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Is it possible to block the surrounding light in a solar eclipse if we made the moon bigger or closer to the earth? In an eclipse, you always see a ring of light surrounding the moon, but I am wondering if it's possible to completely block any light so you only see a dark circle in the sky. How much bigger does the moon have to be in order to achieve that?

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    $\begingroup$ Just take a photo during totality, not seconds before or after. $\endgroup$
    – JohnHoltz
    Apr 10, 2022 at 14:59
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    $\begingroup$ It's not possible to make the moon bigger or closer to Earth... $\endgroup$
    – James K
    Apr 10, 2022 at 17:06
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    $\begingroup$ @James K Furthermore, there is no law of science making it it impossible to enlarge the Moon, it would merely be a very, very, very, very, big megaproject as I explain in my answer. For example, if the Moon was terraformed to have a breathable atmosphere a roof would ahave to be built all over the Moon to hold the air in, thus increasing the diameter of the Moon at least slightly. $\endgroup$ Apr 10, 2022 at 21:04
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    $\begingroup$ There seems to be a lot of ultra-concrete responses here. Let's just answer with a simple example: if you're in the ISS, the Earth provides a complete eclipse, including the sun's corona. $\endgroup$ Apr 11, 2022 at 11:32
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    $\begingroup$ Totally unrelated to the question itself - that picture keeps making me squint at it, even though I know it's just on my monitor. $\endgroup$
    – Bobson
    Apr 11, 2022 at 19:30

2 Answers 2


Let's clarify what "ring of light" you want to cover. In the original photo, the bright spot is the photosphere ("P" in the annotated copy or the original image). The photosphere is the bright disk you see when the Sun is not in an eclipse. This photo was taken seconds before or after totality, so the a small fraction of the photosphere was still visible. The complete photosphere would have been covered a few seconds earlier or later, and the "Sun" would not be visible. Photosphere (P) visible at second or third contact

Slightly visible in the original photo is the inner corona. The corona is the outer atmosphere of the Sun that is only visible during an eclipse. During totality, the corona extends out much further than "a ring". As seen in this photo (2017 Aug 21), the corona extends out at least 5 times the diameter of the Moon. Corona visible during total solar eclipse

Whether you want to make the apparent diameter of Moon 5% larger (to cover the inner corona) or 400% larger, the technology do either one is not realistic.

A cheaper alternative using existing technology is to ride in a spacecraft to be closer to the Moon. You can choose how much of the Sun you want to be blocked.

Incidentally, millions of people see the Sun completely covered every day. It's called night.


Part One:

Eclipses of the Sun by the Moon come in four types:

A total eclipse occurs when the dark silhouette of the Moon completely obscures the intensely bright light of the Sun, allowing the much fainter solar corona to be visible. During any one eclipse, totality occurs at best only in a narrow track on the surface of Earth.[6] This narrow track is called the path of totality.[7]

An annular eclipse occurs when the Sun and Moon are exactly in line with the Earth, but the apparent size of the Moon is smaller than that of the Sun. Hence the Sun appears as a very bright ring, or annulus, surrounding the dark disk of the Moon.[8]

A hybrid eclipse (also called annular/total eclipse) shifts between a total and annular eclipse. At certain points on the surface of Earth, it appears as a total eclipse, whereas at other points it appears as annular. Hybrid eclipses are comparatively rare.[8]

A partial eclipse occurs when the Sun and Moon are not exactly in line with the Earth and the Moon only partially obscures the Sun. This phenomenon can usually be seen from a large part of the Earth outside of the track of an annular or total eclipse. However, some eclipses can be seen only as a partial eclipse, because the umbra passes above the Earth's polar regions and never intersects the Earth's surface.[8] Partial eclipses are virtually unnoticeable in terms of the Sun's brightness, as it takes well over 90% coverage to notice any darkening at all. Even at 99%, it would be no darker than civil twilight.[9] Of course, partial eclipses (and partial stages of other eclipses) can be observed if one is viewing the Sun through a darkening filter (which should always be used for safety).


The orbit of the Earth around the Sun is elliptical, making Earth sometimes closer to and sometimes farther from the Sun. Since the physical diameter of the Sun, doesn't change, that means that the apparant or angular diameter of the Sun as seen from Earth changes.

The orbit of the Moon around the Earth is elliptical, making the Moon sometimes closer to and sometimes farther from the Earth. Since the physical diameter of the Moon, doesn't change, that means that the apparant or angular diameter of the Moon as seen from Earth changes.

So when the center of the Moon passes betweent the Earth and the center of the Sun, the angular diameter of the Moon can be larger than that of the Sun, and there can be a total eclipse, or the angular diameter of the Moon can be less than that of the Sun, and there can be an annular eclipse.

During annular eclipses, the photosphere of the Sun is not totally covered and appears as a thin bright ring around the Moon. During total eclipses, the photosphere is completely covered and hidden by the Moon. But the darkening of the Sun's light during total eclipses allows the dim corona, or inner atmosphere of the Sun, to be visible, usually extending a few times the angular diameter of the moon and looking rather irregular.

Part Two;

There are two interpretations of the question.

One) Can humans enlarge the moon and/or bring it closer to the Earth?

Two) Could a possible habitable world similar to Earth have a moon Larger than Earth's Moon or closer to the planet than the Moon is to Earth.

Part Three: Making the Moon bigger and/or closer.

Both would be very, very, very, very, very, very big projects which might take many thousands or millions of years. But enlarging the Moon would seem to be many thousands of times easier, though still very, very, very difficult.

For example, it would obviously be possible to take inflatable buildings to the Moon's surface and inflate them with some sort of gases. And if enough huge inflatable buildings are taken to the Moon, it is possible to cover the entire surface of the Moon with inflated buildings and so increase it's diamater somewhat. And if a very vast giant project is made, perhaps the Moon's diamter might be increased by thousands of miles.

Such a project would be a form of a shellworld, and there are other theoretical forms of shellworld mega projects:

A shellworld1[3] is any of several types of hypothetical megastructures:

A planet or a planetoid turned into series of concentric matryoshka doll-like layers supported by massive pillars. A shellworld of this type features prominently in Ian M. Banks' novel Matter.

A megastructure consisting of multiple layers of shells suspended above each other by orbital rings supported by hypothetical mass stream technology. This type of shellworld can be theoretically suspended above any type of stellar body, including planets, gas giants, stars and black holes. The most massive type of shellworld could be built around supermassive black holes at the center of galaxies.

An inflated canopy holding high pressure air around an otherwise airless world to create a breathable atmosphere.[4] The pressure of the contained air supports the weight of the shell.

Completely hollow shell worlds can also be created on a planetary or larger scale by contained gas alone, also called bubbleworlds or gravitational balloons, as long as the outward pressure from the contained gas balances the gravitational contraction of the entire structure, resulting in no net force on the shell. The scale is limited only by the mass of gas enclosed; the shell can be made of any mundane material. The shell can have an additional atmosphere on the outside.[5][6]


So it would be possible to enlarge the Moon using less effort than merely dumping counless gazillions of tons of rock on it.

But it would still be a very vast mega project. And even enlarging the Moon by dumping gazillions of tons of space rock on it would be a much smaller mega project than trying to move the Moon closer to Earth.

Part Four: A Hypothetical Earth like planet with a moon that was larger and/or closer than Earth's Moon.

It is certainly possible for an Earth like planet to have no moon, like Mercury or Venus, or to have one moon like Earth, or to have two moons like Mars, or to have more than two moons. Pluto, a dwarf planet, has five known moons. And possibly some Earth like planets can have more than five moons.

There are some theories that having a large moon is important to make an Earth like planet habitable. If those theories are correct - and it is not know if they are correct - then each habitable planet is likely to have one large moon in addition to possible smaller moons.

The Moon is more massive, relative to the mass of the Earth, than any known moon of any other planet in our solar system. However, Charon, the largest moon of the dwarf planet Pluto, is much larger and more massive compared to Pluto than the Moon is compared to the Earth. And it is speculated that the moons of Pluto, including the massive Charon and the four small moons, were formed by a gigantic collison between astronomical objects, similar to how the Earth's Moon is believed to have been formed.

So as far as we know now, it is certainly possible for an Earth-like habitable planet to no moon, or a moon much smaller than the Moon, or a moon the same size as the Moon, or a moon much larger than the Moon.

Can the hypothetical large moon of a hypothetical habitable Earth like planet orbit the planet much closer than the Moon orbits Earth?

Yes. Astronomers studying the orbit of the moon calculated that tidal effects would slow down the rotations of the Earth and the Moon and cause the Moon to slowly spiral outward from the Earth.

Some of the Apollo missions left reflectors on the Moon pointed at the Earth. Astronomers point intense lasers at the Moon, and detect very faint reflections from the reflectors on the Moon. By detecting the time it takes for the reflections to be detected, they can measure the distance to the Moon and calculate how slowly the Moon is receeding from the Earth.

The Moon is receeding at a rate of about 38.30 plus or minus 0.08 millimeters per year. So in 500 million years the Moon should have receeded 1.915 times 10 to the 10th power millimiters or 19,150,000 meters, or 19,150 kilometers.

And photosynthic lifeforms created an oxygen rich atmosphere on Earth, making Earth habitable for humans and other lifeforms which need to breathe oxygen, over 500 million years ago. So it is possible that when Earth first became habitible for beings like humans, the Moon might have been close enough to always cover the entire photosphere of the Sun during central eclipses, though it would not have been close enough to cover the entire solar corona.

Of course the farther the Moon gets from Earth, the weaker the tidal interactions are, and so the slower the Moon moves away from Earth. Thus the Moon must have actually been much more than 19,500 kilometers closer to Earth 500 million years ago.

The tidal interactions between the Moon and the Earth slow down their rotation rates. The rotation period of the Moon has slowed down until it equals the period of the Moon's orbit around the Earth, making the Moon tidally locked to the Earth.

Because the tidal effect of the Moon on the Earth is weaker than the Earth's effect on the Moon, the rotation of the Earth has not been slowed as much. But it has been slowed enough to make the Earth's day several times as long as it originally was, and the Earth's rotation is still slowing. It has been calculated that if the Earth's rotation slows enough for it to be tidally locked to the Moon, the Moon would cease to move away from the Earth and the distance between would remain unchanged.

And if a much larger moon formed close to an Earthlike planet, its much stronger tidal forces would slow the rotation of the Earthlike planet much faster than the Moon slowed the rotation of the Earth. Thus the two worlds might both become tidally locked while the moon was still close enough to the planet to totally cover the star's photosphere, and maybe also its corona, during total stellar eclipses.

I note that not only is Charon tidally locked to Pluto, but Pluto is also tidally locked to Charon, which means that tidal forces no longer drive Charon outward from pluto.

So it an Earth like planet formed a much larger moon close to it, that moon might cease spiralling outward from the planet, while it still had an angular diameter wide enough to cover their star's photosphere and even the star's corona.


I don't know if you were asking about the possibility of a super gigantic future project to inclrease the angular diameter of the Moon as seen from Earth, or about the possbiility of a hypothetical habitable planet with a moon having an anglar diameter large enought to cover their star's photospere and maybe even its corona.

So I answered both.

And if you intended to ask the second question for a story you are thinking about writing you should ask a question about it on the Worldbuilding stack Exchange.


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