Sky and Telescope - November 2015 - 49

Richard Jakiel observes the solar system and deep space from his home,
"Mars House," in the wilds of suburban Atlanta, Georgia.

Richard Jakiel

The Moon * November 2015
Librations

Distances
Apogee
252,103 miles
Perigee
225,444 miles

November 7, 22h UT
diam. 29′ 16″
November 23, 20h UT
diam. 32′ 55″

Phases

Poncelet (crater)
Byrd (crater)
Petermann (crater)

November 23

LAST QUARTER

November 3, 12:24 UT

November 23
November 25
November 27

25
27

NEW MOON

November 11, 17:47 UT
FIRST QUARTER

November 19, 6:27 UT
FULL MOON

November 25, 22:44 UT
For key dates, yellow dots indicate
which part of the Moon's limb is
tipped the most toward Earth by
libration under favorable illumination.

Sk yandTelescope.com November 2015

NASA / LRO

as large as the third satellite [Ganymede] appears."
He added that they traveled in close proximity to one
another, with four of the ﬁve in a co-latitudinal line.
The three smaller spots were the size of Europa (about
1 arcsecond across). More spots appeared over the next
3 months, until 11 of them were spread around the
planet. Dawes was the ﬁrst to note changes in the relative velocity of the spots, as those lower in latitude traveled faster around the planet.
Perhaps his most signiﬁcant Jovian discovery was
made on November 27, 1857. His drawings from that
night record a series of disturbances and spots in the
southern hemisphere. One sketch includes a large
oval region that was about to rotate behind the planet.
This represents one of the earliest observations of the
structure now known as the Great Red Spot Hollow.
(Not until 1878 would American astronomer Carr Walter
Pritchett make the ﬁrst well-documented appearance of
the Great Red Spot itself.)
Dawes was never a robust man, and his health took
a decided downturn in the 1860s. Still, along with
numerous double-star measurements, he completed a
series of remarkable drawings of Mars during its 1864
opposition and made detailed observations of the Leonid
meteor storm on the night of November 13-14, 1866. In
recognition of his many accomplishments, he was made
a Fellow of the RAS in 1865. With his health failing, he
still managed to observe a second occurrence of "Jupiter
without satellites" on August 21, 1867. Unlike the 1843
event, this one was widely seen by observers across the
European continent.
With his trusty 8-inch Clark at 412×, that evening
Dawes observed the transits of Io, Ganymede, and Callisto plus their shadows, while Europa remained hidden
behind Jupiter. He found Ganymede particularly interesting, and the sketch he submitted to the RAS shows
darker terrain covering almost half of its surface. These
and other details proved to be a good follow-up to the
Galilean satellite observations he made in 1849-50.
On February 15, 1868, less than six months after
witnessing his second moonless event, William Rutter
Dawes passed away. But "Eagle-Eyed Dawes" left a rich
legacy of careful observations that qualify him as one of
the pioneers of planetary science. ✦

JOHN G. WOLBACH LIBRARY (2)

Right: Dawes' engravings from 1849 and 1860 show bright and
dark details on Jupiter's "third satellite" (Ganymede) and a
relatively featureless "fourth satellite" (Callisto). Lower right: On
November 27, 1857, Dawes apparently became the ﬁrst observer
to record the Great Red Spot Hollow (though not the spot itself)
as a large oval area at upper left on the disk. He made this
observation at 8:10 Greenwich Mean Time, which in that era corresponded to 8:10 p.m. in England. South is up in both panels.

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Sky and Telescope - November 2015

Table of Contents for the Digital Edition of Sky and Telescope - November 2015