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