Sky & Telescope - April 2024 - 58

POSS-II / STSCI / CALTECH / PALOMAR OBSERVATORY
APRIL 2024 OBSERVING
Going Deep by Steve Gottlieb
NGC 4075
UGC 7034
CGCG 13-49
NGC 4073
PGC 38205
CGCG 13-58
NGC 4139
NGC 4077
CGCG 13-52
NGC 4063
NGC 4045
NGC 4045A
TODD'S TARGETS In his search for a planet
beyond Neptune, American astronomer David
Todd discovered numerous faint galaxies. He
also missed some. Use the image at left to
locate the galaxies described in the text.
reference star and came up empty. Ferguson
took up the search but also failed
to retrieve it, leading to speculation it
might instead be an unknown planet.
In 1878, asteroid hunter Christian
Heinrich Friedrich Peters solved the
mystery of the missing star. A mislabeled
micrometer wire caused Ferguson
to measure an errant position. By this
date, however, the prospect of a transNeptunian
world had captured other
astronomers' imaginations.
Todd reanalyzed the residuals for
UGC 7057
David Todd's Accidental
Deep-Sky Discoveries
While searching for a distant planet, this American astronomer
stumbled upon several galaxies in Leo and Virgo.
O
n February 6, 1878, David Peck
Todd discovered the 14th-magnitude
galaxy IC 591 using the U.S. Naval
Observatory's 26-inch Clark refractor.
The galaxy's location is surprising,
just 23′ northwest of 1.4-magnitude
Regulus, or Alpha (α) Leonis. But Todd
wasn't seeking new nebulae - his aim
was to discover a planet beyond Neptune!
He conducted a little-known
visual search and, as we'll see, in the
process dug up some intriguing galaxies.
Todd wasn't the first to predict a
new, distant planet. In 1848, just two
years after the discovery of Neptune,
58 APRIL 2024 * SKY & TELESCOPE
French scientist Jacques Babinet proposed
a trans-Neptunian planet. He
arrived at this conclusion by analyzing
perturbations in Neptune's motion
using the predicted orbital elements
by French mathematician Urbain Le
Verrier and English astronomer John
Couch Adams. Babinet dubbed the
unseen world Hyperion.
Two years later, James Ferguson, an
astronomer at the Naval Observatory,
measured the asteroid Hygiea's position
relative to a nearby 9th-magnitude star.
English astronomer John Russell Hind
created a stir when he looked for the
the positions of Uranus and Neptune
in 1877. His calculations pointed to
a trans-Neptunian planet of magnitude
13 or fainter at a distance of 52
astronomical units (a.u.). Based on an
expected longitude of 170°±10°, Todd
began a visual search in Leo on November
3, 1877. He carefully examined each
field at 400× to 600×, covering 40°
along the ecliptic, and checked any nonstellar
objects for movement. The project
ended unsuccessfully on March 6, 1878.
Did he stand a chance in his pursuit?
As far as stumbling upon Pluto, it was
in Taurus at the time, a full 14° south
of the ecliptic and far beyond his search
region. Furthermore, he was looking
for a tiny but distinct disk, estimated
at 2.1″ in diameter. Pluto, of course,
appears stellar in a telescope.
So, what did he find? A modern
analysis shows Todd netted 28 galaxies,
including several previously known.
Many others, though, were unidentified,
as his rough positions using the
refractor's setting circles landed on
empty patches of sky. But by reviewing
his sketches and positional offsets from
nearby stars, catalog sleuths Harold
Corwin, Wolfgang Steinicke, and others
(including myself) recovered 16 of the
28 as original discoveries.
" Suspected Object "
Let's examine the evidence for IC 591,
which Todd described as a " Suspected
object faint and diffused. " A finder
Sky & Telescope - April 2024

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