2025年4月29日
Saturn’s Rings Appear to Disappear
Image Credit & Copyright: Natan Fontes
Explanation: Where are Saturn’s ears? Galileo is credited, in 1610, as the first person to see Saturn’s rings. Testing out Lipperhey‘s recently co-invented telescope, Galileo did not know what they were and so called them “ears“. The mystery deepened in 1612, when Saturn’s ears mysteriously disappeared. Today we know exactly what happened: from the perspective of the Earth, Saturn’s rings had become too thin to see. The same drama plays out every 15 years because Saturn, like Earth, undergoes tilt-driven seasons. This means that as Saturn goes around the Sun, its equator and rings can tilt noticeably toward the Sun and inner Solar System, making them easily visible, but from other orbital locations will appear almost not at all. The featured picture from Brasilia, Brazil shows a modern version of this sequence: the top ring-dominated image was taken in 2020, while the bottom ring-obscure image taken earlier in 2025.
Make Saturn’s Rings Musical: Play them like a harp!
Tomorrow’s picture: smiling sky
土星环消失之谜
影像提供与版权: Natan Fontes
说明: 土星的”耳朵”在那？伽利略咸认是在1610年目睹土星环的第一人。当时伽利略在测试Lipperhey（利伯希）共同发明的望远镜，不过，他不知见到的是什么，所以暂且称之为“耳朵”。在1612年，当土星的耳朵神秘的消失时，为“耳朵之谜”带来更多迷雾。现今的我们完全知道土星环消失的真象，只缘从地球看出去，土星环系变得太纤薄而不得见而已。这种景象每15年会出现一次，因为土星和地球类似，有因自转轴倾斜所造成的季节变化。也就是说，随着土星绕太阳公转，当它的赤道和环系倾向太阳及太阳系内围时，它的环系变得鲜明易见，然而在某些轨道位置，环系会看似完全消失。这张摄于巴西首都巴西利亚市的主题照片，呈现了记录上述景象的现代版本；在顶端，环系比土星本体还要壮观的影像摄于2020年，而底端环系几乎消失的影像，则摄于2025年。
让土星环充满音乐: 像弹奏竖琴一样演奏它们！
明日的图片: smiling sky
