arXiv subjects

Costantino Sigismondi

Publications and source records attributed to Costantino Sigismondi.

At least 91 records · Page 5Linked to original sources

arXiv2011

Misura del ritardo accumulato dalla rotazione terrestre, DUT1, alla meridiana clementina della Basilica di Santa Maria degli Angeli in Roma

The Clementine Gnomon is a solar meridian telescope dedicated to solar astrometry operating as a giant pinhole dark camera, being the basilica of Santa Maria degli Angeli the dark room. This instrument built in 1701-1702 by the will of pope Clement XI by Francesco Bianchini (1662-1729) gives solar images free from distortions, excepted atmospheric refraction, because the pinhole is opticsless. Similar historical instruments are in Florence (Duomo, by Toscanelli and Ximenes), Bologna (San Petronio, by Cassini), Milan (Duomo, by De Cesaris) and Palermo (Cathedral, by Piazzi). The azimut of the Clementine Gnomon has been recently referenced with respect to the celestial North pole, and it is 4'28.8"\pm0.6", a comparison with similar coeval instruments is presented. Also the local deviations from a perfect line are known with an accuracy better than 0.5 mm. With these calibration data we used the Gnomon to measure the delay of the solar meridian transit with respect to the time calculated by the ephemerides (DUT1). The growth of this astronomical parameter is compensated by the insertion of a leap second ad the end of the year in order to keep the Universal Time close to astronomical phenomena within less than a whole second. On December 31, 2008 at 23:59:59 there is one of those leap seconds leading to 23:59:60 before the new year's midnight 00:00:00, being DUT1\approx0.7 s at that date. DUT1 has been measured with an accuracy of \pm0.3 s.

astro-ph.IM↗

arXiv2011

Delta Scorpii 2011 periastron: worldwide observational campaign and preliminary photometric analysis

Delta Scorpii is a double giant Be star in the forefront of the Scorpio, well visible to the naked eye, being normally of magnitude 2.3. In the year 2000 its luminosity rose up suddenly to the magnitude 1.6, changing the usual aspect of the constellation of Scorpio. This phenomenon has been associated to the close periastron of the companion, orbiting on a elongate ellipse with a period of about 11 years. The periastron, on basis of high precision astrometry, is expected to occur in the first decade of July 2011, and the second star of the system is approaching the atmosphere of the primary, whose circumstellar disk has a H-alpha diameter of 5 milliarcsec, comparable with the periastron distance. The preliminary results of a photometric campaign, here presented in the very days of the periastron, show an irregular behavior of the star's luminosity, which can reflect some shocks between material around the two stars. The small luminosity increasement detected in the observation of 5 of July 2011 at 20 UT may suggest that the periastron phenomena are now going to start.

astro-ph.SR↗

arXiv2011

Introduction to pinhole astronomy

The observation of the Sun with a pinhole in order to check the first and the second Kepler's law has been realized for high school students. The settling of the experiment in order to minimize the errors of measure has permitted to verify the Rayleigh formula for obtaining sharpest images given the diameter of the pinhole.

astro-ph.IM↗

arXiv2011

Measuring the Earth-Sun distance during a lunar eclipse

The classical method for measure the Earth-Sun distance is due to Aristarchus and it is based upon the measure of the angle Moon-Earth-Sun when the Moon is exactly in quadrature. Such an angle is only 9 arcminutes smaller than 90 degrees, and it is very difficult to evaluate, being necessary to look directly towards the Sun. The distance Earth-Moon and the Earth's diameter are necessary ingredients in order to derive the value of the astronomical unit. This method requires also the knowledge of the Moon's distance and the Earth's diameter, but it can permit a more precise measurement of the involved angles.

astro-ph.IM↗

arXiv2011

Lo Gnomone Clementino: Astronomia Meridiana in Chiesa dal '700 ad oggi

The Clementine Gnomon is a giant pinhole dark camera dedicated to meridian solar astrometry operating in the Basilica of Santa Maria degli Angeli in Rome. Pope Clement XI ordered Francesco Bianchini (1662-1729) to build this instrument in 1701-1702. It renders solar images distortion-free, because the pinhole is optics-less. The azimut of the Clementine Gnomon has been referenced with respect to the celestial North pole, and it is 4'28.8"\pm0.6" Eastward. Also the local deviations from a perfect line are known with an accuracy better than 0.5 mm. Therefore the transit's times are systematically in delay with respect to the ephemerides. It is emphasized the opportunity of considering the Clementine Gnomon as introductory in modern astrometry besides its key role in the history of astronomy. Seeing effects on the solar image are studied using video. The need of a definitive solution in restoring the original pinhole is also shown.

astro-ph.IM↗

arXiv2011

Variable stars magnitudes estimations exploiting the eye physiology

The physiology of the dark adaption process of the eye is revisited from an astronomical point of view. A new method for the magnitude estimation of a star is presented. It is based upon the timing of the physiological cycle of the rhodopsin during the eye dark adaption process. The limits of the application of the method are discussed. This method is suitable for bright stars as Betelgeuse, Antares or Delta Scorpii or stars at the limiting magnitude observed with a telescope.

astro-ph.IM↗

arXiv2011

Occultazione asteroidale di 474 Prudentia su HIP 1927 con pre-pointing

An asteroidal occultation of a 8.5 V magnitude star can be difficult to be observed without an automatic pointing system. It was the case of 474 Prudentia occulting HIP 1927 on 5 September 2010, observed from the center of Rome. The solution of pre-pointing the telescope to Jupiter and leaving it fixed for 20 m 30 s, allowed to have the correct field of view and to observe successfully the phenomenon. This was possible because Jupiter was at the same declination of the target star, and 20m30s of right ascension to the west of it. With opportune modifications this method can be applied in similar cases, when the observing equipment is minimal. In that case, for example, many observers could have been witness of such an event, helping to recover the shadow path across the city.

astro-ph.EP↗

arXiv2011

Moti e distanze angolari in cielo con telescopio e cronometro

A basic telescope and a chronometer can be used to learn classical methods of spherical astronomy. The conjunction Venus-Saturn of July 2, 2007 has been observed through July 3 with a 50 mm telescope. Planetary daily motions and angular distances with respect to Psi Leonis, have been obtained with telescope field of view crossing times with an accuracy of 1 arcminute. In the age of CCD astronomy and planetarium programs for personal computer available to everyone, those are educational occasions to approach 3-D astronomy from real data, self obtained.

astro-ph.IM↗

arXiv2011

Astronomy in the Church: the Clementine Sundial in Santa Maria degli Angeli, Rome

Pope Clement XI (1700-1721) ordered Francesco Bianchini (1662-1729) to build a Meridian Line. Bianchini was the Secretary of the Commission for the Calendar. He chose the Basilica of Santa Maria degli Angeli because of the stability of its roman walls and foundations and its suitable dimension. Stability over centuries of the ancient walls where the pinhole is located is a requirement for making high precision astrometry, such as the measurement of the inclination of the Earth axis over its orbit plan. In the 18th century it was possible to open the window holding the southern pinhole, and, even in daylight, stellar transits were recorded and precisely timed with pendulum mechanical clocks. The accuracy of such clocks was better than 1 s per day, and the observations of stellar transits allowed their synchronization with sidereal time. This "hybrid feature" of the Clementine Gnomon to measure solar and stellar transits allowed Bianchini to accomplish in 1703 the whole measurement of the duration of the tropical year, which was usually made by comparing observations very widely spread in time. The small deviation of the Line from true North of ~ 4'30" Eastwards has been measured comparing the delays of transits at both solstices with respect to the ephemerides.

astro-ph.IM↗

arXiv2011

Measuring solar disk shape up to relativistic accuracy: the role of scintillation in ancient naked eye data

The orbital displacement of the Moon is known to a precision on the order of centimeters from the lunar laser ranging data, while the lunar profile's confidence level is still only about 200 m. The lunar motion is used to measure the solar diameter during central eclipses with accurate timing of Baily's beads at the umbral path limits. The onset or disappearance of a Baily's bead is due to the alignment between lunar limb's valleys and solar photosphere: this timing is determined outside our atmosphere. Due to scintillation, naked eye evaluations of such phenomena can be systematically different with respect to telescopes. We analyze the case of Venus' occultations as bead-like situation, in order to infer considerations on naked eye reports in historical total eclipse reports.

astro-ph.SR↗

arXiv2011

L'Epistolario di Gerberto, papa astronomo

A new Italian edition of the Letters of Gerbert, the astronomer, scientist and philosopher who become pope Silvester II, with their papal privileges has been published in the occasion of the international year of astronomy. The italian translation (1980) of Maria Giulia Panvini Carciotto (1949-1996), has been co-edited by Costantino Sigismondi and Paolo Rossi. The volume, according to the will of the relatives of Dr. Panvini Carciotto is available either in press and as free e-book on the web indexed with the words "Gerberto Episolario".

physics.hist-ph↗

arXiv2011

Incontri celesti, vita del padre Clavio in cinque atti

The year 2012 will be the fourth centennial year of the Jesuit Christopher Clavius (1535-1612), known as the Euclid of XVI century and the collaborator of the Pope Gregory XIII for the calendar reformation. In the occasion of the year of astronomy I wrote a short theatre pièce "Celestial encounters" dedicated to the life of Ft. Clavius. He observed two total eclipses from centreline in 1560 in Coimbra and in 1567 in Rome, a fact which is remarkable even for contemporary astronomers. The story is developed around those trips: scientific and religious motivations are put in evidence with historical and fantasy, but realistic, facts. An interregional project between Switzerland and Italy, dedicated to the development of high resolution CMOS camera for astronomy and medical sciences has been entitled to Clavius and will produce high resolution measurements of solar diameter.

physics.hist-ph↗

arXiv2011

Misure quantitative del seeing atmosferico

A simple technique of measurement of seeing in daytime and nighttime, based upon drift-scan observations, is presented, along with observational examples. This experience can be repeated easily in classroom contexts.

astro-ph.IM↗

arXiv2011

Ground-based measurements of solar diameter

The solar diameter changes or not? Whatever will be the answer the methods used for its measurements are more and more challenging, and facing new astrophysical and optical problems since the required space resolution is of astrometric quality. A quick overview on different methods is here presented, as well as the problem of the solar limb definition, emerging after the flash spectrum during eclipses.

astro-ph.SR↗

arXiv2011

Daytime Seeing and Solar Limb Positions

A method to measure the seeing from video made during drift-scan solar transits is proposed. The limb of the Sun is projected over a regular grid evenly spaced. The temporal dispersion of the time intervals among the contacts between solar limb and grid's rows is proportional to the atmospheric seeing. Seeing effects on the position of the inflexion point of the limb's luminosity profile are calculated numerically with Fast Fourier Transform. Observational examples from Locarno and Paris Observatories are presented to show the asymmetric contributions of the seeing at the beginning and the end of each drift-scan transit.

astro-ph.IM↗

arXiv2011

Towards a unified definition of solar limb during central eclipses and daily transits

The diameter of the Sun has been measured using Baily's beads during central eclipses, observed with portable telescopes. A blend of tiny emission lines produced in the first several hundred kilometers above the photosphere gives a light signal which prolonges the light curves of the beads. The simple criterion of light OFF/ON adopted in the previous approaches to define the timing of photosphere's disappearance/reappearance is modified. The technique of the limb darkening function reconstruction from the Baily's beads light curves is introduced here.

astro-ph.SR↗

arXiv2011

Relativistic implications of solar astrometry

The modern methods of measurement of the solar diameter and oblateness are reviewed. Either ground-based or balloon-borne and satellite measurements are considered. The importance of solar astrometry for General Relativity is emphasized, particularly attention is given to the solar oblateness problem, as well as the studies of solar astrophysics to the whole world of physics from nucleosynthesis to neutrinos.

astro-ph.SR↗

arXiv2011

Sunsets and solar diameter measurement

A sunset over the sea surface offers the possibility to chronometrate a solar transit across the horizon. The vertical solar diameter is proportional to the duration of the sunset, the cosine of the azimuth and the cosine of the latitude of the observing site. The same formula applies to every circle of equal height, called in arabic almucantarat, and it is exploited in the measurements of the solar diameter made with the Danjon's solar astrolabes. The analogies between sunsets and astrolabes observations are presented, showing advantages and sources of errors of these methods of solar astrometry.

astro-ph.IM↗