100
A SURVEY OF THE
WHOLE SURFACE
OF THE HEAVENS
THE SOUTHERN HEMISPHERE
IN CONTEXT
KEY ASTRONOMER
John Herschel (1792–1871)BEFORE
1784 Charles Messier
publishes a list of 80
known nebulae.AFTER
1887 The Cartes du Ciel, an
ambitious project to survey
the entire sky photographically,
is initiated by the director
of the Paris Observatory,
Amédée Mouchez.
1918 The Henry Draper
Catalog, covering most
of the sky, is published by
Harvard College Observatory.1948–58 The Palomar
Observatory in California
completes its major sky
survey, which includes
data from nearly 2,000
photographic plates.1989–93 The Hipparcos
satellite gathers data that
allow more than 2.5 million
stars to be cataloged.B
etween 1786 and 1802,
William Herschel published
catalogs listing more
than 1,000 new objects in the
night sky. Following his death in
1822, William’s son John continued
his work, but expanded its scope
and ambition to carry out a
complete survey of the night sky.
William’s observations had all been
made from southern England, and
so were limited to objects down
to around 33° below the celestial
equator. To survey the rest of thesky, his son’s observations would
have to be made from somewhere
in the southern hemisphere.
Herschel settled on South
Africa, then a part of the British
Empire. He moved there in 1833,
taking with him his wife and
young family, an assistant, and
his father’s 20-ft (6-m) focal length
telescope. This was the same
instrument that had been used
to survey the northern skies,
and Herschel chose it to ensure
that the new information gathered
from the southern hemisphere
was comparable to that already
produced. The family set
themselves up in a house near
the base of Table Mountain, far
enough away to avoid the clouds
that often gathered on its summit,
and Herschel spent the next four
years completing his survey.The southern skies
The Magellanic clouds are two
dwarf galaxies close to the Milky
Way, and are only visible from the
southern hemisphere. They can beThe Milky Way’s core is clearest
from the southern hemisphere. The
dark regions are where starlight is
blocked by interstellar dust.