Lunar eclipse: How Earth’s sunset would look from the moon

A
total lunar eclipse or blood moon as seen in a time-lapse series
of images.

Tragoolchitr
Jittasaiyapan/Shutterstock

• The longest total lunar eclipse or blood moon in a
  century will happen overnight on July 27.
• From the moon, Earth will look like it’s surrounded
  by a ring of fire — with its sunset and sunrise connected in a
  loop.
• NASA has an animation showing what
  Earth‘s glowing red ring might look like during a total
  lunar eclipse.
• North America won’t see the eclipse,
  but anyone can watch via a live video webcast.

A total lunar eclipse happens when Earth slips in front of the
sun to cast a ruddy-orange to deep-red shadow on the moon.

This is why the astronomical event is often called
a blood moon. People in Earth’s Eastern Hemisphere can see
the
longest lunar eclipse of the 21st century starting at 19:30
Universal Time (UT) on Friday, July 27.

However, imagine you’re an astronaut who happens to be on the

surface of the moon during a total lunar eclipse, and you
look back home. What would you see?

NASA’s Science Visualization Studio has illustrated the answer to
this question with an animated video.

To someone on the moon during a lunar eclipse, the Earth would
appear to be surrounded by a bright-red ring of fire.

A simulated view of Earth
from the moon during a total lunar eclipse.

NASA’s
Scientific Visualization Studio

The image above is taken from NASA’s animation, which actually
illustrates the precise appearance of Earth and the moon during
the total lunar eclipse that occurred September 27, 2015.

But apart from the position of Earth’s continents, this week’s
lunar eclipse will appear more or less the same from the moon’s
perspective.

Here’s why.

What gives total lunar eclipses an orange-red color

Viewers watch a total solar eclipse.
Reuters

Total lunar eclipses and total
solar eclipses are essentially the reverse of one another.

However, their appearances are very different (whether you’re
observing them from Earth or its natural satellite).

During a total solar eclipse, the moon passes between Earth and
the sun, casting a small, dark shadow on our planet. For those
watching on Earth, the ring of the sun’s light surrounding the
moon looks colorless because the moon has no atmosphere.
(Atmospheres, similar to glass lenses, can refract sunlight.)

Earth is surrounded by a blanket of air, though, and this
lens-like refraction is ultimately why lunar eclipses make the
moon look orange-red.

By volume, about 80% of Earth’s atmosphere is made of nitrogen
gas, or N₂, and most of the rest is oxygen gas, or
O₂. Together, these gases take white sunlight — a mix
of all colors of the spectrum — and scatter around blue and purple
colors. Human eyes are much more sensitive to blues than
purples, which is why the sky looks blue and the
sun yellow to us during daylight hours.

During a sunset or sunrise, sunlight reaching our eyes has passed
through a lot more atmospheric gas, and this effectively filters
out the blues and makes the light appear orange or even red.

A similar thing happens during a lunar eclipse. Earth’s
atmosphere bends and focuses the sun’s light into a glowing,
cone-shaped shadow called the umbra.

A
diagram of the Earth, moon, and sun during a total lunar eclipse
or “blood moon.”
Shayanne Gal/Business
Insider

The red color is never quite the same from one lunar eclipse to
the next due to natural and human activities that affect Earth’s
atmosphere.

“Pollution and dust in the lower atmosphere tends to subdue the
color of the rising or setting sun, whereas fine smoke particles
or tiny aerosols lofted to high altitudes during a major volcanic
eruption can deepen the color to an intense shade of red,”
David Diner, a planetary scientist at
NASA’s Jet Propulsion Laboratory, wrote in a blog post in 2010.

What Earth looks from the moon during a total lunar eclipse

A simulated view of Earth
from the moon just before a total lunar
eclipse.

NASA’s Scientific Visualization
Studio

Roughly 240,000 miles away at the moon, the Earth would look
quite stunning during a lunar eclipse.

“If you were standing on the moon’s surface during a lunar
eclipse, you would see the sun setting and rising behind the
Earth,” Diner wrote. “You’d observe the refracted and scattered
solar rays as they pass through the atmosphere surrounding our
planet.”

On the moon, you’d see the sunrise and sunset of Earth connected
together in a roughly 25,000-mile loop. And on the ground around
you, normally drab-gray lunar dust, or regolith, would look a bit
orange-red.

Earth’s color-tinted umbra is always out there — if you had

enough cash and a spaceship, you could fly into it anytime
you wanted.

However, the moon’s slightly tilted orbit means that it only
passes through our planet’s shadow only about twice every 11 months.

Where and when to see Friday’s total lunar eclipse

The coming eclipse will happen during what’s called a “micro” moon – the opposite of
a super moon. This happens because the moon’s orbit isn’t
perfectly circular, so it appears larger at times and smaller at
others during its roughly 29-day-long orbit around Earth. In this
case, it will look a bit smaller.

North America will be out of luck during the lunar eclipse, since
the moon will be below the horizon. You can still watch the
phenomenon on a live webcast, though.

If the weather cooperates, most of eastern Africa, the Middle
East, and central Asia should see the full and total lunar
eclipse. Scientists in Antarctica should also have a great view.

Europe, eastern Asia, Australia, Indonesia, and other regions
will enjoy a partial lunar eclipse, where the moon passes partly
through Earth’s shadow.

A
map of locations where the total lunar eclipse of July 27 and 28,
2018, will be visible.

Fred
Espenak/NASA Goddard Space Flight Center

The partial eclipse begins when the moon first touches the
penumbra, or outer shadow, of Earth. According to NASA, that should happen at
17:14 Universal Time on July 27.

The total eclipse — when the moon is fully inside the red-hued
umbra of Earth — starts at 19:30 UT and ends at 21:13 UT. That’s
a full 1 hour 43 minutes, which is just four minutes shy of the
longest total lunar eclipse possible, according to
EarthSky.

The partial eclipse will resume immediately afterward, as the
moon starts to leave Earth’s shadow. The whole event will be over
at 23:28 UT (which might technically be early on July 28,
depending on where you live).

See NASA’s animation below of a total lunar eclipse from the
moon.