Artist’s representation of a total solar eclipse, with a new moon in the foreground and the Sun’s corona visible in the background. Download the Poster NASA/Vi Nguyen
On April 8, 2024, much of North
America will experience a solar eclipse: a cosmic alignment of Sun, Moon, and Earth, in that order. The Moon’s
shadow path will make landfall on Mexico’s Pacific coast, cross the United
States from Texas to Maine, and exit North America via Newfoundland, Canada,
continuing into the Atlantic Ocean.
Learn how to safely observe the 2024 Solar Eclipse
It's All About Perspective
Solar eclipses on Earth are a
convenient coincidence. The Sun’s diameter is about 400 times larger than the
Moon’s, and the Sun is almost 400 times farther away from us than the Moon is.
This combination makes the Sun and Moon appear nearly the same size in our sky,
setting up a spectacular show when they align. Try experimenting with apparent
size for yourself by holding up a small item, like your thumb, and moving it
closer and farther away to block different-sized objects from your view.
The Moon’s distance from Earth
varies, though only slightly. The Moon’s orbit is not a perfect circle, and it
is not quite centered on our planet. At its closest, the Moon is about
twenty-eight Earth diameters away; at its farthest, about thirty-two. As a
result, the Moon’s apparent size changes over time, and eclipses are not all alike.
A total solar eclipse is only
possible when the Moon is closer to Earth than average. When the Moon is
farther away, its apparent size is smaller than the Sun’s, so it does not
completely block the Sun’s bright disk. In this configuration, when the Moon passes
between Earth and the Sun, a “ring of fire” remains visible – that’s an annular
solar eclipse.
An Orbital Dance
Video tutorial describing the 2024 total solar eclipse
and explaining the Moon's role in creating it. Credit: NASA's Goddard Space
Flight Center
Ever wonder why solar eclipses
don’t happen more often? Earth, Moon, and Sun don’t line up perfectly every
month because the Moon’s orbit is tilted by about 5 degrees compared to Earth’s
orbit around the Sun. Most of the time, the Moon’s shadow misses our planet.
When all three celestial bodies do
align, views of the eclipse depend not just on our position in the solar
system, but also on our location on Earth. The Moon’s shadow has two parts, the umbra and the
penumbra. Observers in the umbra (or “path of totality”) will experience a
total solar eclipse. For those in the penumbra, the eclipse will be partial.
2024 Total Solar Eclipse shadow path map, built using datasets from several NASA missions. For more information, visit NASA’s Scientific Visualization Studio: The 2024 Total Solar Eclipse. NASA's Scientific Visualization Studio
If you are planning to observe the
eclipse, you’ve probably consulted a shadow path map like this one. But how do
we know exactly where and when the Moon will cast its shadow? Eclipse
prediction depends, first and foremost, on understanding the positions and
movements of the Moon, Sun, and Earth. Modern maps build on a long human
history of eclipse forecasting. And since 2009, NASA’s Lunar Reconnaissance
Orbiter (LRO) has been mapping the Moon in unprecedented detail. LRO’s lunar
topography data enables us to make more accurate eclipse predictions than ever
before.
Moonshadow: The Making of a Map
The Moon is a rugged world of
peaks, craters, basins, and valleys. Since the lunar horizon is bumpy and
jagged, the shadow it casts is not quite round. Knowing the precise shape of the Moon helps us understand exactly where
its shadow will darken Earth’s surface. Of course, our own planet is not
perfectly round, either. Today’s eclipse maps account not only for the lunar landscape, but also for the contours
of Earth’s mountain ranges, lowlands, and other features.
Uneven lunar terrain partially blocks the Sun in this composite image of a partial solar eclipse, showing the Moon (visualization based on Lunar Reconnaissance Orbiter data) passing between Earth and the Sun (as imaged from space by the Solar Dynamics Observatory spacecraft on October 7, 2010). NASA’s Scientific Visualization Studio
Bursts of Light: Baily's Beads and the Diamond Ring Effect
Casual observers don’t usually
notice that the Moon’s silhouette is rough around the edges. At a distance of
239,000 miles (that’s the average gap between Earth and the Moon), our nearest
neighbor in space looks round – even mountains appear too small for the human
eye to distinguish. But, for two brief moments during a solar eclipse, craggy
lunar terrain commands the spotlight.
On the brink of totality, as the
Moon moves into full Sun-blocking position, the Sun’s edge doesn’t go dark all
at once. Last rays of sunlight peek through valleys on the lunar horizon. These
isolated areas of intense brightness can resemble a string of glowing beads or
a single dramatic burst of light like the gem on a ring. The same phenomena,
sometimes called Baily’s Beads and the Diamond Ring Effect, can also occur as
the Moon edges out of totality (or annularity). Since we know the shape and
position of the Moon so well, we can predict where the first and last bits of
sunlight will appear.
Baily’s Beads as seen during the August 21, 2017 total solar eclipse. NASA/Aubrey Gemignani
NASA Eclipse Science and You
NASA scientists take full advantage
of the unusual
atmospheric and environmental conditions the Moon’s passing shadow creates, and you can
too. Here are just
a few places to start.
- Join a community eclipse
science project like Eclipse Soundscapes or GLOBE Eclipse.
- A solar eclipse is a rare
opportunity to directly observe a new
moon. Document your experience
and kick off a month of Moon observations with our special edition Moon Observation Journal.
- Learn more about lunar
and solar eclipses.
- Connect with observers
around the world and keep celebrating the Moon’s place in science and
culture on the next International
Observe the Moon Night, Sept.
14, 2024.
Science Advisor: Ernie Wright, NASA's Goddard Space Flight Center
Source: Total Solar Eclipse 2024: The Moon’s Moment in the Sun (nasa.gov)
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