for showing the properFrank McClean, an astronomer
friend of David Gill, donated the
McClean Telescope to the Cape
Observatory in 1897. David Gill
used it extensively.motion of nearby stars relative to
more distant ones. This information
was invaluable for measuring
stellar distances on a large
scale, and it began to reveal to
astronomers the true scale of the
galaxy and the universe beyond. ■