120
A PRECISE
MEASUREMENT
OF THE STARS
THE STAR CATALOG
IN CONTEXT
KEY ASTRONOMER
Edward C. Pickering
(1846–1919)BEFORE
1863 Angelo Secchi develops
spectral classification for stars.1872 American amateur
astronomer Henry Draper
photographs the spectral
lines of Vega.1882 David Gill begins to
survey the southern sky
using photography.AFTER
1901 Annie Jump Cannon,
along with Pickering, creates
the Harvard Classification
Scheme, which forms the
basis of stellar classification.1912 Henrietta Swan Leavitt
links the period of Cepheid
variables to their distance.1929 Edwin Hubble
measures the distance
to nearby galaxies using
Cepheid variables.E
dward C. Pickering, in his
role as director of the Harvard
College Observatory from
1877 to 1906, laid the foundations
for precise stellar astronomy. His
team carried out star surveys that
broke new ground in understanding
the scale of the universe. Pickering
combined the latest techniques in
astrophotography with spectroscopy
(splitting light into its constituent
wavelengths) and photometry
(measuring the brightness of stars)
to create a catalog that listed
a star’s location, magnitude, and
spectral type. He did this with thehelp of the Harvard “computers”—
a team of mathematically
minded women upon whom
Pickering relied to process the
huge amounts of data required
to create the catalog.
More than 80 computers,
known in those less enlightened
days as “Pickering’s Harem,”
worked at the Harvard Observatory.
The first of them was Williamina
Fleming, who had been Pickering’s
maid. Upon taking over the
observatory, Pickering fired his
male assistant, deeming him
“inefficient,” and hired Fleming
in his place. Other notable names
among the computers included
Antonia Maury, Henrietta Swan
Leavitt, and Annie Jump Cannon.Color and brightness
Pickering’s individual contributions
to the star catalog were twofold. In
1882, he developed a method of
photographing multiple star spectra
simultaneously by transmitting the
stars’ light through a large prism
and onto photographic plates.
In 1886, he designed a wedge
photometer, a device for measuring
the apparent magnitude of a star.
Magnitudes had previously been
recorded psychometrically—usingA woman had no chance
at anything in astronomy
except at Harvard in the
1880s and 1890s. And even
there, things were rough.
William Wilson Morgan
US astronomer