Sky & Telescope - March 2024 - 49

West
LEAH TISCIONE / S&T, SOURCE: FRED ESPENAK
East
within 3° of Jupiter. While 12P will glow
brightest at that time (possibly reaching
4th magnitude), it will also be a challenging
target, hovering low in the western
sky in twilight. But who knows? More
outbursts are likely in the cards, adding a
dash of unpredictability to forecasts.
Northern observers will lose sight of
the comet in late April, but for observers
in the Southern Hemisphere the comet
remains in view low in the western sky
well into August as it arcs from Taurus
into Vela and beyond. Perihelion occurs
on April 21st followed by its closest
approach to Earth on June 2nd, when
it's 1.5 a.u. (220 million km) distant.
Periodic comets like this can transport
us back to an earlier era of astronomy,
making a connection that enriches
the observing experience. French
astronomer Jean-Louis Pons discovered
the object in July 1812, and then it was
recovered by American astronomer William
Brooks in September 1883. Both
were prolific comet-finders - Pons still
holds the record for the most visual
comet discoveries at 37. Although it
bears the Pons and Brooks names,
records of prior appearances date back
centuries. Early observers logged the
comet in 1385 and 1457 and perhaps as
long ago as 245.
At its most recent previous
apparitions in 1883-84 and 1953-54,
the comet also experienced dramatic
flares. The cause of these spectacular
fits may be the same as the one that
powers the frequent outbursts from
Comet 29P/Schwassmann-Wachmann.
Rapid outgassing of carbon monoxide
and carbon dioxide from the comet's
core occurs when heat from the Sun
fractures the overlying crust, expelling
millions of tons of fresh ice and dust.
The sudden release of so much material
into the light of day temporarily boosts
the comet's brightness, making it
appear as if a bomb has exploded. The
debris cloud gradually expands and
fades until the next blowup recharges
the coma with fresh material. To keep
track of 12P and its delightfully erratic
behavior, visit the Comet Chasers
website at cometchasers.org/home/
comet-12p-observations.
Penumbral Lunar Eclipse
March 25, 2024
North
Moon
enters
penumbra
(unobservable)
4:53 UT
Mideclipse
7:13
UT
Moon
leaves
penumbra
(unobservable)
9:33 UT
B
South M
A Deep
Penumbral
Lunar Eclipse
PENUMBRAL ECLIPSES tend to get
overlooked. But I'd encourage you to
catch the one happening the night of
March 24-25 for two reasons. First,
solar and lunar eclipses always come
in pairs separated by about two weeks.
This particular event makes a delicious
appetizer for the highly anticipated
April 8th total solar eclipse. Second,
despite the eclipse's penumbral designation,
this will be a deep penumbral
eclipse with Earth's shadow readily visible
to the naked eye.
In a partial or total lunar eclipse,
the Moon dips into Earth's umbra, or
inner shadow, where our planet's globe
blocks direct sunlight from reaching
the Moon. During a penumbral
eclipse, the Moon treads through
Earth's penumbra, or pale outer
shadow, where varying amounts of
sunlight dilute the shadow's darkness.
The Moon first touches the penumbra
at 4:53 UT (12:53 a.m. EDT) on
March 25th. Greatest eclipse occurs
at 7:13 UT (3:13 a.m. EDT), when 96%
of the Moon's disk will reside within
Earth's outer shadow. So, so close to
the umbra! Around the time of maximum,
the Moon's southern hemisphere
will appear obviously darkened,
but you should be able to detect
shading well before that, perhaps as
early as 20 minutes into the eclipse.
Watch for the first hint of shadow to
shade the lower left portion of the
Moon. The eclipse ends at 9:33 UT
(5:33 a.m. EDT).
Although the timing of the event
isn't especially favorable for East
Coast and Midwest eclipse-watchers,
farther west the eclipse takes place
at a more reasonable time - starting
at 9:53 p.m. PDT on the evening of
the 24th. Clubs might hold a public
event (everyone likes a full Moon)
with an informal competition to
determine when the first hint of shading
is detectable. Anytime we focus
our attention on a new challenge we
become more discerning observers.
And if you miss this event, you
won't have to wait long for another
chance. On September 18th there will
be a shallow partial eclipse favoring
the eastern half of the U.S. and Canada,
and Central and South America.
sk yand tele scope .o r g * MARCH 2024 49
Moon's
path
U
Ecliptic
M
N
B
E
R
R
P
A
U
A
http://cometchasers.org/home/comet-12p-observations http://cometchasers.org/home/comet-12p-observations http://skyandtelescope.org
Sky & Telescope - March 2024

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