2019 December 29
Explanation: If this is Saturn, where are the rings? When Saturn’s “appendages” disappeared in 1612, Galileo did not understand why. Later that century, it became understood that Saturn’s unusual protrusions were rings and that when the Earth crosses the ring plane, the edge-on rings will appear to disappear. This is because Saturn’s rings are confined to a plane many times thinner, in proportion, than a razor blade. In modern times, the robot Cassini spacecraft orbiting Saturn frequently crossed Saturn’s ring plane during its mission to Saturn, from 2004 to 2017. A series of plane crossing images from 2005 February was dug out of the vast online Cassini raw image archive by interested Spanish amateur Fernando Garcia Navarro. Pictured here, digitally cropped and set in representative colors, is the striking result. Saturn’s thin ring plane appears in blue, bands and clouds in Saturn’s upper atmosphere appear in gold. Details of Saturn’s rings can be seen in the high dark shadows across the top of this image, taken back in 2005. The moons Dione and Enceladus appear as bumps in the rings.
说明: 如果这是土星，那土星环何在？1612年当土星的”附肢” 消失时，伽利略还莫明所以。直到该世纪末，人们才了解土星的异常隆起是土星的环，而当地球通过土星环面时，因为土星环就比例来说，要比刮胡刀片薄很多，因此其厚度远小于宽度，于是土星环就看似消失了。在现代，于2004年至2017年间探测土星的卡西尼号太空船，就经常穿过土星环面。对这现象有兴趣的西班牙业余天文学家费尔南多．纳瓦罗，从庞大的卡西尼号原始影像网路资料库，挖出了一系列穿过土星环面时所拍摄的照片。其成果，就如这幅经过裁剪并以代表色套色的数位影像所示。影像中，纤薄的土星环套成蓝色，而土星高层大气的云和云带则套成金色。而土星环的细微结构，可参见摄于2005年，投射在这幅影像顶部的黝黑影子。影像中，环面上的突起物是土星的土卫四和土卫二。