we are 66 km north of the tropic of cancer…
DESCRIPTION
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 [email protected] Lights of the Dark Universe - PowerPoint PPT PresentationTRANSCRIPT
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We are 66 Km North ofthe Tropic of Cancer…
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Eratostenes’ method for measuring Solar Diameter
~272-192 b.C.
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Method quoted by Posidonius (135 - 51 b. C.), master of Cicero
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Measures of Solar Diameter with Eclipses
Costantino [email protected]
Lights of the Dark UniverseHuaLien, May 31, 2008
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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 historyCalibration for ground based measurements
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60 years series of solar diameters by transits at
Campidoglio since 1877
e.g. T. Fortini, MemSAIt 20 327 (1949)
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On the medieval tower of Pope Boniface IX (1389)
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This observatory no more exists
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Solar Tradition in Rome: from Father Angelo Secchi (1818-78)
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Eclissi e Diametro
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Duration vs distance from centerline: maximum variation
near shadow’s limits
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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
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Lunar Limb: profiles accuracy
• Chester Watts (1962) published the atlas of lunar limbs at all libration phases
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Digitized Watts Atlas
Available in Winoccult freeware program, by D. Herald
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Updated with stellar occultations
Maximum uncertainty on a single feature: ±200 mas
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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?
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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)
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Observational strategy
• Getting the maximum number/duration of Baily Beads with
• Geographical location
• UTC timing
• Going to grazing eclipses(polar beads)
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Caribbean Eclipse 1998•Bead’s Identification (PA+time)
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Geographical location• Referred to permanent landscape
features• GPS /
Satellite image
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UTC timing
• Has to be precise (0.01 s)
• Has to portable • Has to be
temperature calibrated
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Typical Time errors for Quartz watches
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Calibration with video recording Radio Signals
• Of internal quartz watch of CamCorder• Of auxiliary quartz watch
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Imaging the eclipse
• Naked eye (1567-1715-1925)
• Video + high density filters
• Video + projection
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Signal to Noise ratio
To determine the faintest beador its limiting magnitude
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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
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Annular eclipse 92.5%
• Kourou, French Guyana Sept. 22, 2006, Sun at 8° above horizon
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Sunset /Sunrise
• Ostia (Rome, Italy) Sept. 5, 2006
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High Clouds
• Roma, Oct. 18, 2006
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Atmospheric extinction
Deviation starts at ~4° above horizon
Explained by a thin plane parallel layer of humidity
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Solar Limb Darkening Function
From Rogerson, 1959
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Intensity rises from 16% to 33% within 2.5 arcsec from limb
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Our equipment
+
+White Projection Screen
+ Camcorder and 2 quartz calibrated watches
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Our Measurements
• Spain, 2005 (clouded; data from other observers; our idea was to measure the same eclipse with different devices)
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Egypt, 2006: more than 50 beads identified; ∆R= -0.17”±0.24”
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Corona at the shadow limit
Before totality (± 4 minutes of visibility at naked eye)
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At maximum eclipse
At naked eye the irregular structure of the corona was well visible.
Does exists a Circular Inner Corona?
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Stephenson et al, 1997 say “YES”and consider total the eclipse of Rome,1567 observed by Clavius
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Clavius wrote a Commentarius to the Sphaera of Sacrobosco
(John Holywood, Sphaera -1256)
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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…
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Clavius was Clavius was the teacher the teacher of Father of Father
Matteo Ricci Matteo Ricci from 1572 to from 1572 to
15781578
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Astron. Astrophys 1997, the debate continues
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Halley and Royal Society: Eclipse of May 3, 1715
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Philosophical Transactions 1717
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Prof. Brown (Yale) for NYC eclipse1925
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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…
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from Fiala, Dunham & Sofia, So. Phys. 152, 92 (1994)
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Climate ChangesFrom John L. Daly www; K. Schatten www
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Solar Activity
• From Usokin and KavaltsovSo. Phys. 224, 37 (2004)
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Anticorrelation radius-sunspots?from Sofia et al. 2006, not based on eclipses
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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...
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And Transits?• Venus 1769: Discovery of Black Drop effect
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1882 Transit: with photographs
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Explanation of Black dropG. Horn d’Arturo – J. Pasachoff (TRACE)
due to instrumental optical distortions
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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
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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)
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Solar Diameter measurement
• With only 50 images• Internal contacts:• 2nd @ 7 am ± 8 s (low Sun, high
atmospheric turbulence)• 3rd @ 1 pm ± 1 s• Application to solar diameter with D.
Herald’s Winoccult software (Sigismondi, 2006):
• ΔR=0.69±0.38 arcseconds
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November 8, 2006Mercury transit
At the R. B. Dunn Telescope at Sacramento Peak sunset occurred before 3 contact;
Mauna Kea too windy for 1st contact
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2008, august 1 ?
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Help is welcome!