李奥纳德彗星的长尾

李奥纳德彗星的长尾

2022年1月3日 Comet Leonard’s Long Tail Image Credit & Copyright: Jan Hattenbach Explanation: You couldn’t see Comet Leonard’s extremely long tail with a telescope — it was just too long. You also couldn’t see it with binoculars — still too long. Or with your eyes — it was too dim. Or from a city — the sky was too bright. But from a dark location with a low horizon — your camera could. And still might — if the comet survives today’s closest encounter with the Sun, which occurs between the orbits of Mercury and Venus. The featured picture was created from two deep and wide-angle camera images taken from La Palma in the Canary Islands of Spain late last month. Afterwards, if it survives, what…

水星的钠尾

水星的钠尾

2020年7月8日 Mercury’s Sodium Tail Image Credit & Copyright: Andrea Alessandrini Explanation: What is that fuzzy streak extending from Mercury? Long exposures of our Solar System’s innermost planet may reveal something unexpected: a tail. Mercury’s thin atmosphere contains small amounts of sodium that glow when excited by light from the Sun. Sunlight also liberates these molecules from Mercury’s surface and pushes them away. The yellow glow from sodium, in particular, is relatively bright. Pictured, Mercury and its sodium tail are visible in a deep image taken in late May from Italy through a filter that primarily transmits yellow light emitted by sodium. First predicted in the 1980s, Mercury’s tail was first discovered in 2001. Many tail details were revealed in multiple observations by NASA’s robotic MESSENGER…