关于最后的日全食
本帖最后由 q5968661 于 2009-2-26 14:03 编辑http://upload.wikimedia.org/wikipedia/commons/f/f6/Eclipses_solares.en.png
A Total eclipse in the umbra（本影日全食）
B Annular eclipse in the antumbra（伪本影日环食）
C Partial eclipse in the penumbra（半影日偏食）
Diagram of solar eclipse (not to scale)
Final totality
Spectacular solar eclipses are an extreme rarity within the universe at large. They are seen on Earth because of a fortuitous combination of circumstances that are statistically very improbable. Even on Earth, spectacular eclipses of the type familiar to people today are a temporary (on a geological time scale) phenomenon. Many millions of years in the past, the Moon was too close to the Earth to precisely occult the Sun as it does during eclipses today; and many millions of years in the future, it will be too far away to do so.
Due to tidal acceleration, the orbit of the Moon around the Earth becomes approximately 3.8 cm more distant each year. It is estimated that in 600 million years, the distance from the Earth to the Moon will have increased by 23,500 km, meaning that it will no longer be able to completely cover the Sun's disk. This will be true even when the Moon is at perigee, and the Earth at aphelion.
A complicating factor is that the Sun will increase in size over this timescale. This makes it even more unlikely that the Moon will be able to cause a total eclipse. Therefore the last total solar eclipse on Earth will occur in slightly less than 600 million years.
From Wikipedia, the free encyclopedia
日（全）食在整个宇宙中不仅非常罕见，而且对地球来说也不是永有的现象（只是一时的）。随着月亮逐渐远去（每年3.8厘米）和太阳的增大，在遥远的未来（大约6亿年）月亮再也无法完全掩蔽太阳形成日全食，即使月亮在近地点地球在远日点也是如此。当然这是因为月亮离地球太远的缘故。但如果说在遥远的过去由于月亮离地球太近了而不能象现在一样“精确”地掩日形成日（全）食的话，那您认为可能的原因会是什么呢？ ::yun1::这两天英文看太多了,留个沙发明天研究~~::hairsmile:: 有请一分半超版帮忙把大意翻译一下，谢谢！::42:: 3# q5968661
你……累死我算了yct43.gif 看了下大概，是说由于潮汐加速度，月球每年大约远离地球3.8cm，预计在6亿年后，月球和地球的距离将增加23,500公里，这也就是说到了那个时候地球上将再也看不到日全食，而最多只能看到日环食了。另外，由于太阳本身的体积也在增大，这就使得最后一次看到日全食的时间比预计的6亿年还要提前一点。 谢谢超版的大概翻译！
月亮离我们越远看起来就越小，离我们越近看起来就越大。太大了（太近）对日食的形成会产生什么样的影响？ ::hairsmile::太近了，就会看到很长时间的日全食了 可以用stellarium之类的软件模拟一下，比如在月球上看地球掩日成食的情形。。。 本帖最后由 q5968661 于 2009-2-26 18:15 编辑
Many millions of years in the past, the Moon was too close to the Earth to precisely occult the Sun as it does during eclipses today; and many millions of years in the future, it will be too far away to do so.
如何理解前半句尤其是precisely occult？ 6亿年实在太遥远了 9# q5968661
难道说是那个时候只有日全食,没有日环食? 本帖最后由 robyjr 于 2009-2-27 14:49 编辑
如何理解前半句尤其是precisely occult？
这句话的意思古代月亮离地球太近而不能像现今这样精确、完整地掩盖太阳（当时的情况在地球上看月亮比太阳大很多） 12# robyjr
::070821_09.jpg:: 强~！
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