Lunar Eclipse
Did you see the lunar eclipse on Saturday night? Lunar eclipses occur when the earth blocks the sun’s light by passing between the sun and the moon and we see the earth’s shadow gradually cast across the moon. Although lunar eclipses are not particularly rare, with a clear sky, as on Saturday night, the sight of the moon with a red or copper hue is an impressive sight.
The Folio records accounts observing both solar and lunar eclipses and, interestingly, these were viewed as sufficiently important to be included in the index to the Folio. Such accounts tended to be in the form of letters, for instance in July 1782, Cassini writes to Flamstead, describing an eclipse of the moon in Dantizick, whilst in December 1685, Hevlius writes to Aston ,again with an account of a lunar eclipse in Dantizick. These descriptions are not confined to the Hooke Folio, however, and form part of a wider pattern of interest in lunar eclipses within the early Royal Society. For example accounts of eclipses are sent from various places including Paris and Moscow, whilst in 1666, Gresham-Professor of Geometry Mr Rook’s methods for observing a lunar eclipse are published in the Society’s Philosophical Transactions. He says that the observer, preferably using a telescope rather than the naked eye, should pick out three of the ‘eminentest spots’ which ‘lie nearest the ecliptick’ and note the time a shadow is first cast on each one and when they are ‘completely entered in’ and out of the shadow. Rook also comments that observing lunar eclipses is important, not only for the astronomical information that could be gleaned, but also for the geographical information, such as comparing how observations made by scientists in various countries both differed and converged.
If you missed Saturday’s eclipse, one should be visible (weather permitting) on July 16th, though only if you live in Asia, the Pacific or the West of the Americas, if you live in Europe then you’ll have to wait until 9th January.
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