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)
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
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)
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
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
Atmospheric extinction
Deviation starts at ~4° above horizon
Explained by a thin plane parallel layer of humidity
Our Measurements
• Spain, 2005 (clouded; data from other observers; our idea was to measure the same eclipse with different devices)
At maximum eclipse
At naked eye the irregular structure of the corona was well visible.
Does exists a Circular Inner Corona?
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
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…
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...
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
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