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An eclipse is such an amazing phenomenon. The last time it happened I had my mind blown by a simple realization: There is no physical reason why the moon fits

by scop 6y ago

An eclipse is such an amazing phenomenon. The last time it happened I had my mind blown by a simple realization: There is no physical reason why the moon fits precisely within the diameter of the sun. It just so happens that on our little planet with sentient life, in which human life is present for only an incredibly small window, the time in which we are present and looking to the skies is when the diameter and distances of the sun and moon align so perfectly as to fit one within the other.

wruza 6y ago
Uhm, I should check my trig before making claims, but it feels like there is a pretty big moon diameter range between making a non-zero dark spot on the earth (size too small) and covering all of the corona effects (size too big). Now it casts a pretty thick full eclipse shadow, so it isn't well aligned to fit the sun — it hides part of the corona too, when you're at the center.
praveen9920 6y ago
Actually, It doesn't exactly fits, it appears to fit from some perspectives. Sun's size is so big comparable to both earth and moon. When shadow of moon is spread on earth, shadow's radius is much smaller than moon's radius, unlike our conventional knowledge that shadows appear larger with distance. For people on earth who are in the path of totality, it appears as if moon has completly covered the sun.
saas_sam 6y ago
This is a true mind-blowing fact. The ratio of the distances between Earth-Sun and Earth-Moon is close to the ratio of the sizes between Sun & Moon. So the Moon & Sun look to be the same apparent size from the perspective of Earthlings... When I last read about this, we hadn't identified any other moons for which this holds true. It turns out our moon has many seemingly strange properties. It's big but not very dense. Still a bit of a mystery how it formed, too. There are leading theories (ex. Mars-sized planet ramming into a young Earth) but not considered settled science just yet IIRC.
- soulofmischief 6y ago
  We have no idea how lucky we are and we're destroying our planet and the life within. There are probably so many things about our situation which we take for granted, many things with infinitesimally small chances of occurring even within just systems harboring sentient life. The number of systems which reach our intellectual capacity must all have certain aspects which make them completely unique, a rare feat in such a large and repetitive universe.
- kyuudou 6y ago
  Widen out the scope a bit and you see Bode's law[1] all the way out to Neptune. 1: https://en.wikipedia.org/wiki/Titius%E2%80%93Bode_law https://en.wikipedia.org/wiki/Titius%E2%80%93Bode_law
earthboundkid 6y ago
This is a funny thing about science. The ancients totally had an "explanation" of why the sun and the moon are the same size. Naturally, because the sun is highest form of yang energy, the moon must be the highest form of yin energy, etc. Modern science, OTOH, doesn't recognize this is a question to be explained. It's an example of how if your system doesn't have a place for something, you don't even notice the absence.
interfixus 6y ago
> There is no physical reason why the moon fits precisely within the diameter of the sun This ought to fit nicely into some version of the anthropic principle. That either pensive critters like us specifically or life in more general terms for a variety of subtle reasons depend on just such a match of ratios.
at_a_remove 6y ago
Since the moon moves away from the earth, very slowly, in a bit over half a billion years we will have no more total eclipses.
GoblinSlayer 6y ago
If moon's size was larger than sun, then eclipses would be proper nights.

by scop 6y ago

wruza 6y ago

Uhm, I should check my trig before making claims, but it feels like there is a pretty big moon diameter range between making a non-zero dark spot on the earth (size too small) and covering all of the corona effects (size too big). Now it casts a pretty thick full eclipse shadow, so it isn't well aligned to fit the sun — it hides part of the corona too, when you're at the center.

praveen9920 6y ago

Actually, It doesn't exactly fits, it appears to fit from some perspectives. Sun's size is so big comparable to both earth and moon. When shadow of moon is spread on earth, shadow's radius is much smaller than moon's radius, unlike our conventional knowledge that shadows appear larger with distance. For people on earth who are in the path of totality, it appears as if moon has completly covered the sun.

saas_sam 6y ago

This is a true mind-blowing fact. The ratio of the distances between Earth-Sun and Earth-Moon is close to the ratio of the sizes between Sun & Moon. So the Moon & Sun look to be the same apparent size from the perspective of Earthlings... When I last read about this, we hadn't identified any other moons for which this holds true. It turns out our moon has many seemingly strange properties. It's big but not very dense. Still a bit of a mystery how it formed, too. There are leading theories (ex. Mars-sized planet ramming into a young Earth) but not considered settled science just yet IIRC.

soulofmischief 6y ago
We have no idea how lucky we are and we're destroying our planet and the life within. There are probably so many things about our situation which we take for granted, many things with infinitesimally small chances of occurring even within just systems harboring sentient life. The number of systems which reach our intellectual capacity must all have certain aspects which make them completely unique, a rare feat in such a large and repetitive universe.
kyuudou 6y ago
Widen out the scope a bit and you see Bode's law[1] all the way out to Neptune. 1: https://en.wikipedia.org/wiki/Titius%E2%80%93Bode_law https://en.wikipedia.org/wiki/Titius%E2%80%93Bode_law

earthboundkid 6y ago

This is a funny thing about science. The ancients totally had an "explanation" of why the sun and the moon are the same size. Naturally, because the sun is highest form of yang energy, the moon must be the highest form of yin energy, etc. Modern science, OTOH, doesn't recognize this is a question to be explained. It's an example of how if your system doesn't have a place for something, you don't even notice the absence.

interfixus 6y ago

> There is no physical reason why the moon fits precisely within the diameter of the sun This ought to fit nicely into some version of the anthropic principle. That either pensive critters like us specifically or life in more general terms for a variety of subtle reasons depend on just such a match of ratios.

at_a_remove 6y ago

Since the moon moves away from the earth, very slowly, in a bit over half a billion years we will have no more total eclipses.

GoblinSlayer 6y ago

If moon's size was larger than sun, then eclipses would be proper nights.