Sky & Telescope - January 2022 - 60

TELESCOPE: J. PASS / WIKIMEDIA COMMONS / PUBLIC DOMAIN; SCORPIUS: COLLECTION OF
JAY AND NAOMI PASACHOFF, COURTESY WAYNE HAMMOND / WILLIAMS COLLEGE'S CHAPIN LIBRARY
Celestial Cartography
search for deep-sky treasures. When did a suitable set of
charts first appear? We can't know to what extent astronomers
of the 17th to 19th centuries relied on star atlases in their
quest to explore the heavens, but we can certainly determine if
any of those available would be helpful to today's amateurs.
Bode and Uranographia
One obvious candidate is the wonderful Uranographia, which
was produced by the German astronomer Johann Elert Bode.
Published in 1801, Uranographia represents the high point
of celestial cartography's marriage of art and science, which
soon thereafter parted ways. Later works that featured artistic
depictions of the constellations never matched the astronomical
accuracy of Bode's masterpiece - those atlases that
focused on the science of the heavens generally abandoned
fanciful constellation figures altogether.
Uranographia contained very large charts (31 by 23 inches,
or 79 by 58 cm) and used special symbols and Roman numerals
to plot deep-sky objects and indicate their appearance.
Bode included more than 2,000 nebulae and hundreds of
double stars based on the observations of British astronomer
William Herschel, who surveyed the heavens in the late 18th
century from England with reflector telescopes of 6, 12, 18.7,
and (ultimately) 48 inches in aperture.
Herschel categorized deep-sky objects as follows:
I
II
Bright nebulae
Faint nebulae
III Very faint nebulae
IV Planetary nebulae
V
Very large nebulae
VI Very compressed and rich clusters of stars
VII Compressed clusters of faint and bright stars
VIII Coarsely scattered clusters of stars
THE BEAST OF
SLOUGH British astronomer
William Herschel
discovered more
than 2,000 deep-sky
objects using several
telescopes, the largest
of which was this
monster with a 48-inch
(122-cm) aperture and
" forty-foot " focal length
erected in Slough,
England. It ceased
operation in 1815.
Bode's charts were the first to incorporate these designations,
and they persisted in modern works, including many
editions of Norton's Star Atlas.
Modern-day amateurs clearly could use Uranographia, even
though the giant atlas might be somewhat unwieldy, to locate
double stars and deep-sky objects. But was it the first such
work? Bode himself created a smaller version in 1782, and
other celestial cartographers produced earlier efforts. Could
one of these take the prize instead? To answer this, it's helpful
to decide what a deep-sky atlas should be.
Here are the features that I consider most important: First,
the charts should be reasonably detailed - every observer
knows the frustration of trying to find targets when there
aren't enough stars presented, or the chart scale is too small.
Second, the atlas should include dozens of deep-sky objects,
represented with symbols that make them easy to distinguish
from stars. Third, the atlas should be as error-free as possible,
with a minimum number of " false nebulae " to mislead users.
Fourth, each chart should cover a small enough area of sky
to avoid severe projection distortion at the edges. And finally,
the charts should use an equatorial coordinate system and
not some other, less useful scheme.
Discovering the Deep Sky
Of course, for an atlas to feature deep-sky objects, those
objects first have to be discovered and cataloged. Lists of nebulae
were usually compiled by adding new discoveries to previously
known ones. Progress was slow. Only 19 such objects
were widely known prior to 1700, and by 1750 that total had
increased to just 35. In 1755, French astronomer NicolasLouis
de Lacaille tabulated 42 objects that included 24 new
finds. Working from the Cape of Good Hope in South Africa,
Lacaille made discoveries that were out of reach for European
observers. In 1771, French comet hunter Charles Messier presented
the first installment of his now-famous catalog, which
included 45 entries - many of which he discovered.
Bode himself produced a list of 75 objects in 1777, but he
EARLY NEBULAE Johannes Hevelius's 1687 atlas was the first to
show the open cluster M7 (indicated) in the correct location. The cluster
was misplotted by Gallucci in 1588, and it appears that Bayer (1603) and
Schiller (1627) may have simply perpetuated Gallucci's error.
60 JANUARY 2022 * SKY & TELESCOPE
only discovered 5 of these and, according to Kenneth Glyn
Jones in his book The Search for the Nebulae (1975), Bode's
selection " contains far too many errors and misprints and
one of the worst features is that the list is greatly inflated by
numerous asterisms and 'non-objects.' "
Sky & Telescope - January 2022

Table of Contents for the Digital Edition of Sky & Telescope - January 2022
