# The Greenwich Photo-heliographic Results (1874 – 1976): Procedures for Checking and Correcting the Sunspot Digital Datasets

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## Abstract

Attention is drawn to the existence of errors in the original digital dataset containing sunspot data extracted from certain sections of the printed *Greenwich Photo-heliographic Results* (*GPR*) *1874 – 1976*. Calculating the polar coordinates from the heliographic coordinates and comparing them with the recorded polar coordinates reveals that there are both isolated and systematic errors in the original sunspot digital dataset, particularly during the early years (1874 – 1914). It should be noted that most of these errors are present in the compiled sunspot digital dataset and not in the original printed copies of the *Greenwich Photo-heliographic Results*. Surprisingly, many of the errors in the digitised positions of sunspot groups are apparently in the measured polar coordinates, not the derived heliographic coordinates. The mathematical equations that are used to convert between heliographic and polar coordinate systems are formulated and then used to calculate revised (digitised) polar coordinates for sunspot groups, on the assumption that the heliographic coordinates of every sunspot group are correct. The additional complication of requiring accurate solar ephemerides in order to solve the mathematical equations is discussed in detail. It is shown that the isolated and systematic errors, which are prevalent in the sunspot digital dataset during the early years, disappear if revised polar coordinates are used instead. A comprehensive procedure for checking the original sunspot digital dataset is formulated in an Appendix.

### Keywords

Greenwich photo-heliographic results Positions and areas of sunspots and faculae Reconstructed solar images Isolated and systematic errors Mathematical equations Solar ephemerides Preliminary corrections Generalised checking procedures## Notes

### Acknowledgements

The authors thank J.H. Allen, L. Győri, R.A. Harrison, F.R. Stephenson, and P.T. Wallace for much valuable advice, assistance and encouragement during the preparation of this paper. They are also greatly indebted to a referee for suggesting substantial improvements to the presentation of the material included in the paper.

### References

- Carrington, R.C.: 1863,
*Observations of the Spots on the Sun from November 9, 1853 to March 24, 1861, Made at Redhill*, Williams and Norgate, London. Google Scholar - De La Rue, W., Stewart, B., Loewy, B.: 1869, Researches on solar physics: heliographical positions and areas of sun-spots observed with the Kew photoheliograph during the years 1862 and 1863.
*Phil. Trans.***159**, 1 – 110. CrossRefGoogle Scholar - Dezső, L., Gerlei, O., Kovács, Á.: 1987,
*Debrecen Photoheliographic Results for the Year 1977*, Heliophysical Observatory of the Hungarian Academy of Sciences, Debrecen. Google Scholar - Erwin, E.H., Coffey, H.E., Denig, W.F., Willis, D.M., Henwood, R., Wild, M.N.: 2013, The Greenwich Photo-heliographic Results (1874 – 1976): initial corrections to the printed publications.
*Solar Phys.*doi: 10.1007/s11207-013-0310-z. Google Scholar - Győri, L.: 1989, Problems in determining heliographic coordinates, Doctoral Thesis, Kossuth Lajos University, Debrecen, Hungary (in Hungarian). Google Scholar
- JPL: 2005, JPL Horizons On-Line Ephemeris System. http://ssd.jpl.nasa.gov/?horizons.
- Meeus, J.H.: 1991,
*Astronomical Algorithms*, Willmann-Bell, Richmond (2nd edn. 1998). Google Scholar - Royal Greenwich Observatory: 1975,
*Royal Observatory Annals Number 11*(Photoheliographic Results 1967, Royal Greenwich Observatory, Herstmonceux), Science Research Council, Sumfield and Day Limited, Eastbourne, East Sussex. Google Scholar - Seidelmann, P.K. (ed.): 1992,
*Explanatory Supplement to the Astronomical Almanac: a Revision to the Explanatory Supplement to the Astronomical Ephemeris and the American Ephemeris and Nautical Almanac*, University Science Books, Mill Valley. Google Scholar - Willis, D.M., Davda, V.N., Stephenson, F.R.: 1996, Comparison between oriental and occidental sunspot observations.
*Q. J. Roy. Astron. Soc.***37**, 189 – 229. ADSGoogle Scholar - Willis, D.M., Coffey, H.E., Henwood, R., Erwin, E.H., Hoyt, D.V., Wild, M.N., Denig, W.F.: 2013, The Greenwich Photo-heliographic Results (1874 – 1976): summary of the observations, applications, datasets, definitions and errors.
*Solar Phys.*doi: 10.1007/s11207-013-0311-y. Google Scholar