My first Magazine Sky & Telescope - 01.2019 | Page 23

bluish rim to the umbra produced a beautiful
‘diamond ring’ effect, and caused some observ-
ers to wonder if the eclipse was really total.”
Conversely, on rare occasions the Moon
0
has almost completely vanished from view, the
direct result of major volcanic eruptions on our
planet. It is well known that dust suspended in
Dark eclipse, gray
or brownish in
our atmosphere affects the amount of sunlight
coloration. Lunar
that is refracted into Earth’s umbra. In 1963
features are dis-
debris from the explosion of Mount Agung in
tinguishable only
Bali caused the Moon to be nearly invisible
with diffi culty.
1
during totality, and in 1982 and 1991, respec-
tively, the eruptions of El Chichón in Mexico
Deep red or rust-
and Mount Pinatubo in the Philippines were
colored eclipse.
later followed by lunar eclipses that also were
Very dark toward
exceedingly dark.
center of umbral
shadow, though
Last July 27th, the Moon tracked just north
relatively bright at
of the center of Earth’s shadow, resulting in
2
its outer edge.
an especially long totality lasting 103 minutes.
One might have assumed that such circum-
Brick-red eclipse.
stances would result in an abnormally dark
Umbral shadow
eclipse. But observers reported that, while the
usually has a
Moon perhaps appeared somewhat dimmer
fairly bright gray
or yellow rim.
than normal, overall it was not an exception-
3
ally dark event.
Sky brightness: In just over an hour, the
brightness of the sky will change dramatically.
Very bright
copper-red or
Before the eclipse begins, brilliant moonlight
orange eclipse.
will wash out all but the brightest stars. But
Umbral shadow
during totality, chiefl y from rural locations,
has a bluish, very
the winter Milky Way and myriad fainter stars
4
bright rim.
will appear. Gemini’s “twins,” Pollux and
Castor, will be a dozen degrees northwest of
p HOW DARK IS DARK? Use
the darkened Moon, while the famous Beehive
this ive-step Danjon scale to
Cluster in Cancer lies 7° to the east. Although
judge the darkness of the totally
all but impossible to spot prior to the start of
eclipsed Moon.
the eclipse, during totality the cluster should be
relatively easy to see with the unaided eye. In fact, the Bee-
hive’s pairing with the darkened Moon will make for a striking
2019
sight through wide-fi eld binoculars.
Sometimes during totality observers catch the occultation
AST
of a relatively bright star by the umbra-immersed lunar disk
or even a dramatic graze along one of the lunar poles. Not so
11:10 p.m.
this time: Only three stars brighter than magnitude 9.0 will be
11:34 p.m.
occulted during January’s event.
12:41 a.m.
One advantage of a total lunar eclipse, compared to its
solar counterpart, is that it’s a leisurely affair. In short, should
1:12 a.m.
the weather cooperate on the third Sunday night in January,
1:44 a.m.
there will be plenty to see and do. Good luck and clear skies!
Totality this year will last a bit longer than
average: 62 minutes. The Moon will pass north
of the center of Earth’s shadow, so during the
total phase the upper part of the Moon will
appear brighter while its lower portion should
look noticeably darker and more subdued.
In recent years, the mainstream media
have been branding total lunar eclipses as
“Blood Moons.” But this is a misnomer, for
the umbra-covered Moon does not always
have a reddish glow. The colors that appear on
the Moon solely depend on the state of our
atmosphere, a turbulent mélange of clouds
and volcanic dust and other contaminants,
so it’s hard to say in advance exactly how the
totally eclipsed Moon might look.
Darkness of totality: In fact, there can be
a wide range in the brightness of the Moon
from one total eclipse to the next. So will this
be a dark eclipse or a bright one, compared
to others? In 1921, the French astronomer
André-Louis Danjon introduced a five-point
scale of luminosity (L) to classify total lunar
eclipses; the scale’s steps are shown at right.
This rating is preferably made near mid-
totality with the unaided eye. If you can’t
decide between two L values, say, 1 and 2,
split the difference and call it 1.5. I’d like to
know your result, so please send your estimate
to [e-mail]. Be sure to state the
time and the optical means used, if any.
During very bright eclipses, the Moon can
resemble a bright copper penny. More than a
half century ago (October 1967), an eclipse
was so vivid that one California amateur’s
report to Sky & Telescope noted, “A bright
Eclipse of January 20–21,
MST CST EST 8:10 p.m. 9:10 p.m. 10:10 p.m. 8:34 p.m. 9:34 p.m. 10:34 p.m. 9:41 p.m. 10:41 p.m. 11:41 p.m. 10:12 p.m. 11:12 p.m. 12:12 a.m. 10:44 p.m. 11:44 p.m. 12:44 p.m. 11:51 p.m. 12:51 a.m. 1:51 a.m. 2:51 a.m.
12:15 a.m. 1:15 a.m. 2:15 a.m. 3:15 a.m.
Very dark
eclipse. Moon
almost invisible,
especially at
mid-totality.
¢ A veteran of 18 total lunar eclipses, S&T Contributing Edi-
tor JOE RAO has served as an Associate at New York City’s
Hayden Planetarium for more than 30 years. He’s an eight-time
Emmy-nominated broadcast meteorologist at Verizon FiOS1
News in New York’s Lower Hudson Valley.
sk yandtele scope.com • JA N UA RY 2 019
21