土星环与土星的季节
Rings and Seasons of Saturn
Image Credit & Copyright: Damian Peach/SEN
Explanation: On Saturn, the rings tell you the season. On Earth, Wednesday marks an equinox, the time when the Earth’s equator tilts directly toward the Sun. Since Saturn’s grand rings orbit along the planet’s equator, these rings appear most prominent — from the direction of the Sun — when the spin axis of Saturn points toward the Sun. Conversely, when Saturn’s spin axis points to the side, an equinox occurs and the edge-on rings are hard to see from not only the Sun — but Earth. In the featured montage, images of Saturn between the years of 2004 and 2015 have been superposed to show the giant planet passing from southern summer toward northern summer. Saturn was as close as it can get to planet Earth last month, and this month the ringed giant is still bright and visible throughout much of the night
Tomorrow’s picture: dark nebula 1251
土星环与土星的季节
影像提供与版权: Damian Peach/SEN
说明: 土星环是土星季节的指标。而在地球上，这个星期二是地球的分点（秋分），是地球赤道侧向太阳的时候。因为土星宏伟的环系环绕这颗行星的赤道，从太阳的方向看过，当土星自转轴倾向太阳之时，行星环最为显著突出。反过来说，当土星的自转轴侧对着太阳，时值分点之时，此时从太阳和地球的方向看过来，侧向的土星环很难辨识。这幅主题影像叠加自在2004年到2015年之间所拍摄的土星照片，用以呈现这颗巨行星从南半球夏季至北半球夏季的转换。虽然土星冲是在上个月，不过这个月的土星依旧非常明亮而且彻夜可见。
明日的图片: dark nebula 1251
