Mercurys Sodium Tail

Explanation: That's no comet. Below the Pleiades star cluster is actually a planet: 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 atoms 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 last week from La Palma, Spain 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 spacecraft that orbited Mercury between 2011 and 2015. Tails, of course, are usually associated with comets.

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Explanation: The parade continues. In the pre-dawn sky, the planets Jupiter, Venus, Mars, and Saturn have been visible. The planets were captured over the Step Pyramid of Djoser in the featured image taken last month. One of the oldest pyramids in Egypt is located in the Saqqara necropolis and was built in the 27th century BC. A foreground image was taken during the evening blue hour and a background image was taken the following morning. The morning planet line-up is slowly changing. At the end of last month, planets Jupiter and Venus switched places, and at the end of this month, planets Jupiter and Mars will switch places. All of these worlds continue to circle the Sun as they have for billions of years before the Pyramid of Djoser was built.