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Angelo Secchi in 1865 was called to perform marine hydrology experiments to ascertain the transparency of the Thyrrenian sea off the coast of Civitavecchia. From April to June he worked on Immaculate Conception's vapor vessel of the pontifical fleet. The work of Secchi lead to modern marine hydrology and limnology and the disk of Secchi is a common measurement standard also nowadays. An experimental setup for studying the transmittance of the water is presented in view of a cubesat dedicated to monitor the variations of the solar photospheric diameter.

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Optical spectroscopy developped so much in XIX century that many results required the quantum physics to be fully explained from selection rules to quantum probability. Angelo Secchi designed or modified some instruments like the Hoffman prisms to reach a great resolution, namely better than 1 Angstrom around the Sodium D-Lines. Alessandro Cacciani, who worked in Monte Mario Observatory and Sapienza University of Rome, invented and developped the MOF Magneto-Optical Filter by tuning the magnetic field in a vaporized sodium cell. The MOF is being used in the two MOT telescopes in Anctartica, and has been used in US and EU telescope reaching an extraordinary velocity resolution in the dopplerograms of the Sun. Two inventors in comparison, at a century of temporal distance, with Mount Mario Observatory ideally inherited the Collegio Romano story, because had the Merz telescope of Secchi until the fire of July 15, 1958.

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The seeing in the roman sky from Secchi to present is discussed by analyzing the work of Secchi on the Orion Nebula and after 2000 observations contributing to AAVSO international database by SGQ, author of this paper. Secchi found the daily and seasonal variability of the turbulence and transparency of the night sky with his long experience at Collegio Romano Observatory during the years of gradual change from night illumination with candles to gas. Sigismondi and Vollmann observed since 2012 Betelgeuse, with a database of almost 500 observations in visual and 500 in V bands, they are compared with V-band observations made in Austria by VOL and instrumental. The departures, up to 0.7 magnitudes, appear only at star-rise or star-set, when scintillation is maximal. The comparison between Orion Nebula observed at Secchi time with Merz refractor and nowadays with same aperture newtonian telescope is presented.

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Every observatory has a sighting scope and a target to align down to an arcsecond the axis of a telescope. Secchi located at 1.39 Km from the Collegio Romano Observatory his target whose dimensions of 4x7 cm are a standard like for atmosphere, as the Secchi disks are for marine water. In Rio de Janeiro a similar mira (target) was setup to calibrate the reflecting heliometer in daylight, using also artificial stars made with a metal sphere. This talk will be presented in two parts: in room and on site, during a celebrating walk from Pincio to St. Ignatius churc in occasion of the bicentennial of the birth the evening of July 2nd 2018.

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Clement XI financed the great sundial of Santa Maria degli Angeli as the first act of his pontificate in 1700, and was completed in 1702. The age-old problem of solar equation found the most exact solution of its time in the monumental Roman gnomon, built by the astronomer Francesco Bianchini. Bianchini published the first scientific results in 1703. An analytical calculation method is shown here to know the eccentricity and the perigee argument. In 1711 Donato Creti's paintings were donated to the Pope himself, representing the astronomic observations to convince him to realize the observatory of the University of Bologna, which was promptly financed. We discuss the quality of the images represented by Creti, in relation to Jupiter and its red spot. On the Roman College he ascended Pius VII Chiaramonti, on the occasion of an eclipse in 1806, to the tower of the abbot Calandrelli who during the suppression of the Jesuits (1774-1814) had taken the reins of the Tower Observatory built by Cardinal Zelada on the façade the building of the Roman College built upon the will of Gregory XIII, the pope of the calendric reformation in 1582. Leo XII in 1829 established the construction of the Sapienza University Observatory, the University Studium Urbis was founded by Bonifacio VIII in 1306, on the Bonifacio IX tower at the Campidoglio. This observatory specialized in solar astrometry and produced useful data until 1937 when it was dismantled. Pius IX finally supported financially and interacted constantly with the Jesuit Angelo Secchi called to direct the observatory of the Roman College from 1851 until 1878 when he died, a few months before the pope. At the Collegio Romano Secchi he began the stellar catalogue for stellar colors, starting to distinguish the first spectral types in the world. He also studied the Sun in depth, and is fully recognized as the father of astrophysics. Pius IX visited the Campidoglio observatory, as a plaque recalls, and what remained of the Observatory of the Collegio Romano and the Campidoglio constituted the Monte Mario Astronomical Observatory under the direction of Armellini, until 1958 when a fire destroyed the telescope Merz di Secchi in the main dome of Monte Mario. Dead Armellini, Cimino continued his studies and completed the construction of the Solar Tower in 1961.

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An algorithm of the feast based upon solstices, equinoxes and number 40 has been reckoned from ancient feasts celebrated in Abruzzo and later christianized by the Catholic church. The origin of the 40 game cards (neapolitans, sicilians and placentines) is related to this calendric function. Father Secchi's birthday is a Roman Catholic sollemnity: St. Peter and Paul martyrdom (the feast includes the vigil, 28-29 june), and it is not obtained by this algorithm. Is it a certain date for the two Apostles, the columns of Christianity?

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An approach to Quantum Physics through spectroscopy, thanks to the wave-particle behavior of the photon,is possible with many diffraction experiments. Selection rules Helium and Coronium searches are also important. In General Relativity the interferometer of Michelson has been adapted to gravitational waves in LIGO/VIRGO (2015); it can be realized at school. The Solar figure, spherical within few parts in a million, was measured by Dicke to assess the possibility of a scalar-tensorial theory beyond Einstein and now is measured to understand the physics of solar secular variabiliy, so important for our climate (Sigismondi, 2012). General Relativity was important to the view of the World as much as Quantum Physics. With Einstein the Physical Cosmology was born, because the Universe's behavior was comprised as a consequence of the matter's distribution (Peebles, Priciples of Physical Cosmology, 1990). The Galileian idea of same physics on the Earth and across all Universe reached its maximum extent. The Cosmological Constant and later stationary Universe of Hoyle, Bondi and Gold, and finally Hawking and Hartle proposed a Universe, conceptually not different from Aristotle's one, while Lemaitre proposed an evolutionary Universe, finding the observational proofs. The hot big bang theory was confirmed by the Cosmic Background Radiation discovery (1965) even if Zeldovic (1962) theorized a cold one, based upon Fermi energy. The role of Cosmic Ether, object of the studies of Michelson and Morley, is now played by the Dark Energy, novel Cosmological Constant, and producing an accelerating Universe. Comparing the theories of expanding Universe, eternal Universe, oscillating Universe with the ancient ones, made by Aristotle and condemned by Etienne Tempier bishop of Paris in 1277, is also important. According to Pierre Duhem (Système du Monde, 1913-58), this act was the starting point of the modern science. The construction of the theory, moreover, is based upon some principles, and the speed of light in vacuum-the veritable "celeritas"- cannot be surpassed. The recent (2011) debate of OPERA results in Gran Sasso National Laboratories and CERN of Geneva can be studied in this optics. Provided this frame, there are plenty of motivations to know the essence of General Relativity and its contribution to the view of our World.

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The father of Italian geodesy is Francesco Bianchini (1662-1729) who built the meridian line in the Basilica of S. Maria degli Angeli in Rome with the purpose of measuring accurately the variation of the obliquity of Earth's orbit and the tropical year duration. He compared the observations of eclipses made in Rome and in Bononia, at the meridian line (1655) made by Giandomenico Cassini and found that the meridian of the Pontifical State was from Rome to Rimini. While Bianchini published many details of the meridian line in 1703, the presence of two decorations near the Summer solstice position has remained unexplained until 2018. Only one of them receives the image of the Sun nowadays and allows immediately to evaluate the secular shift of the solstice's position. The position of the red marble strip under this decoration is the materialization of the solstitial center of the solar image in 1702. For 1.5 centuries the signal was given by that meridian line, Secchi was able to automatize the procedure of the ball-drop, as in Greenwich observatory. A signal was spread to the city, through the fall of a sphere visible from far on top of the Flamsteed house,to give the instant of the local meridian transit. This was established in 1833 and automated in 1852 by Airy. Secchi realized a similar device upon the roof of St. Ignatius, where his Observatory was located. This ball-drop gave the signal to the cannon on Gianicolo hill. Nowadays the tradition of the cannon continues, without the intervention of astronomers. Secchi measured carefully the meridian of Rome, and paved the way to the modern geodesy and the fundamental meridian of Italy at 12° 27' 08" from Greenwich.

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Angelo Secchi, following the tradition started with father Christopher Clavius (1535-1612) who wrote a mathematical treatise (1581) on Gnomonics, realized sundials and quadrants. The equation of time determines the difference between the mean solar noon and the true one. Graphically it is represented with an analemma, drawn also in the sundials made by Secchi (e.g. the ones of Grottaferrata and Augusta). The relationship between the day of the year and the corresponding equation of time, from Ptolemy to Clavius, is presented, including some medieval cases. Computation methods of the equation of time based on linear interpolation of trigonometrical functions are simulated for some historical cases before Clavius. In the same years of Secchi, the parish priest Giuseppe Sarto (1835-1914), future pope Pius X, was making sundials in Veneto and later told a joke about the equation of time when he was Pope.

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Archaeoastronomy was already existant during the lifetime of Angelo Secchi, after Stonehenge, started to be interpreted in an astronomical context. A medieval poetic text Phoebi Claro, of the tenth century, is examined using the positional astronomy tools presented by Secchi. The determination of day of the year, of the dawn described in Phoebi Claro, is presented. The day so found is around 11 of November, at the end of the liturgical year, in the feast of St. Martin (40 days before winter solstice), the end of commercial year, just before the Advent in preparation to Christmas, the real Christian Sunrise.

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