2025年3月25日
A Blue Banded Blood Moon
Image Credit & Copyright: Zixiong Jin
Explanation: What causes a blue band to cross the Moon during a lunar eclipse? The blue band is real but usually quite hard to see. The featured HDR image of last week’s lunar eclipse, however — taken from Norman, Oklahoma (USA) — has been digitally processed to exaggerate the colors. The gray color on the upper right of the top lunar image is the Moon‘s natural color, directly illuminated by sunlight. The lower parts of the Moon on all three images are not directly lit by the Sun since it is being eclipsed — it is in the Earth’s shadow. It is faintly lit, though, by sunlight that has passed deep through Earth’s atmosphere. This part of the Moon is red — and called a blood Moon — for the same reason that Earth’s sunsets are red: because air scatters away more blue light than red. The unusual purple-blue band visible on the upper right of the top and middle images is different — its color is augmented by sunlight that has passed high through Earth’s atmosphere, where red light is better absorbed by ozone than blue.
Celestial Surprise: What picture did APOD feature on your birthday? (post 1995)
Tomorrow’s picture: star factory
披着蓝色光带的红月
影像提供与版权: Zixiong Jin
说明: 月食期间为何月面会出现蓝色的光带？这道蓝色光带是真的，但通常不易见到。然而，这张在上星期的月食期间，摄于美国奥克拉荷马州诺曼市的高动态范围主题影像，特别经过数位处理以夸大月面的颜色变化。在最上方月球照片右上角的灰色区域，受到了阳光的直射，故带着月球的自然色彩。不过，这3张影像里的月球下半部，皆沉浸在地球的影子，是为食缺未受到阳光直射的区域。然而，此处的月面仍会散发微光，而照耀它们的，则是深入地球大气的阳光所造就的地球反照光。因此，这部分的月面色泽泛红，故有“血月”之称；它们红化的原因与地球见到的火红落日雷同，源自地球大气散射的蓝光多于透过的红光所致。在最上方及中间的影像里，还可见到不寻常的紫蓝色光带；这种颜色的形成机制不同，其色泽来自穿过地球高层大气的阳光，受到该处的臭氧吸收之红光多于蓝光，致使部分月面披着蓝紫色的光带。
天体惊喜: 你生日那天APOD展示了什么照片？（1995年后）
明日的图片: star factory
