NASA Space
Science News
Holiday revelers
who happen to find solar filters under their Christmas tree this
year can put the unusual gift to immediate use. That's because
a solar eclipse is coming on Christmas Day, 2000. Across parts
of North America, the winter landscape will briefly assume an
eerie cast, and cooler-than-usual winds might swirl as the New
Moon glides across the face of the Yuletide Sun.
But don't
expect the lights to go out completely. This eclipse will be a
partial one -- at most 72% of the Sun's diameter will be occulted
by the Moon.
Above: Photographer Thomas Colin captured this dramatic sunrise
on August 11, 1999, when the partially eclipsed Sun appeared above
a cloudy Quebec horizon.
Sky watchers
who live in the continental United States, Canada, Mexico, or
the Caribbean can enjoy the show, but only if they're careful.
Looking directly at the Sun this Christmas can inflict blindness
just as surely as it would on any other day. A partially-eclipsed
Sun is still very bright.
"Extreme
care must be taken when watching the eclipse," writes Fred
Espenak of the Goddard Space Flight Center. "Never look at
the Sun with the naked eye or through any optical device such
as [unfiltered] telescopes or binoculars. Human curiosity impels
some people to stare directly at the Sun during an eclipse and
this can cause permanent damage to your eyesight."
Fortunately,
there are safe ways to view an eclipse. Chief among them is projecting
an image of the Sun onto a screen through a properly shielded
telescope or a properly shielded pair of binoculars. Sky &
Telescope's web page "How
to Watch a Partial Solar Eclipse Safely" explains such
techniques.
Above: In this diagram from Sky & Telescope (copyright
2000, all rights reserved) little crescents show how the Sun will
look at mid-eclipse in various North American cities on Christmas
Day. Click on image for larger view, which will also show the
local times of maximum eclipse.
Residents
of the Pacific northwest and western Canada will have to dash
outside just after sunrise for best viewing. The eclipse will
already be in progress as the Sun peaks above the eastern horizon
-- a potentially dramatic sight.
Drowsy sky
watchers east of the Rocky Mountains can sleep a bit longer, provided
their kids will allow it on Christmas Day. The maximum eclipse
over Denver won't happen until nearly 10 a.m. local time, while
people on the Atlantic coast can wait until after lunch to see
the show. Fred Espenak has tabulated eclipse viewing times for
cities in the United States, Canada, and Latin America.
 Right:
This unique eclipse animation, courtesy of Dr. Andrew Sinclair,
shows the motion of the Moon's shadow across Earth's surface during
the Dec. 25th eclipse.
The biggest
"dent" in the Sun will appear at 1723 Universal Time
(12:23 EST) on Dec. 25th when 72% of the Sun's diameter will be
covered by the Moon. Unfortunately, only the residents of Baffin
Island in northern Canada will see so much of the Sun obscured.
Elsewhere, the eclipse magnitude will vary from ~60% in the northeastern
USA to less than 20% in the far southwest. (Eclipse magnitude
is the percent of the Sun's diameter covered by the Moon.)
Observers
in those northeastern regions where the eclipse magnitude will
be greatest might note a subtle change in the cast of sunlight
across the landscape. Elsewhere, the day will appear as brightly
lit as usual.
And if you
happen to spend a little too long opening gifts on Christmas morning,
and miss the eclipse, don't despair! There are at least two solar
eclipses every year and --on rare occasions-- as many as five.
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