Cape and Paris meridian observations of the solar limbs which permit an estimate to be made of the solar semi-diameter were surveyed, sampled, and compared with Greenwich and U.S. Naval Observatory observations. Significant systematic errors were found in the Paris work and have been correlated with changes of instruments and observers. Results from the Cape series indicate that work should continue on the compilation of data from Cape observations of the Sun

Messina, D.

Smith, C.

English

NASA Technical Reports Server

N82' 17024
PRECEDINGPAGEBLANKNOTFILMED
THE HORIZONTAL AND VERTICAL SEMI-DIAMETE,RS OF THE SUN OBSERVED AT
THE CAPE OF GOOD HOPE (1834-1887) AND PARIS (1837-1906): A REPORT ON WORK
IN PROGRESS
Clayton Smith and Dan Hessina _
O.S. Naval Observatory
ABSTRACT
Cape and Paris meridian observations of the solar limbs which permit
an estimate to be made of the solar semi-diameter are being surveyed,
sampled, and compared with Greenwich and U.S. Naval Observatory observa-
tions. Significant systematic errors have been found in the Paris work
and have been correlated with changes of instruments and observers. It is
unlikely that further work on the Paris series would shed light on the
problem of changes in the solar semi-diameter. Preliminary results from
the more stable Cape series indicate that work should continue on the
compilation of data from Cape observations of the sun.
INTRODUCTION
The possibility of a secular decrease in the apparent solar semi-
diameter (referred to standard co._ditions) has been suggested from studies
of meridian circle observations made at the Royal Greenwich and the U.S.
Naval Observatories (refs. 1,2,3). Two other serles of observations not
previously discussed are available from the Royal Observatory at the Cape
of Good Hope (Cape) In South Africa from 1834 to 1887 (ref. 4) and at the
Paris Observatory (Paris) from 1837 co 1906 (ref. 5). The Cape series is
of particular interest because of the Cape's southern hemisphere location.
The Paris series is of interest because of the 70 year tlme-span.
A method for reducing raw observations to standard conditions is
given, the method was applied to selected subsets of the original mass of
observational material, and the results are discussed.
DATA _ALYSIS
Solar observations were reduced as follows (ref. 6):
15RAacos_ (1)SDH = 2S '
where SDH = horizontal semi-diameter at unit distance (one A.U.),
R = earth-sun distance in units of A.U. at the time of observation,
* NASA Contract PCN 961-72273(IC)
¢ University of Maryland
III
1982009140-111
https://ntrs.nasa.gov/search.jsp?R=19820009150 2020-03-21T10:57:40+00:00Z
J
!
8u = measured difference in time between the east and west limbs,
S - a correction factor for the sun's motion in right ascension during
the time between meridian passage of the east and west limbs.
• S = i/(i-_aS/3609.86), where Aas is the rate of change in right
ascension of the sun in units of seconds of time per mean solar
hour. (See table I for the monthly value used in any year.), and
- sun's apparent observed declination.
In some cases the north polar distance (NPD) was given, rather than the
declination. In those cases, sin(NPD) was substituted for cos6.
In the other coordinate:
R_
SDV = _ , (2)
where SDV - vertical semi-diameter at unit distance (one A.U.), and
86 = measured difference between north and south llmb declinations
corrected for refraction.
Our strategy was to survey several years at the beginning and end
of an instrumental series. Annual averages of S_{ and SDV have been com-
puted for Cape for the years 1834, 1884-1887, and 1861-1865 and are st_-
marlzed in table II. Annual averages of SDH and SD V from Paris for the
years 1837-1841, 1859-1867, and 1885-1890 are summarized in table IIl.
The entire Cape series was observed with no significant change in
instrumentation or observers. However, the Paris series is composed of
subsets of observations with four diffent instruments as indicated in
table Ill. Si_nlflcant changes in the observing staff from one year to
the next were also noted.
PRELIMINARY RESULTS
CAPE
A test of the Cape results SDH and SDV of table II for a linear rate
with time, T, by means of a least squares fit yielded the solutions
d(SDH)/dT = -0.6 ± 0.6 seconds of arc per century and d(SDv)/dT = -0.4 ± 0.4
seconds of arc per century, from 1834 to 1887, and 1861 to 1887, resp. From a
statistical point of view, these results can barely be regarded as signifi-
cant. However, since the mean errors are of the same order of magnitude as
the rates and not very much larger, and since the two independent solutions
are in better agreement with each other than expected from their relative
errors, there is some indication that a nlearer picture may emerge if the
survey of Cape sun observations Is broadened to include data from the ti_e
interval 1865 to 1884, 8nd close attention is paid to the change in the mix
of observers from one year to the hext.
This preliminary result may be compared with the results of_IJ Eddy _md
Boornazlan (refs. 2,3) who found a secular decrease of -2" per century in
112
1982009140-112
I"
SDH and -0"8 per cen_.ury In SDV from Greenwich and U,,S. Naval Observatory
meridian observatlons;(2) I. _haplro (ref. 7) who from transits of Mercury
found that any decrease in the solar diameter Is llkely to be under 0';3 per
century;(3) D. Dunbar, et al. (ref. 8) who found from an analysis of solar
ecllpses that the solar radius has contracted 0.34 -+ 0.2 seconds of arc in
264 years; and(4) A. Wittman (ref. 9) who from the agreement bet__:n the
mean of Tobias Mayer's observations of the sun, 1756-1760, and recent photo-
electrlc results obtained in the 1970's finds no support for a secular
decrease in the solar radius.
PARIS
The Paris results are inconclusive. Larg,_ systema._Ic differences of the
personal equation of individual observers having an effect as large as two
seconds of arc on the determination of SDH have been dc__umented, and explain
the discordant values of SDH for 1866,1867, and 1902-1906. On the other hand,
the signlficant decrease of SDH from the 1840's to the 1860's is consonant
within their relative errors wlth a slnLilar decrease in the Greet-with
results. -
There Is no significant change in the Paris SDV of the 1837-1841 period
compared with the 1859-1863 period, which is noc in agreement with the Green-
wich results over the same interval of t1.,T,. Since different instruments
were used at Paris in the 1837-18&i and 18 9-1863 periods, i.e., the Fortln
Mural Circle was used in the first period and the Gambey Mural Circle was
used In the second perJod, systematic instrumental effects probably are at
the root of the disagreement between Paris and Greenwich over that interval
of tin_.
It was very disturbing to find that for the subset of observations
made wlth the Crande Instr,,,ent Merldlenne from 1863 to 1906 for which we
have values of SDv, the values were systematlcally larger than the _arlier
Paris values by about 1.5 seconds of arc, and also systematically larger than
the Gree:tw_ch SDV by about the same amcunt in the interval i_63 to 1906. This
abrupt change in the system was probably caused by an instrumental change
rather than an observer change. We have been able to document that changes of
obr.erver from one year to the next which grossly affect the SDH (compare SDH
,;alues 1885-1889 to SDH values 1902-1906) cause no sisnlf%cant change in the
correspondlng SDV values observed with the same instrument.
FUTURE WORK
Our next efforts viii focus on completing the,dlscusslon of the Cape ob-
servatlons and then turning to the lonR series of the O.S. Naval Observatory.
We hope to use concurrent Nav_l Observa¢ory observation-: of the limbs of Ju-
piter and Saturn to indicate how dl_ter measure_nts can be affectsd sys-
tematlcally by personal equation and changes tn instrumentation apart from
ch,_nges which may occur as the resul," of severe punishment o" the instrmln-
ration durlns solar observations.
I13
1982009140-113
]?
REFERENCES
i. Gething, P.J.D.: Greenwich Observations of the Horizontal and Vertical
Diameters of the Sun. Mon. Not. Roy. Ast. Soc., vol. 115, no. 5, 1955,
pp. 558- 570.
2. Eddy, J.A. and Boornazian, A.A. : Secular Decrease in the Solar Diameter.
Ball. of the Amer. Ast. Soc., vol. 11, no. 2, ]979, p. 437.
3. Lubkin, G.B.: Analyses of Historical Data Suggest Sun is Shrinking.
Physics Today, vol. 32, no. 9, Sept. 1979, pp. 17-19.
4. Royal Observatory, Cape of Good Hope, South Africa. Annual volumes of
meridian observations 1834-1877.
5. Paris Obsercatory Annals. Annual volumes 1837-1906.
6. Explanatory Supplement to the Astronomical Ephemeris and the American
Ephemeris and Nautical Almanac., London. Her Majesty's Stationery.
Office., 1961, pp. 137-141.
7. Shapiro, I.: Is the Sun Shrinking? Science, vol. 208, no. 4, April 1980,
pp. 51-53.
8. Dunham, D.W.; Sofia, S.; Fiala, A.; Herald, D.; Muller, P.M.: Observa-
tions of a Probable Change in the Solar Radius Between 1715 and 1979.
Science, vol. 210, no. 12, Dec. 1980, pp. 1243-1245.
9. Wittman, A.: Tobias Mayer's Observations of the Sun: Evidence Against A
Secular Decrease of the Solar Diameter. Solar Physics, vol. 66, 1980,
pp. 223-231.
114
1982009140-114
!TABLE I. S, A CORRECTION FACTOR FOR THE MOTION OF I_IE SUN
l
[
Jan. 1.00297 July 1.00281 i
Feb. 1.00271 Aug. 1.00259 f
Mar. 1.00253 Sept. 1.00249 i_
Apr. 1.00256 Oct. 1.00258
May 1.00274 Nov. 1.00284 i
June 1.00288 Dec. 1.00307 !
TABLE II. ANNUAL MEANg OF SOLAR SEMI-DIAMETERS FROM OBSERVATIONS AT CAPE
Year SDH No. of Obsns. SDV No. of Obsns. i
1834 961_50 132 -- 0
1861 961.25 61 962_35 37
1862 960.63 37 962.04 32
1863 961.19 42 962.43 33
1864 961.57 54 962.29 53
1865 961.50 68 962.13 65
1884 960.86 69 962.09 77
1885 961.16 19 962.17 19
1886 961.34 141 962.27 150
1887 961.09 175 962.09 179
115
1982009140-115
LTABLE III. ANNUAL MEANS OF SOLAR SEMI-DIAMETERS FROM OBSERVATIONS AT PARIS
Year SDH No. of Obsns. SDV No. of Obsns.
1,unette Merldienne de Gambey(gMG) Fortln Mural Circle
1837 962U24 146 960_56 20
1838 962.62 iii 960.70 4
1839 962.26 121 -- 0
1840 962.75 142 961.35 Ii •
1841 962.03 93 960.92 17
LMG (continued) Gambey Mural Circle
1859 961.90 136 -- 0
1860 961.20 77 961.28 3
1861 961.55 108 960.49 4
1862 960.67 42 961.56 8
1863 960.57 58 961.25 36
Grande Instrument Meridienne (in both coordinates)
1863 961.19 25 963.18 20
1864 961.54 102 962.45 141
1865 960.62 i01 961.71 9B
1866 962.68 54 962.67 45
1867 962.03 76 962.50 73
1885 961.20 114 962.39 96
1886 961.25 126 962.44 119
1887 961.68 92 962.56 90
1888 961.29 93 962.45 57
1889 961.48 173 962.54 79
1902 962.85 105 962.42 93
1903 962.87 93 962.29 92
1904 962.80 97 962.49 89
1905 962.92 88 962.52 82
1906 963.05 88 962.54 87
I16
1982009140-116


The horizontal and vertical semi-diameters of the Sun observed at the Cape of Good Hope (1834 - 1887) and Paris (1837 - 1906):  A report on work in progress

The horizontal and vertical semi-diameters of the Sun observed at the Cape of Good Hope (1834 - 1887) and Paris (1837 - 1906): A report on work in progress

Abstract

Similar works

Full text

Available Versions

NASA Technical Reports Server