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6月21日太阳的最高点

你需要太阳的开销在6月21日中午最高?

由于太阳的光线垂直于北回归线6月21日,太阳不应该在这个位置中午吗?

回答

* *的,这取决于你真正的意思。* *我们被相当模糊的条款,因此它不应该惊讶如果答案不符合我们的预期。我们可以解释所有这些术语来得出结论,这种情况只会很少,甚至从未发生。但允许一些合理的纬度(原谅双关语)在我们的定义,我们可以想出一个合理的回应“是”。太阳只能在一个地方的“头顶”,地球中心之间的界线和太阳与地球的表面。因为地球绕着它的轴旋转,也朝着它的轨道,这是不断变化的纬度和经度。北回归线不是单点“位置”,但一个圈,绕着地球转。在的确切时刻(夏至)(https://en.wikipedia.org/wiki/Summer_solstice),太阳是头顶一个点在北回归线上* * *,只* * *一个点。这一点慢慢螺旋穿过热带地区,直到达到南回归线上的相应的点在冬至。然后它开始这次旅行回来了。 That's what happens in the geometrically-idealized definition of "directly overhead". We can allow a small tolerance, and as the tolerance gets bigger, the spot of "direct overheadness" spreads out into a disk, which covers more and more of the Tropic of Cancer around the moment of the Solstice, due to the spot's E-W motion being much greater than its N-S motion. Although the spot's change in latitude over time isn't linear , it's a reasonable approximation for this exercise. The spot moves about 0.18 degrees north or south in a day, all the while circling the Earth. Around the Solstice it will move 0.09 degrees north and 0.09 south. The Sun's angular size in the sky is 0.5 degrees, so, it's reasonable to conclude that yes, the Sun is directly overhead every point of the Tropic of Cancer ***at some time around the summer solstice***. (The solstice does't always happen on June 21, but depending on the tolerance, some degree of direct-overheadness will be the situation for a few days before and after the solstice). So now, we get to your last two tricky terms: "noon" and "June 21" , which believe it or not are in conflict for this example. There is a local "noon" (defined by when the Sun is the highest in the sky it can get) and a clock "noon" (defined by your time zone). Only people at lucky longitudes in their time zones get to have them coincide. But "June 21" is defined by those very time zones. And so the sun can be "directly overhead" at "noon" on June 21 only around those lucky meridians. Elsewhere the sun will be directly overhead at some time other than noon.

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