Sky & Telescope - October 2023 - 40

Eclipse Preview
uBEFORE AND AFTER The moments
immediately before (top) and after annularity
(bottom) as recorded during the solar
eclipse of October 3, 2005. During a total
eclipse, the new Moon passes directly in
front of the Sun. An annular eclipse occurs
when the disk of the Moon is too small to
completely cover the face of the Sun.
when they meet the Gulf Coast,
leaving a band of cloud across
the shadow path that can later
redevelop into a larger disturbance.
Thunderstorms, sometimes
with severe weather, can form
overnight along the coast and
persist past eclipse time, throwing
up large and dense cloud shields.
However, 23 years of satellite
images show that sunny spots
existed within 50 miles of San
Antonio on two-thirds of the past
October 14ths. The challenge is to
find the gaps in the cloud cover at
short notice.
Mexico and South
The antumbral shadow takes 25
minutes to cross 1,000 km of
open water in the Caribbean before it encounters the west
coast of the Yucatán Peninsula at 13:23 EST. The eclipse
track crosses parts of three countries in the Yucatán: Mexico,
Guatemala, and Belize. Belize City (population 60,000)
is near the central line and experiences an annular phase
lasting 5m 11s.
In the Yucatán cloudy days are the rule according to
satellite data. But here again, the type of cloud makes all the
difference - they're mostly small cumulus clouds that will
likely dissipate with the approaching eclipse. Because of cool
waters offshore, locations near the coast have a more promising
climatology than those inland. That's why residents of
Campeche, Mexico, would have been able to view an eclipse
on about 80% of the past 23 October 14ths. This October,
the eclipse is high in the sky over the Yucatán, and the bright
solar ring should be relatively easy to follow in a thin overcast.
The track next crosses Honduras and Nicaragua before
slipping back into the Caribbean. The instant of greatest
eclipse, when the axis of the Moon's shadow passes closest
to Earth's center, occurs in the Caribbean at 12:59:29 EDT
(17:59:29 UT). The duration is 5m 17s, the path width is 184
km, and the obscuration (the fractional area of the Sun's disk
covered by the Moon) is 0.905. The ground speed has slowed
down to a relatively leisurely 2,200 km/h.
After traversing western Panama, the eclipse track enters
Colombia as it gradually curves east toward Brazil - the
final country within the path. As the shadow reaches Brazil's
40 OCTOBER 2023 * SKY & TELESCOPE
Atlantic Coast, Natal (population
890,000) residents witness a 3m
35s annular phase in the late afternoon
(16:46 Brasilia Time), with
the Sun just 6° above the horizon.
Four minutes later (at 19:50 UT),
the antumbra leaves Earth and the
annular eclipse ends.
Throughout this part of the
annular eclipse track, clouds are
primarily convective, blossoming
with large storms that combine
to bring an average cloudiness
approaching 100%. However, there
are small oases in this gloom,
especially in eastern Brazil, where
average cloud cover drops to 30%,
making this small part of the
track one of the most promising
for viewing the event.
Some Final Notes
Over the course of 3 hours and
34 minutes, the Moon's antumbral
shadow traverses 13,800
kilometers and covers 0.57% of
Earth's surface area. The American
Southwest is easily one of the most
scenic areas in the U.S. The cooler, post-summer temperatures,
coupled with frequently clear skies, make the area
particularly attractive for both tourists and eclipse chasers
alike. And amateur astronomers will also revel in the incredibly
dark night skies the region has to offer.
Even if you don't travel to the path of annularity, most
viewers will see an intriguing partial eclipse. Looking up
from Miami, Florida, at mid-eclipse (using safe viewing
techniques, of course), you'll see 67% of the solar disk covered
by the Moon. From Los Angeles, California, it will be
78%. The partially eclipsed Sun will be worth viewing even
from such widely separated locations as Vancouver, British
Columbia (82%), Minneapolis, Minnesota (57%), and New
York City (35%).
You may see this annular eclipse as just the opening act
to totality in 2024, but the appearance of a perfectly symmetric
annular ring is wonderfully beautiful in its own way.
The annular eclipse also offers an excellent opportunity to
witness Baily's Beads - glimmers of sunlight shining through
deep lunar valleys. After all, Francis Baily first described this
phenomenon while observing an annular eclipse in 1836.
¢ FRED ESPENAK, a.k.a. Mr. Eclipse, is world-renowned for
his eclipse predictions and photography. JAY ANDERSON is
a Canadian meteorologist who has been dispensing advice
to eclipse chasers since 1979. His forecasts can be found at
eclipsophile.com.
FRED ESPENAK
http://www.eclipsophile.com
Sky & Telescope - October 2023

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