3 ms·

Besides the refraction, there's also a geometrical effect. An observer is not on the line of the Sun-Earth-Moon centers; he's offset from it by Earth's radius

Besides the refraction, there's also a geometrical effect. An observer is not on the line of the Sun-Earth-Moon centers; he's offset from it by Earth's radius at Earth's surface, so he's at one point of a triangle and sees a Sun-Moon angle of slightly less than 180º. The refraction is a larger effect, but even an airless planet could have an observer seeing the centers of both the Sun and Moon at eclipse time just above the horizon.

tobr 4y ago
That is interesting… but to my intuition, it seems like that would have the opposite effect? You are offset in the “wrong” direction, ie the sun and the moon are further “down” and more obscured by the earth? I might be thinking all wrong about this, though. I’d also question if this can have any meaningful effect on the sun, which is about 23500 Earth radii away. That’s a very, very slight perspective shift.
- zamadatix 4y ago
  Imagine an ant standing on some random point on a soccer ball in the middle of a field. Now rotate the ball so where the ant is will be directly facing the side of the field, 90 degrees rotation of the ball from facing either goal. At this specific point the ant can see each goal at each end of the field even though the ball is directly between the middle of the two goals. Well, depending how tall the ant is given the goals are so close to the ball. A huge distance is actually a helping factor in this case. A 1.75 meter person can see 4,700 away before the horizon curves out of view. That means (ignoring the bending of light by the atmosphere still) the viewing angle allows for 1 meter "down" every ~2,685.7 meters out. The radius of the Earth is ~6,371,000 meters so to be able to see the middle of an object from ~the radius of the earth "down" with that viewing angle would require the object to be a minimum of ~2,685.7 * 6,371,000 = 17,110,594,700 meters away. That's a minimum distance of ~0.11 AU so the person would only get a partial view of the moon but a full view of the sun because the moon -isn't- far enough away! Well technically the Earth could rotate slightly farther while having the middle of the sun still visible but I'm too lazy to calculate if it's actually enough, my hunch is no. If you wanted to see the middle of the moon and the middle of the sun (with no bending by the atmosphere) during an eclipse you'd have to be near the top of Everest while it happens to be exactly rotated between each.
  - tobr 4y ago
    So are you saying that the offset of 1 Earth/soccer ball radius is helping or hurting? It’s still seems to me like it’s just getting in the way. (Though I guess the ant wouldn’t see much of anything if it was down in the grass.)
    - IanCal 4y ago
      It helps you see things either side of the ball if you're offset from the centre. Forgive the hasty diagram but https://imgur.com/a/aoZIZTs https://imgur.com/a/aoZIZTs The Earth is entirely in-between the wildly out of scale Sun and the Moon, but a giant standing on the "top" of the Earth can see both.

tobr 4y ago

That is interesting… but to my intuition, it seems like that would have the opposite effect? You are offset in the “wrong” direction, ie the sun and the moon are further “down” and more obscured by the earth? I might be thinking all wrong about this, though. I’d also question if this can have any meaningful effect on the sun, which is about 23500 Earth radii away. That’s a very, very slight perspective shift.

zamadatix 4y ago
Imagine an ant standing on some random point on a soccer ball in the middle of a field. Now rotate the ball so where the ant is will be directly facing the side of the field, 90 degrees rotation of the ball from facing either goal. At this specific point the ant can see each goal at each end of the field even though the ball is directly between the middle of the two goals. Well, depending how tall the ant is given the goals are so close to the ball. A huge distance is actually a helping factor in this case. A 1.75 meter person can see 4,700 away before the horizon curves out of view. That means (ignoring the bending of light by the atmosphere still) the viewing angle allows for 1 meter "down" every ~2,685.7 meters out. The radius of the Earth is ~6,371,000 meters so to be able to see the middle of an object from ~the radius of the earth "down" with that viewing angle would require the object to be a minimum of ~2,685.7 * 6,371,000 = 17,110,594,700 meters away. That's a minimum distance of ~0.11 AU so the person would only get a partial view of the moon but a full view of the sun because the moon -isn't- far enough away! Well technically the Earth could rotate slightly farther while having the middle of the sun still visible but I'm too lazy to calculate if it's actually enough, my hunch is no. If you wanted to see the middle of the moon and the middle of the sun (with no bending by the atmosphere) during an eclipse you'd have to be near the top of Everest while it happens to be exactly rotated between each.
- tobr 4y ago
  So are you saying that the offset of 1 Earth/soccer ball radius is helping or hurting? It’s still seems to me like it’s just getting in the way. (Though I guess the ant wouldn’t see much of anything if it was down in the grass.)
  - IanCal 4y ago
    It helps you see things either side of the ball if you're offset from the centre. Forgive the hasty diagram but https://imgur.com/a/aoZIZTs https://imgur.com/a/aoZIZTs The Earth is entirely in-between the wildly out of scale Sun and the Moon, but a giant standing on the "top" of the Earth can see both.