Sky & Telescope - February 2024 - 6

LOWELL OBSERVATORY ARCHIVES
FROM OUR READERS
Vesto Slipher and Edwin Hubble
In " Vesto Slipher's Fast Stars and Hotrod Galaxies " (S&T:
Sep. 2023, p. 20), Douglas MacDougal rightly characterizes
Slipher's discovery of the redshifts of spiral nebulae as " one of
the most fundamental discoveries in the history of science, "
and the first evidence of the expanding universe. Slipher's
achievement, however, has never been commemorated.
This is owed partly to Edwin Hubble. In his landmark 1929
paper in Proceedings of the National Academy of Sciences (Vol. 15,
p. 168), establishing the linear relationship between Slipher's
radial velocities and Hubble's distances, Hubble failed to cite
Slipher's 1913-1925 publications or even mention his name!
Perhaps realizing this ethical breach, he did credit Slipher in
ensuing years, but it was still dubbed solely " Hubble's law. "
At the General Assembly in 2018, the International Astronomical
Union adopted a resolution renaming it the " HubbleLemaître
law, " to honor Georges Lemaître, who in 1927 had
predicted the expansion of the universe through Einstein's
general theory of relativity. They rejected any Slipher eponym
on the rationale that a " law " should be based on theory.
As a workaround, we propose that the IAU consider renaming
the separate " Hubble constant " - the observed velocitydistance
proportionality - the " Hubble-Slipher constant. "
Hubble himself provided the rationale: While writing to
Slipher in 1953, he praised Slipher's " first steps as by far the
most important of all " in " the combination of your velocities
and my distances . . . " Slipher worked alone gathering these
critical early radial velocities. He deserves this honor.
Joseph N. Marcus
Lowell Observatory Advisory Board
St. Louis, Missouri
Marcia Bartusiak
Professor of the Practice Emeritus
Massachusetts Institute of Technology
Cambridge, Massachusetts
Douglas MacDougal responds: The extent of Hubble's
reliance on Slipher's work is shown in a letter to Slipher
dated July 8, 1940, in Lowell Observatory's archives. There Hubble
asks Slipher to confirm details of " your now famous list of velocities "
for a catalog Hubble was creating. The list, in Hubble's hand, is
headed " Slipher's Velocities " and contains the " list of your [Slipher's]
velocities as we know them. " Even the casual researcher can't fail to
notice the mirror-like match-up of the Slipher's Velocities to those in
Hubble's 1929 paper. In fact, 40 of the 44 galaxies cited by Hubble
came from Slipher.
"
The historic velocity-distance graph in Hubble's 1929 paper, and
the " Hubble constant " derived from its slope, was thus apparently
built in halves: The vertical axis (of velocities) properly belongs to
Slipher, and the horizontal axis (of distances) belongs to Hubble.
Arguably more important even than the quantifiable extent
of Hubble's reliance upon Slipher's data, though, was Slipher's
paradigm-smashing idea that there could be such a universe of
6
FEBRUARY 2024 * SKY & TELESCOPE
receding galaxies. This completely new and revolutionary aspect
of our cosmos was entirely due to Slipher. Marcus and Bartusiak's
proposal is a welcome recognition of these facts.
I am an avid reader of Sky & Telescope. My husband and I keep
a close watch on sky activity, as we live in a dark-sky area of
rural Texas. Our visitors are constantly amazed to see the
Milky Way in its full glory! I don't own a telescope, so I often
breeze over the telescope articles in the magazine, but I love the
articles on the science of new discoveries and theories. However,
my favorite articles are the historical ones. In the September
2023 issue, you had two great articles, " Vesto Slipher's Fast
Stars and Hotrod Galaxies " by Douglas MacDougal on page
20 and " Hubble's Eureka Moment " by Dave Tosteson on page
26! Learning the history of how we got to where we are in our
knowledge base is fascinating. I am especially enthralled when
you have articles about ancient sky observers.
Keep up your great work on covering articles for everyone's
interests!
Barbara Barnes
Junction, Texas
p Edwin Hubble wrote this letter to V. M. Slipher asking for copies of the
spectra Slipher took that best represented the redshift of galaxies for his
lecture. Hubble built his famous theory on Slipher's studies of redshift.
Sky & Telescope - February 2024

Table of Contents for the Digital Edition of Sky & Telescope - February 2024
