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Cosmology and Large Scale Structure of the Universe Print E-mail

Measurement of the Solar Diameter with SDS Telescope and Total Eclipses

On a secular basis the variation of the solar diameter of few part over 10000 can be direct responsible of the climate changes on the Earth. Its measurement with a relative accuracy of one part in a million is the goal of SDS, Solar Disk Sextant balloon borne Italian-American mission (NASA, Yale, Tor Vergata, Osservatorio Astronomico di Roma and ICRA). We already have 4 eight-hours flights in fall '92, '94 [1], '95 and '96 not completely reduced, and data from total solar eclipses of '84, '94 [2], '95, '98 and '99 observed from the edges [3] which partially overlap the SDS sampling and can provide an absolute calibration for SDS with an accuracy of one part over 10000.
The analysis program Baily Beads [4] for reducing the eclipse data will be calibrated with the previous best ephemeris program [2] and it will be applied to the eclipse data from 1567 up to now. The eclipses of 2001 December and 2002 June will be also observed. In parallel all SDS data will be reduced. The first results both on secular time scales and on the last decade are expected in 2002.

[1] Sofia, S.; Heaps, W.; Twigg, L.; Lydon, T. J.; Sofia, U. J., Results of the September 26, 1994 Balloon Flight of the Solar Disk Sextant: Implications for the Variability of the Solar Diameter and Oblateness,
American Astronomical Society Meeting, 185, #44.07 (1994).
[2] Fiala, Alan D.; Dunham, David W.; Sofia, Sabatino,
Variation of the solar diameter from solar eclipse observations, 1715-1991,
Solar Physics, vol. 152, no. 1, p. 97-104 (1994).
[3] Dunham, David W.; Bixby Dunham, Joan, Observing Total Solar Eclipses from Near the Edge of the Predicted Path,
Lunar Dynamics and Observational Coordinate Systems, Proceedings of IAU Colloq. 24, held in Houston, TX, 15-17 January, 1973. Moon 8, 1973. Revised abstracts published as Lunar Sci. Inst. Contrib. 135. Edited by M. Moutsoulas, p.546 (1973).
[4] Herald, D., Correcting predictions of solar eclipse contact times for the effects of lunar limb irregularities, Journal of the British Astronomical Association, vol.93, no.6, p.241-246 (1983).
Baily Beads Program: http://www.lunar-occultations.com/iota/winocc.htm
Among the studies on secular solar variability the case of the total-annular solar eclipse of 1567 is the most intriguing and interesting. The current scientific debate on this case still requires historical analysis: a few, undemonstrated, hypotheses on the methods of observation have been used to discriminate the nature of that eclipse (annular or total) [5].
[5] "The solar eclipse observed by Clavius in A.D. 1567", Astronomy and Astrophysics, 322, p.347-351 (1997).
If the eclipse of 1567 was really annular, as Clavius stated, it imply that the Sun in 1567 was larger than nowadays. In addition to a better knowledge of the methods of observation before the invention of the telescope see e.g. [6], this study has some important implications in our understanding of solar astrophysics and, consequently, in terrestrial meteorology.
[6] "Measurements of the Solar Diameter in Kepler's Time", Costantino Sigismondi and Federico Fraschetti; The Observatory Vol. 121 (2001) 380-385. http://www.ulo.ucl.ac.uk/obsmag/              ftp://www.icra.it/dataext/sigismondi/Obs2001.pdf.

Variable Stars

Also we are investigating, in collaboration with Prof. Dorrit Hoffleit, Yale University and Riccardo Coccioli (Physics Student at "La Sapienza"), the Long-term behavior of Mira-type variable stars. This problem, naturally related to the solar variability, presents some new aspects on the study of the time series of maxima: there exist negative correlations between the luminosity of two consecutive maxima.

[7] "Long-term Behavior of Mira Ceti Maxima", Costantino Sigismondi, Dorrit Hoffleit and Riccardo Coccioli; Presented in the 90th AAVSO meeting in Madison (WI) and published in JAAVSO, The Journal of American Association of Variable Stars Observers, (2001).  ftp://www.icra.it/dataext/sigismondi/miraAAVSO9.pdf .
[8] "Mira and the Star of Bethlehem" C. Sigismondi, http://www.quodlibet.net/sigismondi-mira.shtml Online Journal of Christian Theology and Philosophy, vol. 4 n. 1  (2002).

Lunar Impacts

The studies on Lunar Impacts [9-10] and Dynamics of Small Bodies in Solar System [11] is carried out with Giovanni Paolo Imponente (ICRA and Napoli University) and David W. Dunham (Johns Hopkins University, Applied Physics Laboratory). We posed and studied the problem of luminous efficiency of hypervelocity impacts [12] and we are opening now the collaboration with other European and American partners. This problem is related with the nature and the number of the impactors, this is the reason why we are studying also the dynamic of the Leonids, meteoroids originated by the Comet P/Tempel-Tuttle [11].

[9] "The observation of Lunar Meteors", C. Sigismondi and G. Imponente, WGN, the Journal of the IMO, vol. 28 n. 2/3, p. 54-57 (2000).      http://babbage.sissa.it/abs/astro-ph/0006210
[10] "The observation of Lunar Meteors II." C. Sigismondi and G. Imponente, WGN, the Journal of the IMO, vol. 28 n. 6, p. 230-232 (2000). http://babbage.sissa.it/abs/astro-ph/0105226
[11] "Ejection Velocity of Meteoroids from Comet Surfaces", Giovanni Imponente and Costantino Sigismondi; WGN, The Journal of the IMO, vol. 29, No. 5 (2001) 176-181.   ftp://www.icra.it/dataext/sigismondi/WGN295c.pdf .
[12] "The Luminous Efficiency of Hypervelocity Impacts on the Moon", Costantino Sigismondi and David W. Dunham; New Views of the Moon, Europe Future Lunar Exploration, Science Objectives, and Integration of Datasets, David Heather editor, Berlin, Germany (2002).             ftp://www.icra.it/dataext/sigismondi/NVE_2002.pdf .

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