Astronomy Picture of the Day——地球投在月球上的圆形影子

HDR: Earth's Circular Shadow on the Moon 
Image Credit & Copyright: Cristian Fattinnanzi

Explanation: What could create such a large circular shadow on the Moon? The Earth. Last week's full Moon -- the Buck Moon -- was so full that it fell almost exactly in a line with the Sun and the Earth. When that happens the Earth casts its shadow onto the Moon. The circularity of the Earth's shadow on the Moon was commented on by Aristotle and so hasbeen noticed since at least the 4th century BC. What's new is humanity's ability to record this shadow with such high dynamic range (HDR). The featured HDR composite of last week's partial lunar eclipse combines 15 images and include an exposure as short as 1/400th of a second -- so as not to overexpose the brightest part -- and an exposure that lasted five seconds -- to bring up the dimmest part. This dimmest part -- inside Earth's umbra -- is not completely dark because some light is refracted through the Earth's atmosphereonto the Moon. A total lunar eclipse will occur next in 2021 May.

地球投在月球上的圆形影子

这是什么东西能在月球上投下的巨大影子？原来是地球。上周的满月是如此的圆，几乎和太阳及地球完全处于一条直线上。当这种情况发生时，地球就会在月球上投下影子。这幅照片的创新之处在于极高的曝光动态范围。这是一幅HDR合成影像，实际上是由15幅图像组合而成，包括短至1/400秒的曝光（以免过度曝光最亮的部分），以及持续5秒钟的长曝光（以便带出最暗的部分）。最暗的部分出现在地球的本影内部，但其实它也不是完全黑暗的，因为会有一些阳光被地球大气层折射到月球上。下一次月全食将发生在2021年5月。

高清原图地址：

https://apod.nasa.gov/apod/image/1907/PartialLunarEclipse_Fattinnanzi_3345.jpg

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