秋分的天空

2020年9月22日

Equinox in the Sky
Image Credit & Copyright: Luca Vanzella

Explanation: Does the Sun set in the same direction every day? No, the direction of sunset depends on the time of the year. Although the Sun always sets approximately toward the west, on an equinox like today the Sun sets directly toward the west. After today’s September equinox, the Sun will set increasingly toward the southwest, reaching its maximum displacement at the December solstice. Before today’s September equinox, the Sun had set toward the northwest, reaching its maximum displacement at the June solstice. The featured time-lapse image shows seven bands of the Sun setting one day each month from 2019 December through 2020 June. These image sequences were taken from Alberta, Canada — well north of the Earth’s equator — and feature the city of Edmonton in the foreground. The middle band shows the Sun setting during the last equinox — in March. From this location, the Sun will set along this same equinox band again today.

Tomorrow’s picture: open space

秋分的天空
影像提供与版权: Luca Vanzella

说明: 太阳都在相同的方位西沉吗？并不是，日落的方位会随日子而异。太阳大致上落向西方，不过只有在今天这种分点时，日落的方向才是正西。今天的秋分过后，太阳西落的位置会逐日向西南偏移，在12月的冬至移到最西南的位置。在今天的秋分之前，日落的的位置在西偏北，6月夏至那天的日落最靠西北。这幅主题缩时影像，呈现从2019年12月至2020年6月，每个月一道共7道的日落迹线。这些影像系列，皆是摄于远在地球赤道北方的加拿大·艾伯塔省，故位在前景的埃德蒙顿市清楚可见。最中间的迹线，则是去年3月春分那天的日落。从这个地点看出去，今天的太阳也会再次沿春分那天的迹线西沉。

明日的图片: open space