================================================================================ Extract of Lunar Occultation records from VI/132B Occultation Archive of Herald D., Gault D., International Occultation Timing Association (IOTA), (2010-2012), held by the Centre de Donn̩es Astronomiques de Strasbourg. Used in "Measurement of the Earth's Rotation 720 BC to AD 2015", by F.R. Stephenson, L.V. Morrison and C. Y. Hohenkerk, published in The Royal Society Proceedings A at the Journals website at http://rspa.royalsocietypublishing.org/lookup/doi/10.1098/rspa.2016.0404 Description of Lunar Occultation Archive VI/132B, (Herald+ 2012) Lunar occultation timings from 1623 to the present time are brought together in a consistent format. The observations have been processed and reviewed to correct a range of data errors. Provisional reductions of the observations are provided. The reductions are based on the JPL-DE422 and -DE423 ephemerides, with limb corrections derived from satellite altimetry from the Kaguya mission. ================================================================================ This extract: We have selected the observations from the CDS archive (described above) with the purpose of deriving the value of DT (=TT-UT) for each observation. We designate the preliminary value of DT used by Herald & Gault in their reduction of an observation in the CDS file by HDT. The reduction of an occultation using this value of HDT produces the residual height - OC in the - CDS file of the star from the lunar limb, reckoned positive above the limb. If dOC is the difference in OC for a change of +1s in time, the value of DeltaT for an observation is thus DT = HDT - OC/dOC. This expression is indeterminate as dOC -> 0. So we have not selected observations with |dOC|<0.2. This file includes other information as indicated below. ================================================================================ File Summary: -------------------------------------------------------------------------------- FileName Lrecl Records Explanation -------------------------------------------------------------------------------- ReadMe-extract.txt 80 . This file extract-lunarocc.dat 107 120908 The file with the extracted data. Byte-by-byte Description of file: extract-lunarocc.dat -------------------------------------------------------------------------------- Bytes Format Units Label Explanation -------------------------------------------------------------------------------- 1- 10 F10.4 yr Year *[xxxxx] Julian Year and fraction of the observation, formed from the date and time. 13- 22 F10.1 d JD *Julian date and fraction of the observation. 25- 34 F10.2 s DT *Delta T for the observation, which is given by DT = HDT - OC/dOC, where HDT, OC and dOC have been extracted from the data, see below. 37- 44 F8.2 --- Wt *Weight assigned to the observation, Wt = 0.09/ERR^2 46 A1 --- Phen [BDEFMORSX?] Phenomena type (4) 48 A1 --- Limb [DBU?] Bright or dark limb (5) 50 A1 --- Meth1 [CEGKMOPSTVX?] First method of timing and recording 1 (8) 52 A1 --- Meth2 [ACEGKMOPSTVX?] Second method of timing and recording (8) 53- 60 F8.1 s HDT *Value of Delta T extracted from Heralds list of Delta T's used in the reduction and given in the file doc.txt file. 61- 69 F9.2 arcsec OC O-C residual - height of the star above the lunar limb. 71- 77 F7.2 arcsec/s dOC O-C change for a time difference of +1.0 second. 78- 87 F10.3 s OC/dOC *O-C residual - height of the star above the lunar limb divided by O-C change for a time difference of +1.0 second. 91 A1 --- Acc [123456789?] Accuracy (18) 92- 99 F8.3 s Accur [0.000,9.999]? Accuracy of time. 100-107 F8.3 ERR *ERR = Error in timing estimated from the parameters Acc and Accur, and the methods of timing, Meth1 and Meth2. -------------------------------------------------------------------------------- Notes Those quantities with an * in column 34, just before the Explanation are not part of Herald's CDS Occultation Archive, but added. Some of these quantities, such as the Year and fraction, DT and the Weight Wt, were used in the weighted least-squares spline fitting process. -------------------------------------------------------------------------------- Note added 2020 December 21 In order to reverse the calculation from the Julian year (Year) given in bytes 1-10 above, to obtain the civil date of an observation in the original CDS data set it is necessary to first calculated the Julian date, viz: JD at 0h + fraction of day = (Year Р1800.0)*365.25 + 2378496.5 For example 1908.0794, which gives the Julian date 2417971.0033249999, and that translates to 1908 January 30 at 12h to the nearest hour. Unfortunately the zero point used for measuring the Julian year from J1800.0 should have been 2378495.0 (i.e. 2 centuries of 36525 days prior to J2000.0 = 2451545.0), which is 1.5 days earlier. Thus, our tabulated values are systematically too early by 1.5/365.25 = 0.0041 of a year. This small systematic error in our tabulation is of no physical significance. -------------------------------------------------------------------------------- The following numbered notes are extracted directly from Herald's ReaMe.txt file. The numbering has not been changed, and are included here to be consistent with the quantities included in this file. -------------------------------------------------------------------------------- Extract from Herald's Notes: Note (4): the code for the Phenomena type is as follows: D = disappear R = reappear B = Blink. The mid-time of a blink event. Usually only occurs during a graze, but can occur in near-graze situations. Duration is specified at col 48. (video) partial disappearance (always >25% of full light). (visual) a short disappearance-reappearance - too close to separately time. F = Flash. The mid-time of a flash event. Usually only occurs during a graze, but can occur in near-graze situations. Duration is specified at col 48. (video) partial reappearance (always <25% of full light). (visual) a short reappearance-disappearance - too close to separately time. M = Miss. The time when the star was adjacent the highest point on the observed or predicted graze profile - although the time might also be simply the mid-time of the graze. Usually only used when other observers in a graze observation have recorded D and/or R events S = Start or resume. Only used in a graze observation, to indicate periods when the observer was observing. E = End or pause. Only used in a graze observation, to indicate periods when the observer was not observing. O = Other [used by ILOC instead of S or E] X = Missing data. A grazing occultation of this star was known to have been successfully observed on this date, but no observations are available. The time and site coordinates are indicative only. Note (5): the Bright or dark limb code is: D = dark limb B = bright limb (including lunar eclipse penumbra) U = umbra of lunar eclipse Note (8): the code for the method of timing and recording is: G = Video with time insertion, times extracted by frame analysis V = Video with other time linking, times extracted by frame analysis M = Video with other time linking, times extracted by replay S = Stopwatch (visual) T = Tape recorder (visual) E = Eye and ear P = Photoelectric K = Key-tapping - including computer keyboards X = Chronograph C = Camera and clock O = Other [details reported to ILOC, but not captured.] A = Time base corrected using adjacent observers. This is only used in Meth2. Note (9): the code for the Time source is: G = GPS (using 1PPS output, NOT GPS screen display) R = Radio signal (standard time signal) N = Network Time Protocol (using NTP software) C = Clock(adjusted by standard time signal) T = Telephone M = Some medium related with standard time signal O = GPS screen display, computer clock not using NTP software (poor accuracy). Note (18): the code for Accuracy (RGO) is: 1 = excellent, very good (+/-0.1s, +/-0.2s) 2 = good, certain (+/-0.3s, +/-0.4s) 3 = fair, satisfactory (+/-0.5s to +/-0.7s) 4 = poor, uncertain (+/-0.8s, +/-0.9s) 5 = very poor, very doubtful (+/-1s) 6 = star faint 7 = perhaps early 8 = perhaps late 9 = uncertain by tens of seconds -------------------------------------------------------------------------------- Acknowledgements: Herald D. and Gault D., International Occultation Timing Association (IOTA), Centre de Donn̩es Astronomiques de Strasbourg. History: 2020 Dec 21 Note added concerning year. ================================================================================ (End) Catherine Hohenkerk, Leslie Morrison, Richard Stephenson 01-Nov-2016 ================================================================================