南天的二颗彗星

2022年10月8日

Two Comets in Southern Skies
Image Credit & Copyright: Jose J. Chambo (Cometografia)

Explanation: Heading for its closest approach to the Sun or perihelion on December 20, comet C/2017 K2 (PanSTARRS) remains a sight for telescopic observers as it sweeps through planet Earth’s southern hemisphere skies. First time visitor from the remote Oort cloud this comet PanSTARRS sports a greenish coma and whitish dust tail about half a degree long at the upper left in a deep image from September 21. It also shares the starry field of view toward the constellation Scorpius with another comet, 73P/Schwassmann-Wachmann 3, seen about 1 degree below and right of PanSTARRS. Astronomers estimate that first time visitor comet C/2017 K2 (PanSTARRS) has been inbound from the Oort cloud for some 3 million years along a hyperbolic orbit. Schwassmann-Wachmann 3 is more familiar though. The periodic comet loops through its own elliptical orbit, from just beyond the orbit of Jupiter to the vicinity of Earth’s orbit, once every 5.4 years. Just passing in the night, this comet PanSTARRS is about 20 light-minutes from Earth in the September 21 image. Seen to be disintegrating since 1995, Schwassmann-Wachmann 3 was about 7.8 light-minutes away.

Tomorrow’s picture: northern skylights

南天的二颗彗星
影像提供与版权: Jose J. Chambo (Cometografia)

说明: 在地球南天飞掠，将在12月20日抵达近日点的泛星彗星（C/2017 PanSTARRS），仍然是望远镜观星者巡天的好目标。在这幅摄于9月21日的深空影像里，来自遥远欧特云的首航彗星泛星，是影像左上角那个曳着泛绿彗发及约半度长泛白尘尾的天体。与它分享这片天蝎座天空视野的，还有它右下方相隔约1度、名为施瓦斯曼-瓦赫曼3号（73P/Schwassmann-Wachmann 3）的另一颗彗星。天文学家估计首次到访的彗星C/2017 K2（泛星），循着双曲线轨道从欧特云入境已飞行了约300万年。不过，我们对施瓦斯曼-瓦赫曼3号彗星则较熟悉。这颗周期彗星，沿着稍远于木星及地球附近的椭圆轨道，每5.4年环绕一圈。在9月21日那晚拍下的这幅影像时，泛星彗星距离地球约20光分。而自1995年以来就开始解体的施瓦斯曼-瓦赫曼3号彗星，距离我们则约有7.8光分。

明日的图片: northern skylights