The longest total lunar eclipse of the 21st century is just a
month away.
The total
phase of the "blood moon" eclipse of
July 27 will last 1 hour and 43 minutes, during which Earth's natural satellite
will turn a spectacular red or ruddy-brown color. From start to finish, the
entire celestial event will last nearly 4 hours.
Source: space.com
The eclipse won't be visible to viewers in North America, except
via webcasts. But observers in much of Africa, the Middle East, southern Asia
and the Indian Ocean region will get an eyeful, given cooperative weather,
according to lunar scientist Noah Petro, of NASA's Goddard Space Flight Center
in Greenbelt, Maryland.
Unlike
with solar eclipses, you need
no special equipment to observe lunar eclipses. These latter events, which
occur when the moon passes into Earth's shadow, are safe to view directly with
the naked eye, telescopes or binoculars.
The moon turns deep red or reddish brown during eclipses,
instead of going completely dark. That's because some of the sunlight going
through Earth's atmosphere is bent around the edge of our planet and falls onto
the moon's surface. Earth's air also scatters more shorter-wavelength light (in
colors such as green or blue); what's left is the longer-wavelength, redder end
of the spectrum.
Where and when will it be visible?
The timing if this total lunar eclipse means
it won't be visible from North America, though much of the Eastern Hemisphere
of Earth will see part or all of the eclipse. The entire eclipse will be
visible from Africa, the Middle East and countries in central Asia. The eclipse
will be visible from eastern South America as it is ending, and from Australia
as it is beginning.
The time of greatest eclipse will be 4:21 p.m. EDT (2021 GMT) on July 27, according to EarthSky.org. The total eclipse will last
from 3:30 p.m. to 5:13 p.m. EDT (1930 to 2113 GMT). There will also be some time before and
after when the moon is in the lighter part of Earth's shadow, which is called
the penumbra. Including that penumbral time, the eclipse will last for 3 hours
and 55 minutes.
"What controls the duration of the lunar eclipse is the position
of the moon as it passes through the Earth's shadow," Petro told
Space.com. The darkest part of Earth's shadow is called the umbra. You can
picture the umbra as a cone extending from Earth in the opposite direction to
the sun, Petro explained.
"The moon can either graze through the cone, or go right
through the middle. That [the middle] gets a longer-duration eclipse," he
said. "This time, the moon is passing closer to the center of that cone,
and it's therefore a little bit longer than the eclipse we had back in
January."
Additionally, the moon will be at a farther point from Earth
along its orbit, EarthSky pointed out. That means the moon will appear slightly
smaller in the sky and will take a little bit longer to go through Earth's
shadow.
Petro
is also the project scientist for NASA's Lunar Reconnaissance Orbiter(LRO),
which has been orbiting the moon for nine years. It is best-known for obtaining
detailed information on water ice and taking high-resolution pictures of
spacecraft on the lunar surface. Because LRO is an older probe, most of its
components (except for battery warmers and the like) will be turned off during
the eclipse, to preserve the solar-powered spacecraft's battery and keep it
safe during the greatest part of the eclipse, Petro said.
When is the
next lunar eclipse?
The next
total lunar eclipse visible from North America will occur on Jan. 21, 2019.
Totality on that day will last 1 hour and 2 minutes, and the eclipse will
especially favor viewers on the West Coast. That year will also see a partial
eclipse, on July 16, 2019 — the 50th anniversary of the launch of the first
moon landing mission, Apollo 11. LRO will likely
still be operating then, having passed its 10th anniversary of arriving at the
moon on June 23, 2019.
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