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I just got to see a solar eclipse today, not total but 86% eclipsed. And hopefully I will see a total solar eclipse in Toledo, OH in 7 years.

But this eclipse inspired me to ask this question.

I know that for a planet with multiple moons, it is absolutely possible that a solar eclipse and a lunar eclipse could occur at the same time. I also know that here on Earth, sometimes the moon is visible in daylight, either early morning or late afternoon depending on whether it is before or after a full moon. I myself have seen the moon during the day.

Now, I know that the only solar eclipse during which a lunar eclipse would likely be visible is a total solar eclipse because during a total solar eclipse, it goes dark and all the wildlife think it is night when it is just an eclipse.

So if a planet has 2 or more moons that are in resonance for stability reasons, could it be that a moon that is close enough to block the star or star system does block the star or star system while another moon further away gets fully eclipsed by the planet and thus you have a total solar eclipse visible on 1 side of the sky and a total lunar eclipse visible on the other side of the sky from the same area(like about the size of an average city)?

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  • $\begingroup$ "I know that the only solar eclipse during which a lunar eclipse would likely be visible is a total solar eclipse", actuall most solar eclipses are accompanied by a lunar eclipse, but it must be two weeks prior to or afterwards because the moon needs to be on the opposite side of the planet. $\endgroup$
    – Octopus
    Aug 21, 2017 at 19:36
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    $\begingroup$ Sure, they could be visible simultaneously (from two separate mooons) but you would have to be on the limb of the planet, ie. see to the day side and the night side at the same time. Both would be low in the sky, close to the horizon in opposite directions. $\endgroup$
    – Octopus
    Aug 21, 2017 at 19:39
  • $\begingroup$ To explain Octopuses's comment: A moon eclipse is produced by the shadow of the planet. The shadow of the planet is, obviously, exactly opposite the sun. So when a moon is eclipsed it must be at the antisolar point -- exacly opposite the sun. To see both a sun eclipse and a moon eclipse at the same time you must be exactly on the line dividing night from day; the eclipsed moon and the sun would then be on opposite points on the horizon. $\endgroup$
    – AlexP
    Aug 21, 2017 at 19:43
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    $\begingroup$ Not at the poles. The poles are seldom on the terminator line; as in, if the planet has a non-zero axial tilt, the poles are on the terminator line only twice per year at equinoxes. And yes, eclipses are visible only from a well defined path (much narrower for solar eclipses than for lunar eclipses). $\endgroup$
    – AlexP
    Aug 21, 2017 at 19:58
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    $\begingroup$ Another way to "bend the rules" would be to have a planet with multiple moons in a binary sun system have an eclipse both both suns at the same time. $\endgroup$
    – ohwilleke
    Aug 22, 2017 at 17:13

2 Answers 2

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No.

If You see the "sun" (however eclipsed) you cannot see the cone of shadow projected by the planet where you stand (it's below the horizon), so you cannot see the eclipsed moon and vice versa.

You could see both eclipses from a third body, but then the body from where you see the solar eclipse is not the same eclipsing the second moon. You need four bodies (plus the star).

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    $\begingroup$ Not true. There was one day a few years ago in my town where, in the wee hours of the morning, you could see the rising sun, the setting moon, and a simultaneous lunar eclipse. $\endgroup$
    – Octopus
    Aug 21, 2017 at 20:20
  • $\begingroup$ @Octopus: I've never heard of such a thing, and frankly it goes against everything I know about eclipses. Can you fill in some details? When & where did you see this? (The exact location & date would be great, but if you're not comfortable providing these or can't remember them, as much detail as you can provide would be helpful.) $\endgroup$
    – Michael Seifert
    Aug 21, 2017 at 20:28
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    $\begingroup$ @Michael, It's called a selenehelion. Heres one article. $\endgroup$
    – Octopus
    Aug 21, 2017 at 20:32
  • $\begingroup$ @Octopus: Thanks! Atmospheric refraction always seems like a bit of a cheat to me, but it's interesting to know that the effect can be large enough for this to happen. $\endgroup$
    – Michael Seifert
    Aug 21, 2017 at 20:53
  • $\begingroup$ @Octopus - you should expand that into an answer! $\endgroup$
    – Drgabble
    Aug 23, 2017 at 16:59
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Yes and No

In order to see a lunar eclipse on Earth while still seeing the Sun, you need to be in a place with "perfect" atmospheric variable, as such that light refraction brings the image of the moon above the horizon during day time. Most of the time you will never see both the sun and the eclipsed moon at the same time and it's just a very VERY rare phenomenon and is only seen in specific places. This phenomenon by the way is called a "selenelion" so I will use that term.

Of course a planet with multiple moons can have both a solar and lunar eclipse happening at the same time. However to see a selenelion on such planet, not only should you hope for atmospheric refraction to bring the image of the eclipsed moon above the horizon but the shadow of the moon eclipsing the sun must be over the terminator (which happens when an eclipse starts or ends). Usually when it begins or when it ends, a solar eclipse lasts much shorter than when the shadow is over land that is or is almost directly under the sun.

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