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Astatine is a very rare radioactive chemical element with the chemical symbol At and the atomic number 85. It occurs on Earth as the decay product of heavier elements. All its isotopes are short-lived, with half-lives of 8.1 hours or less. The element has never been viewed because a mass large enough to be seen would be immediately vaporized by the heat of its radioactivity. The bulk properties of astatine are not known with any certainty, but they have been predicted based on its similarity to the lighter halogens directly above it in the periodic table: fluorine, chlorine, bromine and especially iodine. It is likely to appear dark or lustrous and may be a semiconductor or a metal. Chemically, several anionic species of astatine are known and most of its compounds resemble those of iodine. It also shows some metallic behavior, and may be able to form a stable monatomic cation in aqueous solution, unlike the lighter halogens. (Full article...)

The Arena of Nîmes is a Roman amphitheatre situated in the French city of Nîmes. Built around 100 CE, shortly after the Colosseum in Rome, it is one of the best-preserved Roman amphitheatres in the world. It is also among the twenty largest Roman amphitheatres of the 400 in existence. It is 133 metres long (145 yd) and 101 metres wide (110 yd), with an arena measuring 68 metres by 38 metres (74 yd by 42 yd). The outer facade is 21 metres high (69 ft) with two stories of 60 arcades. This photograph of the exterior of the amphitheatre was taken in 2019.

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Astatine atom with electron shells

Kansas City Ballet dancers in Petite Mort

Dennis Schröder

Western terminus of the Northern Xinjiang railway