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The Greenwich Photo-heliographic Results (1874 – 1976): Summary of the Observations, Applications, Datasets, Definitions and Errors

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Abstract

The measurements of sunspot positions and areas that were published initially by the Royal Observatory, Greenwich, and subsequently by the Royal Greenwich Observatory (RGO), as the Greenwich Photo-heliographic Results (GPR), 1874 – 1976, exist in both printed and digital forms. These printed and digital sunspot datasets have been archived in various libraries and data centres. Unfortunately, however, typographic, systematic and isolated errors can be found in the various datasets. The purpose of the present paper is to begin the task of identifying and correcting these errors. In particular, the intention is to provide in one foundational paper all the necessary background information on the original solar observations, their various applications in scientific research, the format of the different digital datasets, the necessary definitions of the quantities measured, and the initial identification of errors in both the printed publications and the digital datasets. Two companion papers address the question of specific identifiable errors; namely, typographic errors in the printed publications, and both isolated and systematic errors in the digital datasets. The existence of two independently prepared digital datasets, which both contain information on sunspot positions and areas, makes it possible to outline a preliminary strategy for the development of an even more accurate digital dataset. Further work is in progress to generate an extremely reliable sunspot digital dataset, based on the programme of solar observations supported for more than a century by the Royal Observatory, Greenwich, and the Royal Greenwich Observatory. This improved dataset should be of value in many future scientific investigations.

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Acknowledgements

The authors thank J.H. Allen, T. Baranyi, S. Foster, R.A. Harrison, P.D. Hingley (Deceased), S.F. James, S.A. Matthews, A.J. Perkins, F.R. Stephenson, J.M. Vaquero, C. Vincent, and F. Ward for much valuable advice, assistance and encouragement during the preparation of this paper. They are also greatly indebted to all those scientists and curators whose names are listed in Section B.5 of Appendix B. The authors are grateful to a referee for suggesting significant improvements to the presentation of the paper.

Author information

Authors and Affiliations

  1. Space Physics Division, Rutherford Appleton Laboratory, Harwell Science and Innovation Campus, Didcot, Oxfordshire, OX11 0QX, UK

    D. M. Willis

  2. Centre for Fusion, Space and Astrophysics, Department of Physics, University of Warwick, Coventry, CV4 7AL, UK

    D. M. Willis

  3. NOAA National Geophysical Data Center, 325 Broadway, Boulder, CO, 80305, USA

    H. E. Coffey, E. H. Erwin & W. F. Denig

  4. UK Solar System Data Centre, Rutherford Appleton Laboratory, Harwell Science and Innovation Campus, Didcot, Oxfordshire, OX11 0QX, UK

    R. Henwood & M. N. Wild

  5. 108 Buffalo Run Trail, Berkeley Springs, WV, 25411, USA

    D. V. Hoyt

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  1. D. M. Willis
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  2. H. E. Coffey
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  3. R. Henwood
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  4. E. H. Erwin
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  5. D. V. Hoyt
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Appendices

Appendix A: The Archival Collections of RGO Solar Plates and Contact Prints

1.1 A.1 Aim of the Appendix

The aim of this appendix is to provide brief details of the locations of the archival collections of the Royal Greenwich Observatory (RGO) Solar Plates and Contact Prints within the United Kingdom, and information on how they can be accessed.

1.2 A.2 Catalogues of the RGO Collections of Solar Plates and Contact Prints

The RGO collections of Solar Plates and Solar Plates Contact Prints, namely classes RGO.50 and RGO.51, respectively, in the numerical sequence of the archival class-marks, were housed on the RGO Herstmonceux Castle site until the move of the RGO to Cambridge in 1990; before the move both collections were catalogued. The glass plates were then moved to purpose-designed accommodation in the RGO Cambridge Building on Madingley Road, whilst the contact prints were accessioned into the main run of RGO Archives when the whole body of the archival collection was transferred to Cambridge University Library (CUL) during 1989 – 1990.

The two catalogues were retrospectively converted by CUL archival staff in May – June 2009 and made available over the Internet from the Library web-pages using the University of Cambridge archival catalogue server named Janus; RGO.50 at http://janus.lib.cam.ac.uk/bd/node.xsp?id=EAD%2FGBR%2F0180%2FRGO%2050 and RGO.51 at http://janus.lib.cam.ac.uk/bd/node.xsp?id=EAD%2FGBR%2F0180%2FRGO%2051 .

Today, the original paper contact prints (1874 – 1917) are available for study in the Department of Manuscripts Reading Room of Cambridge University Library – for advice on access contact Adam Perkins (ajp21@cam.ac.uk), Curator of Scientific Manuscripts, Cambridge University Library. Digital copies can be made from an original print if the print is in sufficiently good condition.

In 1998, the entire archive of RGO glass plates, including the original solar plates, was transferred to the Momart warehouse in east London. However, it is hoped to transfer this entire collection of RGO plates to the Bodleian Library, Oxford, in due course, in order to ensure proper curation and public access. At present, requests to access the RGO solar plates (1918 – 1976) should be addressed to Dr Colin Vincent (colin.vincent@stfc.ac.uk), Head of Astronomy, Programmes Directorate, Science and Technology Facilities Council.

The archive collection of RGO solar plates has been scanned by scientists at the Mullard Space Science Laboratory (MSSL), University College London, although the digital images have not yet been calibrated. There is currently no online link to this dataset and requests for further information about the digital images should be sent to Sarah Matthews (sarah.matthews@ucl.ac.uk).

1.3 A.3 Archive Material Stored in the UK Solar System Data Centre

The UKSSDC holds almost 20 000 images of the Sun as contact prints and over 9000 images on glass plates. The visible-light contact prints were acquired at some of the contributing solar observatories listed in Table 1 (including the Cape, Dehra Dun and Greenwich) and cover the time interval 1910 – 1936 (June). There is also a completely separate collection of glass plates that spans the time interval 1903 – 1942. Most of these plates are in K light, with a few in Hα light. An online catalogue provides information on the availability of the various types of image ( http://www.ukssdc.ac.uk/cgi-bin/wdcc1/secure/rog_image_availability.pl ) and requests for specific images should be sent to the UKSSDC (support@ukssdc.ac.uk).

Appendix B: Observatory Codes and Coordinates

2.1 B.1 Aim of the Appendix

The aim of this appendix is twofold. The first goal is to gather together all of the information on the observatory codes used to identify the locations at which the measured solar photographs were acquired. The second goal is to provide details of the bibliographic references used to determine the geographic coordinates and altitudes of all the contributing solar observatories.

2.2 B.2 Original Observatory Codes

As noted in Section 5, the RGO–S&FDD includes a single-letter observatory code to identify the source of each solar photograph. These codes are as follows: A= Melbourne (Me), Australia; C= Cape of Good Hope, South Africa; D= Dehra Dun, India; E= Ebro, Spain; F= Fraunhofer Institut, Germany; G= Greenwich, UK, and Herstmonceux, UK; H= Harvard College, USA; I= India (Dehra Dun); K= Kodaikanal, India; M= Mauritius; T= Mount Wilson (Mt. W, W, P), USA; W= Washington, USA; Y= Yerkes Observatory, USA. The codes in parentheses are those used in the RGO printed observations, bulletins and annals (RGO–POBA) It should be noted that the two separate codes (D, I) for Dehra Dun, India, have been retained in the sunspot and faculae digital dataset (RGO–S&FDD) because they both appear in the RGO–POBA; initially I was used but subsequently D was introduced to distinguish Dehra Dun from Kodaikanal (K), India. It should also be noted that the code T is used for the Mount Wilson Observatory in the RGO–S&FDD to distinguish this observatory from the US Naval Observatory, Washington (W). The code Y is used for the Yerkes Observatory.

2.3 B.3 New Observatory Codes

The single-letter observatory code defined in Section B.2, which is a minor modification of the original RGO observatory code (A = Me and T= Mt. W), applies exclusively to the interval 17 April 1874 – 31 December 1955. At present, the sunspot and faculae digital dataset (RGO–S&FDD) only extends up to the end of 1955, when publication of the faculae measurements ceased. In the interval 1956 – 1976, the printed RGO publications (RGO–POBA) use some of the defunct single-letter observatory codes again for other observatories (e.g., D is used for Debrecen, whereas this letter had been used previously for Dehra Dun). To overcome this difficulty, a new four-letter observatory code is defined in Table 1, together with the original observatory codes employed in the printed RGO publications. It is clear from Table 1 that some of the old single-letter observatory codes are ambiguous. The new unambiguous four-letter observatory code is based on the one employed at the National Geophysical Data Center, Boulder Colorado (see: ftp://ftp.ngdc.noaa.gov/STP/SOLAR_DATA/CATALOGS/Solar_Observatories_List ), with a few exceptions. In particular, the code GREN is preferred to GREE for Greenwich; the codes DEBR and GYUL are introduced for the Debrecen and Gyula sites of the Heliophysical Observatory, Hungary; and, since the code MWIL is used for the Mount Wilson Observatory (Los Angeles), it seems more logical to use MMAR (rather than MONT) for the Astronomical Observatory at Monte Mario (Rome).

2.4 B.4 Detailed Notes on the Observatory Codes Presented in Table 1

The photoheliograph was moved from Greenwich to Herstmonceux Castle, Sussex, on 02 May 1949. The last photograph of the Sun taken at Greenwich was on 02 May, although a second photograph was taken on the same day with the re-erected Dallmeyer photoheliograph, strapped to the Newbegin 6¼-inch refractor in the 22-foot dome at Herstmonceux Castle (Howse 1975). The code ‘G’ is used for Greenwich in the printed publications (RGO–POBA) within the interval 1874 – 1949 (02 May); the code ‘G’ is used for Herstmonceux in the printed publications within the interval 1949 (03 May) – 1955; and the code ‘H’ is used for Herstmonceux in the printed publications within the interval 1956 – 1976. Therefore, as indicated in Table 1, the new code GREN is used up to 02 May 1949 and the new code HERS is used from 03 May 1949.

The code ‘Mt. W’ is used for the Mount Wilson Observatory in the printed publications (RGO–POBA) within the interval 1874 – 1958; the abbreviated code ‘W’ is used in the printed publications within the interval 1959 – 1966; and the code ‘P’ (Palomar) is used in the printed publications within the interval 1967 – 1976.

The code ‘Y’ is used for the measurements on two days in 1929 that were derived from plates provided by the Yerkes Observatory. The introduction to the Greenwich Photo-heliographic Results, 1929, states: “The Director of the Yerkes Observatory, Washington kindly lent for measurement plates taken on 30 June and 6 November. The measures made from these plates have been included in these Results, thus preserving the daily measures of spots and faculae”. The code given in the “Positions and Areas of Sun Spots and Faculae” section of the Results on both 30 June and 6 November is ‘YERKES’ (in full), whereas the single-letter code ‘Y’ is given in the “Total Areas of Sun Spots and Faculae for Each Day in the Year (1929)” section of the Results. A report from the United States Naval Observatory (Washington) for the interval 1927 – 1928 (i.e. the year ending 30 June 1928) includes the following statement: “Publication of the current solar observations in the Monthly Weather Review has been continued, Harvard Laboratory, Yerkes, and Mount Wilson supplying dates missed by the Naval Observatory” (Reports of Observatories 1931). A similar report from the Yerkes Observatory for the interval 1928 – 1929 includes the statement: “Heliographic positions of the sunspots were measured on 30 days for completing the series published by the Naval Observatory in the Monthly Weather Review” (Reports of Observatories 1930). Moreover, a search of the files of solar images at the Yerkes Observatory has confirmed conclusively that the plates for 30 June and 6 November 1929 were indeed supplied to the Royal Greenwich Observatory by the Yerkes Observatory; the 12-inch telescope was used to obtain these observations (W.H. Osborn, private communication, 2011).

The full code ‘EBRO’ is used consistently for three plates kindly lent by the Ebro Observatory, Tortosa, Spain in 1930 (23 August, 23 and 24 December), whereas the single-letter code ‘E’ is used consistently for two plates kindly lent in 1925 (23 July and 26 November).

Furthermore, on 20 days in 1888 both an Indian and a Mauritius photograph were measured (6 – 11 November, 13 – 22 November, 27 November and 7 – 9 December). In these cases the code ‘M. and I.’ is used in the printed publications (RGO–POBA), although it is not explained how the measurements from two photographs on the same day were actually combined.

2.5 B.5 Geographic Coordinates and Altitudes of the Solar Observatories

Table 1 also gives the geographic coordinates and altitude of each solar observatory that has contributed to the Greenwich Photo-heliographic Results (1874 – 1976), along with brief details of the appropriate range of dates and the total number of photographs supplied by each observatory that were used to derive the published measurements (RGO–POBA). The following notes provide sufficient information to explain, albeit briefly, how the values in Table 1 have been determined. With the aid of the following information, it should be relatively simple to include corrections, improvements and refinements in the future.

The basic information has been extracted from The Astronomical Almanac and The Nautical Almanac in the belief that such information is presented to a reasonably uniform standard. Whenever practicable, however, the precision has been confirmed and occasionally refined; in such cases acknowledgement is made to the individual scientists and curators who have provided confirmation or greater precision. Early listings of the geographic coordinates of those solar observatories that were operational towards the end of the nineteenth century can also be found in Liste Générale des Observatoires, etc. (Lancaster, 1886, 1890), In addition, specific scientific publications are referenced [in parentheses] if they provide further background information on the particular solar observatory.

In summary, the information presented in Table 1 has been compiled using the following specific bibliographic sources:

  1. 01.

    CAPE: Astronomical Almanac (2010). Confirmation and additional precision provided by I. Glass and C. Hettlage.

  2. 02.

    DEBR: Astronomical Almanac (2010). Confirmation and additional precision provided by T. Baranyi. [See also: Dezső (1982).]

  3. 03.

    DHRA: Astronomical Almanac (1990).

  4. 04.

    GREN: Nautical Almanac (1941). Confirmation provided by R. Higgitt (Curator of History of Science and Technology, National Maritime Museum, London). [See also: Howse (1975).]

  5. 05.

    GYUL: Astronomical Almanac (2010). Confirmation and additional precision provided by T. Baranyi. [See also: Dezső (1982).]

  6. 06.

    HARV: Astronomical Almanac (2010). Confirmation and additional precision provided by A. Doane (Curator of Astronomical Photographs, Harvard College Observatory).

  7. 07.

    HERS: Nautical Almanac (1959). [See also: Howse (1975).]

  8. 08.

    KODA: Astronomical Almanac (2010). Confirmation provided by K. Sundara Raman. [See also: Kochhar (2002).]

  9. 09.

    MAUR: Nautical Almanac (1941).

  10. 10.

    MELB: Nautical Almanac (1941). Confirmation provided by B.A.J. Clark. [See also: Clark and Orchiston (2004).]

  11. 11.

    MITK: Astronomical Almanac (2010). [See also: Nagasawa (1967).]

  12. 12.

    MMAR: Astronomical Almanac (2010). [See also: Cimino (1967).]

  13. 13.

    MWIL: Nautical Almanac (1941). [See also: Howard (1969).]

  14. 14.

    SCHA: Astronomical Almanac (2010). [See also: Wöhl (2005).]

  15. 15.

    TORT: Astronomical Almanac (2010). Confirmation and additional precision provided by J. Battló and J.J. Curto. [See also: Selga (1915).]

  16. 16.

    USNO: Nautical Almanac (1941). Confirmation and additional precision provided by G.R. Chester (US Naval Observatory). [See also: Peters and Wagman (1930).]

  17. 17.

    YERK: Astronomical Almanac (1981). Confirmation and additional precision provided by W.H. Osborn (Yerkes Observatory). [See also: Reports of Observatories (1930, 1931).]

  18. 18.

    ZURI: Astronomical Almanac (2010). [See also: Waldmeier (1968).]

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Willis, D.M., Coffey, H.E., Henwood, R. et al. The Greenwich Photo-heliographic Results (1874 – 1976): Summary of the Observations, Applications, Datasets, Definitions and Errors. Sol Phys 288, 117–139 (2013). https://doi.org/10.1007/s11207-013-0311-y

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