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 Sigismondisigismondi@icra.it

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!