The solar limb during eclipses:
Flash Spectrum Region and Baily beads
Costantino Sigismondi
ICRA-Sapienza, Roma; Université de Nice-Sophia Antipolis
and IRSOL Istituto Ricerche Solari di Locarno
[email protected]
post-éclipse meeting, IAP 30.9.2010
ICRA and solar physics
www.icra.it/solar
Participating institutions
ICRA, International Center for Relativistic Astrophysics
Sapienza University of Rome #
IOTA ES and US * #
Osservatorio Astronomico di Roma #
Basilica di Santa Maria degli Angeli, Roma *
Yale Astronomy Department #
Université de Nice-Fizeau Dept. #
Observatoire de la Cote d'Azur(Calern site PICARD Sol)*
Institute d'Astrophysique de Paris * #
IRSOL * #
# data and analysis * observations (CLAVIUS)

Classification of
Solar diameter measurements
Measuring radius from Earth
Drift-scan:
solar angular speed * transit time = diameter
problem: seeing
• Angular direct measurements
– problem: seeing, optical aberration
• Mercury and Venus transits:
planetary speed * transit time = diameter
- problem: scintillation, black drop
• Eclipses with Baily’s beads
– problem: scintillation, signal to noise, filter, FSR
Last solar cycle XXIII:
SOHO data (June 2010)
Calibrating eclipses for studying
secular variations
Eclipse Problem 1: scintillation
Problem 2: Flash Spectrum Region
Flash Spectrum (1905)
Problem 3: lunar profile
Watts (1962) σ>0.2” random
Kaguya (2009) σ<<0.01” sampling each 0.5”-5”
Sampling 1-10 km

Real lunar limb vs Watts profile
(Kilcic, Sigismondi, Rozelot &
Guhl, So. Phys. 2009)
Locarno Solar Obsevratory
IRSOL Istituto Ricerche
Solari di Locarno
10 km
δR=-0.41”±0.05 ” (Kilcic et al. 2009)
on 29 march 2006,
in agreement with SOHO 2003 data
preliminary:δR=-0.36”±0.15” on 15 Jan 2010,
based on 6 beads from R.Nugent
LIMB DARKENING FUNCTION WITH BAILY’S
BEADS ANALYSIS
Andrea Raponi and C. Sigismondi
Sapienza University of Rome
Total Solar Irradiance changed in the past, so also
the diameter?
Hendrick Avercamp (1585-1643), Amsterdam
Eclipses
Beads of 15/01/2010 by R. Nugent
with Kaguya profile; software Occult
Solar Limb and LDF
seeing and inflection point
Baily’s bead light
curve
depends on
scintillation
Valley’s profile
+ real LDF
LDF and Flash Spectrum
Region?
computing LDF from light curve
and Kaguya lunar profile
LDF from 2 different beads
x:units of 6 mas
Synthetic LDF
from Poissonian noise
2.50
2.00
CONTEGGI / PIXEL
1.50
1.00
0.50
0.00
0
-0.50
0.1
0.2
0.3
0.4
0.5
0.6
0.7
SECONDI D'ARCO DAL SOLE STANDARD
0.8
0.9
1
Notes: quartz oscillators physics
Thewlis Enc. Dictionary of Physics, Pergamon Press 1962 Quartz, the
preparation and use of, oscillators
Annular Eclipse of 22/9/2006 2 watches: SONY e CASIO
in French Guyana the temperature was
> 8 °C than in Rome
Roman tradition in solar diameter
….and in eclipses:
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…