日出天空的暗影

2024年9月21日

Sunrise Shadows in the Sky
Image Credit & Copyright: Emili Vilamala

Explanation: The defining astronomical moment of this September’s equinox is at 12:44 UTC on September 22, when the Sun crosses the celestial equator moving south in its yearly journey through planet Earth’s sky. That marks the beginning of fall for our fair planet in the northern hemisphere and spring in the southern hemisphere, when day and night are nearly equal around the globe. Of course, if you celebrate the astronomical change of seasons by watching a sunrise you can also look for crepuscular rays. Outlined by shadows cast by clouds, crepuscular rays can have a dramatic appearance in the twilight sky during any sunrise (or sunset). Due to perspective, the parallel cloud shadows will seem to point back to the rising Sun and a place due east on your horizon on the equinox date. But in this spectacular sunrise skyscape captured in early June, the parallel shadows and crepuscular rays appear to converge toward an eastern horizon’s more northerly sunrise. The well-composed photo places the rising Sun just behind the bell tower of a church in the town of Vic, province of Barcelona, Catalonia, Spain.

Tomorrow’s picture: Equinox in the City

日出天空的暗影
影像提供与版权: Emili Vilamala

说明: 今年9月的秋分，天文学上落在世界时9月22日的12:44，当太阳在地球天空的年度旅程中，往南越过天球赤道的那刻。秋分则标志了地球北半球的秋天及南半球春天的起点，而在这天，全球各地的白昼与黑夜几乎等长。如果你是以观赏日出的方式，来庆祝天文学上的季节变化，不妨也找找云隙光。云隙光是由云朵投射的阴影所勾勒出的光束，尤其在日出（或日落）暮曙光时分的天空中格外醒目。由于透射效应，相互平行的云朵阴影看似指向日出点，而在秋分这天，此点位于正东的地平线上。不过，在这张摄于6月初的壮丽日出天空影像里，平行的暗影和云隙光，则看似会聚在偏北的东方地平线日出点上。在这幅精心构建的日出影像里，东升的太阳，则位于西班牙加泰隆尼亚自治区巴塞罗那省维克镇的教堂钟楼后方。

明日的图片: Equinox in the City