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We are 66 Km North of the Tropic of Cancer…

We are 66 Km North of the Tropic of Cancer…. Eratostenes’ method for measuring Solar Diameter. ~ 272-192 b.C. Method quoted by Posidonius (135 - 51 b. C.), master of Cicero. Measures of Solar Diameter with Eclipses. Costantino Sigismondi sigismondi@icra.it Lights of the Dark Universe

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We are 66 Km North of the Tropic of Cancer…

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  1. We are 66 Km North ofthe Tropic of Cancer…

  2. Eratostenes’ method for measuring Solar Diameter ~272-192 b.C.

  3. Method quoted by Posidonius (135 - 51 b. C.), master of Cicero

  4. Measures of Solar Diameter with Eclipses Costantino Sigismondi sigismondi@icra.it Lights of the Dark Universe HuaLien, May 31, 2008

  5. A project in collaboration with • PICARD team (France) • SDS team (Yale - NASA) • IOTA (D. W. Dunham, W. H. Warren) Started at Rome Astronomical Observatory Goals: Sampling 500 years of solar diameter history Calibration for ground based measurements

  6. 60 years series of solar diameters by transits at Campidoglio since 1877 e.g. T. Fortini, MemSAIt 20 327 (1949)

  7. On the medieval tower of Pope Boniface IX (1389)

  8. This observatory no more exists

  9. Solar Tradition in Rome: from Father Angelo Secchi (1818-78)

  10. Eclissi e Diametro

  11. Duration vs distance from centerline: maximum variation near shadow’s limits

  12. Orbital motions are precisely known • JPL ephemerides • IMCCE french ephem. (Planets, Sun and Moon) e.g. Mercury’orbit analytical model < 4 mas + • Lunar Laser Ranging 2 cm accuracy (Fienga et al 2003) http://www.iers.org/documents/publications/tn/tn29/tn29_093.pdf

  13. Lunar Limb: profiles accuracy • Chester Watts (1962) published the atlas of lunar limbs at all libration phases

  14. Digitized Watts Atlas Available in Winoccult freeware program, by D. Herald

  15. Updated with stellar occultations Maximum uncertainty on a single feature: ±200 mas

  16. Chang’e-1: Lunar mission in progress Launched on October 24, 2007: Lunar Mapping will finally update limb’s profiles up to 0.001” accuracy?

  17. Baily’s Beads (discovery 1842) • Lunar limb cuts portions of solar photosphere • Timing and locating their dis/appearances yields N points of solar disk with ± 200 mas each (systematic, reduced with polar beads observations) • Final Statistical Uncertainty on Solar Diameter ~1/√N ranging from 50 mas (N=16), to 30 mas (N=50)

  18. Observational strategy • Getting the maximum number/duration of Baily Beads with • Geographical location • UTC timing • Going to grazing eclipses(polar beads)

  19. Caribbean Eclipse 1998 • Bead’s Identification (PA+time)

  20. Geographical location • Referred to permanent landscape features • GPS / Satellite image

  21. UTC timing • Has to be precise (0.01 s) • Has to portable • Has to be temperature calibrated

  22. Typical Time errors for Quartz watches

  23. Calibration with video recording Radio Signals • Of internal quartz watch of CamCorder • Of auxiliary quartz watch

  24. Imaging the eclipse • Naked eye (1567-1715-1925) • Video + high density filters • Video + projection

  25. Signal to Noise ratio To determine the faintest beador its limiting magnitude

  26. Sky background • If the projection is not made in a camera obscura there are different background levels, ranging over more than 1000 in intensity Total eclipse, Egypt Zawyet al Mahtallah march 29, 2006 Southern Limit

  27. Annular eclipse 92.5% • Kourou, French Guyana Sept. 22, 2006, Sun at 8° above horizon

  28. Sunset /Sunrise • Ostia (Rome, Italy) Sept. 5, 2006

  29. High Clouds • Roma, Oct. 18, 2006

  30. Atmospheric extinction Explained by a thin plane parallel layer of humidity Deviation starts at ~4° above horizon

  31. Solar Limb Darkening Function From Rogerson, 1959

  32. Intensity rises from 16% to 33% within 2.5 arcsec from limb

  33. Our equipment + + White Projection Screen + Camcorder and 2 quartz calibrated watches

  34. Our Measurements • Spain, 2005 (clouded; data from other observers; our idea was to measure the same eclipse with different devices)

  35. Egypt, 2006: more than 50 beads identified; ∆R= -0.17”±0.24”

  36. Corona at the shadow limit Before totality (± 4 minutes of visibility at naked eye)

  37. At maximum eclipse At naked eye the irregular structure of the corona was well visible. Does exists a Circular Inner Corona?

  38. Stephenson et al, 1997 say “YES”and consider total the eclipse of Rome,1567 observed by Clavius

  39. Clavius wrote a Commentarius to the Sphaera of Sacrobosco (John Holywood, Sphaera -1256)

  40. In 1581 edition Clavius wrote: relinquebatur in Sole circulus quidam exilis undique totam lunam ambiens. He actually saw an annular eclipse. The Sun in 1567 was >2.5 arcsec larger than now ? Not possible for physical reasons…

  41. Clavius was the teacher of Father Matteo Ricci from 1572 to 1578

  42. Astron. Astrophys 1997, the debate continues

  43. Halley and Royal Society: Eclipse of May 3, 1715

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