1. We are 66 Km North of the 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

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

11. Eclissi e Diametro

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

13. 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

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

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

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

17. 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?

18. 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)

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

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

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

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

23. Typical Time errors for Quartz watches

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

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

26. Signal to Noise ratio To determine the faintest bead or its limiting magnitude

27. 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

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

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

30. High Clouds Roma, Oct. 18, 2006

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

32. Solar Limb Darkening Function From Rogerson, 1959

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

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

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

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

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

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

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

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

45. 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…

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

48. Astron. Astrophys 1997, the debate continues

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

51. Philosophical Transactions 1717

52. Prof. Brown (Yale) for NYC eclipse 1925

53. Exeligmos: 54 years 33 days 1979 another total eclipse in USA with same libration phase ΔR= -0.6” from 1715 to 1979 with all variation in 1925-1979…

54. from Fiala, Dunham & Sofia, So. Phys. 152, 92 (1994)

55. Climate Changes From John L. Daly www; K. Schatten www

56. Solar Activity From Usokin and Kavaltsov So. Phys. 224, 37 (2004)

57. Anticorrelation radius-sunspots? from Sofia et al. 2006, not based on eclipses

58. French Guyana, Sept. 2006 Eclipse at sunrise, high extinction and bad seeing 16 beads identified ΔR= -0.01±0.17 arcsec: average value at solar minimum...

59. And Transits? Venus 1769: Discovery of Black Drop effect

60. 1882 Transit: with photographs

61. Explanation of Black drop G. Horn d’Arturo – J. Pasachoff (TRACE) due to instrumental optical distortions

62. Black drop affects the methods of measuring solar diameter Uncertainty of the contact timings up to several minutes… We avoid it in eclipses choising only dis/appearance of beads (light OFF/ON) which are optically independent For transits the ultimate obstacle is now atmospheric seeing

63. Transit of Venus 2004 Chord method Intersection between two chords: analytical Fit with 3 free parameters: in/egress constant velocity Venus diameter (maximum of red chord) In/egress time (output)

64. Solar Diameter measurement With only 50 images Internal contacts: 2 nd @ 7 am ± 8 s (low Sun, high atmospheric turbulence) 3 rd @ 1 pm ± 1 s Application to solar diameter with D. Herald’s Winoccult software (Sigismondi, 2006): ΔR=0.69±0.38 arcseconds

65. November 8, 2006 Mercury transit At the R. B. Dunn Telescope at Sacramento Peak sunset occurred before 3 contact; Mauna Kea too windy for 1 st contact

66. 2008, august 1 ?

67. Help is welcome!