Wikipedia:Main Page history/2019 June 15
From today's featured articleAdam Eckfeldt (June 15, 1769 – February 6, 1852) was the second chief coiner of the United States Mint. His father owned a large smithy and involved himself in early attempts at American coinage. Eckfeldt built early presses for the Mint, engraved some of its early dies, and was responsible for some designs of early American copper pieces, as well as the 1792 half disme, which some authorities consider the first United States coin. He was appointed assistant coiner of the Mint in 1796, and became chief coiner after his predecessor's death in 1814. During Eckfeldt's tenure, the Philadelphia Mint moved to new premises and expanded its operations. Setting aside unusual coins that were brought in as bullion, he started the Mint's coin cabinet, which evolved into the National Numismatic Collection. Despite his 1839 retirement, Eckfeldt continued performing the duties of chief coiner until his death, though his successor, Franklin Peale, bore the title. (Full article...)
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On this dayJune 15: International Surfing Day (2019)
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A binary black hole is a system consisting of two black holes in close orbit around each other. For many years, proving the existence of such binaries was made difficult because of the nature of black holes themselves and the limited means of detection available. However, in the event that a pair of black holes were to merge, an immense amount of energy should be given off as gravitational waves, with distinctive waveforms that can be calculated using general relativity. This video is a computer simulation of the binary black hole system GW150914 during its final inspiral, merge and ringdown, as it would have been seen by a nearby observer. The star field behind the black holes is heavily distorted and appears to rotate and move, due to extreme gravitational lensing caused by spacetime being warped by the orbiting black holes. This event, observed by LIGO in 2015, was the first observation of a binary black hole merger, as well as the first direct detection of gravitational waves, confirming Einstein's predictions. Video credit: Simulating eXtreme Spacetimes
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