APOD:2015.9.23

Sweet丿Kim (金) 天王星
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发表于:2015-09-24 13:08 [只看楼主] [划词开启]

南极洲的日行迹 

影像提供与版权:

Adrianos Golemis

说明: 

太阳每天都会回到天空的同一点吗?不会。此问题较佳也较视觉化的答案是一则日行迹,一种在一年之中,从同一地点同一时间所拍摄影像的组合图。上面这则主题影像,是冒着低温顶着强风在南极Concordia站附近所记录的日行迹。在许多天下午4点所拍摄的这张数位组合影像,咸信是首张南极的日行迹图。


影像之所以只呈现9月到3月的太阳位置,缘自其他日子太阳都位在地平面之下。事实上,因为今天是分点,所以南极的太阳是在消失6个月之后首次冒头,然后要到明年3月的春分,日落才会再次降临;当然,如果没受到显著的太气折射效应干扰的话。反过来说,北极在连续6个月阳光普照之后,今天会迎来落日。对地球其他介于南北极之间的区域,"分"意指今天白画和黑夜的长度都是12小时。(analemma 日行迹~)

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Antarctic Analemma 

Image Credit & Copyright: Adrianos Golemis

Explanation: Does the Sun return to the same spot on the sky every day? No. A better and more visual answer to that question is an analemma, a composite image taken from the same spot at the same time over the course of a year. The featured weekly analemma was taken despite cold temperatures and high winds near the Concordia Station in Antarctica. The position of the Sun at 4 pm was captured on multiple days in the digital composite image, believed to be the first analemma constructed from Antarctica. The reason the image only shows the Sun from September to March is because the Sun was below the horizon for much of the rest of the year. In fact, today being an equinox, the Sun rises today at the South Pole after a six month absence and won't set again until the next equinox in March, baring large atmospheric refraction effects. Conversely, today the Sun sets at the North Pole after half a year of continuous daylight. For all of the Earth in between, though, the equinox means that today will have a nighttime and daytime that are both 12 hours long.





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分类: 宇宙观光属

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