土星与六颗卫星

2021年07月06日

Saturn and Six Moons
Image Credit & Copyright: Mohammad Ranjbaran; MR Thanks: Amir Ehteshami

Explanation: How many moons does Saturn have? So far 82 have been confirmed, the smallest being only a fraction of a kilometer across. Six of its largest satellites can be seen here in a composite image with 13 short exposure of the bright planet, and 13 long exposures of the brightest of its faint moons, taken over two weeks last month. Larger than Earth’s Moon and even slightly larger than Mercury,Saturn’s largest moon Titan has a diameter of 5,150 kilometers and was captured making nearly a complete orbit around its ringed parent planet. Saturn’s first known natural satellite, Titan was discovered in 1655 by Dutch astronomer Christiaan Huygens, in contrast with several newly discovered moons announced in 2019. The trail on the far right belongs to Iapetus, Saturn’s third largest moon. The radius of painted Iapetus’ orbit is so large that only a portion of it was captured here. Saturn leads Jupiter across the night sky this month, rising soon after sunset toward the southeast, and remaining visible until dawn.

Tomorrow’s picture: through orion

土星与六颗卫星
影像提供与版权: Mohammad Ranjbaran; MR Thanks: Amir Ehteshami

说明: 土星有多少颗卫星？目前获得确认的有82颗，最小者的宽度远小于1公里。在这幅由摄于上个月最后二星期的13张短曝光土星照片组合而成的影像里，可见到土星的6颗大卫星。其中，比月亮大、更稍大于水星、直径高达5,150公里的土星最大卫星土卫六，几乎环绕这颗带环母行星一圈。由荷兰天文学家惠更斯于1655年发现的土卫六，是人类找到的第一颗土星天然卫星，而相较之下，有数颗土星的新卫星，发布的日期近在2019年。影像右缘的迹线来自土星第三大的卫星─土卫八。色彩缤纷的土卫八轨道非常宽广，因此这幅影像只记录轨道的一小部分。在这个月刚日落之后，土星会比木星早从东南方升起，带头移过夜空并且在日出前皆可见。 （Titan 土卫六；Iapetus 土卫八）

明日的图片: through orion