- The longest total lunar eclipse or blood moon in a century will happen in the early hours of July 28.
- 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.
- Only those in Western Australia will be able to see the entire 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.
It will begin about 3.15am (AEST) Saturday, July 28. The Moon will start to turn red from about 5.30am.
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 Visualisation 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.
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.
What gives total lunar eclipses an orange-red colour
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 colours of the spectrum – and scatter around blue and purple colours. 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.
The red colour 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 colour 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 colour 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
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-grey lunar dust, or regolith, would look a bit orange-red.
Earth’s colour-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.
Here’s when to catch it in Australia (times in AEST)
3.15am: The penumbral eclipse begins when the Earth’s penumbra starts to touch the moon
5.30am: The total eclipse can be seen when the moon is fully red
6.21am: Maximum eclipse
7.13am: Total eclipse ends and moon will set in the west-southwest
See NASA’s animation below of a total lunar eclipse from the moon.
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