The Sun and the Moon are about the same size when you look at them in the sky, though that’s
just thanks to the coincidence that the Sun is about 400 times farther away than the Moon
and also about 400 times bigger. Another fun coincidence is that the radius of the Sun
is about twice the distance to the moon, so if you put the sun where the Earth is,
the Moon would be just over halfway to the surface of the Sun.
而且 由于太阳太大 光线需要4.5秒多才能穿过它的表面
The Sun is also so big that it takes light over 4 and a half seconds to travel across
its face – though I don’t know whether that says more about how big the Sun is, or how
slow light is, or both.
What about the scale of other solar system objects? Well, here are Pluto and Charon compared
to the Earth and the Moon.
至于木星 一般来说 它的半径大约是地球的10倍
And Jupiter; which, as a rough rule of thumb, has about 10 times the radius of the earth
and one tenth the radius of the Sun.
Saturn is slightly smaller than Jupiter, though its rings go out twice as far – still only
a third of the way to the Moon, though.
Mars’ moons are very close and very small, which gives rise to another moon-sized coincidence:
从火星上看 火星和太阳大小相近 同时也会出现周期性日食
Phobos is almost the same size in the martian sky as the Sun, and can cause annular eclipses
just like our Moon here on Earth.
If two objects have the same apparent size in the sky, like the Moon and the Sun, it
It means that their radius divided by their distances is about the same value.This also implies
that the strengths of the objects’ tidal forces, which are roughly proportional to
the radius over the distance cubed, will also be about the same. In fact, ANY two objects
of roughly the same density that look about the same size in the sky will have tidal forces
of similar strengths.
So while the apparent equal size of the moon and sun in our sky is a coincidence, the fact
that they have similar apparent sizes and roughly similar effects on the tides is a
consequence – of geometry