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Astronomical Topics

Nature volume 130, page 371 (03 September 1932) | Download Citation



The Corona without an Eclipse.—L'Astronomie for June contains an article by M. B. Lyot, giving further particulars about his results obtained at the Pic du Midi. He states that the brightness of the inner corona is about equal to that of the planet Mars, which is readily visible in daylight; but observation of the corona is rendered more difficult by the great brightness of the sky near the sun; this is, however, greatly diminished at a height of 10,000 feet, especially when cloud and dust are absent; a further difficulty, due to diffused light in the telescope, is diminished by keeping the lenses quite free from dust, and by placing diaphragms in the tube, slightly larger than the solar image, to shut off sunlight. In order to distinguish instrumental defects from genuine solar markings, the coronagraph was rotated slightly between exposures; instrumental markings remain in the same place on the plate, but solar ones follow the solar image. Using a red screen, it was possible to view prominences directly, without a spectroscope; a Wratten screen, transmitting light between wave-lengths 6500 and 6600, permitted photographs to be taken of coronal jets, rising to a height of 7′ above the sun's limb.

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