362 research outputs found
The astrometric recognition of the solar Clementine gnomon (1702)
The Clementine gnomon has been built in 1702 to measure the Earth's obliquity
variation. For this reason the pinhole was located in the walls of Diocletian's
times (305 a. D.) in order to remain stable along the centuries, but its
original form and position have been modified. We used an astrometric method to
recover the original position of the pinhole: reshaping the pinhole to a circle
of 1.5 cm of diameter, the positions of the Northern and Southern limbs have
been compared with the ephemerides. A sistematic shift of 4.5 mm Southward of
the whole solar image shows that the original pinhole was 4.5 mm North of the
actual position, as the images in the Bianchini's book (1703) suggest. The oval
shape of the actual pinhole is also wrong. Using a circle the larger solar
spots are clearly visible. Some reference stars of the catalogue of Philippe de
la Hire (1702), used originally for measuring the ecliptic latitude of the Sun,
are written next to the meridian line, but after the last restauration (2000),
four of them are wrongly located. Finally the deviation from the true North, of
the meridian line's azimuth confirms the value recovered in 1750. This, with
the local deviations of a true line, will remain as systematic error, like for
all these historical instruments.Comment: 5 pages, 2 figures. Proceedings of the Third Galileo - Xu Guangqi
meeting, October 11-15, 2011 National Astronomical Observatories - Beijing
(China) The Sun, the Stars, the Universe, and General Relativit
Low frequency seeing and solar diameter measurements
The action of the atmospheric seeing is blurring, image stretching and image
motion. This happens even to the image of the Sun which is more than half
degree wide. Low frequency seeing components affect the solar diameter values
measured either throught the drift-scan or the heliometer methods. We present
evidences of image motion and stretching down to 0.001 Hz.Comment: 6 pages, 4 figures, Proceedings of the Third Galileo - Xu Guangqi
meeting, October 11-15, 2011 National Astronomical Observatories - Beijing
(China) The Sun, The Stars, The Universe and General Relativit
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