Are There Solar Eclipses on the Moon
A solar eclipse on Earth
There's a solar eclipse on Earth if the Moon is in its new moon phase and properly lined up with the Earth and the Sun. Before we go to the Moon, let's just consider what such a solar eclipse would look like.
(1) The Moon's shadow moves across the Earth. If we're in one of those lucky places where the inner dark part of the shadow falls – the umbra – we could see a total eclipse.
(2) The Moon is small, so the whole eclipse takes around two hours, with totality usually lasting just a few minutes. In addition, from Earth the Sun and the Moon appear to be the same size, so there's a snug fit at totality.
(3) As the dark Moon moves in front of the Sun, we would see it silhouetted against the Sun's disk. At the beginning and end of totality, the diamond ring effect appears. The Moon has mountains and valleys, so the edge of its disk isn't perfectly smooth. When sunlight bursts through a gap in the Moon's irregular landscape it looks rather like a diamond ring. This animated GIF by Pedro Ré shows the diamond ring effect and the solar corona.
(4) The corona, the Sun's outer atmosphere, is visible only when the Sun is totally eclipsed. Normally, the Sun's bright photosphere layer washes out our sight of the tenuous corona.
(5) Stars and other celestial objects don't go away during the day, but they usually can't compete with the Sun. However they do appear during a total eclipse.
The view from space
Looking from the Moon at a solar eclipse on Earth, all that would be visible is the Moon's shadow on Earth. Closer to home, astronauts have also seen this. French astronaut Jean-Pierre Haigneré was on the Mir space station over Europe when he took this picture of Earth during the solar eclipse of August 11, 1999.
A solar eclipse on the Moon
Now let's be off to the Moon.
The Moon is in its full moon phase and properly aligned with the Earth and the Sun. That means that while we on the Moon enjoy a solar eclipse, many people on Earth will be seeing a lunar eclipse.
The Earth is bigger than the Moon, so our eclipse is going to be longer than a solar eclipse on Earth. Overall it could be over five hours, and totality would also last much longer than it does on Earth. The Moon and the Sun may appear to be the same size from Earth, but from the Moon Earth seems to be over three times bigger than the Sun.
Cities faintly light the Earth's night side. Therefore we'll see the Sun and a faintly glowing supersize Earth very slowly approaching each other. And when Earth is in front of the Sun we won't miss out on the "diamond rings" that bracket totality. The Japanese Kaguya Moon probe imaged a solar eclipse on the Moon in 2009. (The ring seems to be incomplete because the limb of the Moon was obscuring the view.) [Credit: JAXA/NHK]
But you might be surprised to see a glowing red ring around the Earth when it blocks the Sun. It can't be an annular eclipse, because Earth is too big for that. An annular eclipse happens when the Moon is too far away to cover the Sun completely.
But Earth has something the Moon doesn't – an atmosphere. No sunlight can get through the body of the planet, but that's not true of the atmosphere. Sunlight is scattered and bent as it travels through the atmosphere, creating the reddish glow of a sunset. Our friends watching the lunar eclipse on Earth will also see the Moon go a reddish color at totality when the only light reaching it is this glow.
Here's a painting by French astronomer and artist Lucien Rudaux, painted in the 1930s. It suggests what a solar eclipse would look like on the Moon. He shows the Moon bathed in an eerie red light, but also shows a very prominent corona. We'll see the red glow, but our view of the corona will be noticeably reduced by the Earth covering so much of the Sun.
What a splendid sight! If ever there are tourist trips to the Moon, solar eclipses will surely be much in demand by extraplanetary travelers.
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