动画: 英仙座流星雨

Animation: Perseid Meteor Shower
Visualization Credit: Ian Webster; Data: NASA, CAMS, Peter Jenniskens (SETI Institute)

Explanation: Where do Perseid meteors come from? Mostly small bits of stony grit, Perseid meteoroids were once expelled from Comet Swift-Tuttle and continue to follow this comet’s orbit as they slowly disperse. The featured animation depicts the entire meteoroid stream as it orbits our Sun. When the Earth nears this stream, as it does every year, the Perseid Meteor Shower occurs. Highlighted as bright in the animation, comet debris this size is usually so dim it is practically undetectable. Only a small fraction of this debris will enter the Earth’s atmosphere, heat up and disintegrate brightly. Tonight and the next few nights promise some of the better skies to view the Perseid shower as well as other active showers because the first quarter moon will be absent from the sky from midnight onward.

Your Sky Surprise: What picture did APOD feature on your birthday? (post 1995)

Tomorrow’s picture: meteoric sky

动画: 英仙座流星雨
视像提供: Ian Webster; 数据提供: NASA, CAMS, Peter Jenniskens (SETI Institute)

说明: 英仙座流星从何而来？它们的前世是含冰的砂砾微粒；更精确的说，英仙座流星的前身是斯威夫特-塔特尔彗星洒落在后方的碎片，这些流星体在轨道上随着这颗彗星运行并逐渐扩散。这部主题动画，呈现了整个流星体群在绕太阳轨道上的演化。当地球每年接近这个流星体群时，就会产生英仙座流星雨。在动画中，以亮点显示的彗星碎片，基本上都太暗而难以侦测。只有少部分的这些碎片会进入地球大气，受到加热，粉碎形成明亮的流星。今晚及后续数晚的夜空，将是英仙座流星雨及其他活跃流星雨出没的好舞台，因为上弦月在子夜前就会西沉匿迹。

你的天空惊喜: APOD在你生日那天展示了什么照片？（1995年后）

明日的图片: meteoric sky

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