THE ASTRONOMER Electronic Circular No 678 1992 Oct 23 19.55UT Ed:Guy M Hurst, 16,Westminster Close, Kempshott Rise, Basingstoke, Hants, RG22 4PP,England. Telephone/FAX(0256)471074 Int:+44256471074 TELEX: 9312111261 Answerback: TA G TELECOM GOLD: 10074:MIK2885 GMH at UK.AC.RUTHERFORD.STARLINK.ASTROPHYSICS STARLINK: RLSAC::GMH GMH at UK.AC.CAM.ASTRONOMY.STARLINK STARLINK: CAVAD::GMH ------------------------------------------------------------------- PERIODIC COMET SWIFT-TUTTLE (1992t) Orbital computations by Brian Marsden, and also by S. Nakano, Sumoto, Japan, have so far failed to link all the observations, even when allowance is made for nongravitational forces. Although a reasonable fit can be made to the 1862 (except October) and 1992 observations, the resulting transverse nongravitational component is so large that the resulting eighteenth-century perihelion time is 15 months too late. Alternatively, although the three perihelion times can be well represented without any consideration of nongravitational forces at all, there are strong systematic errors, amounting to more than 1', in 1862 and 1992. The gravitational orbital elements below satisfy the observations in 1992 and in Oct. 1862 very well, and they also represent the presumed 1737 perihelion time within 1 day. Backward computation of this solution reveals few candidates for earlier appearances of the comet, although the one of -68 fits within 1 year (there being 15 revolutions between then and 1862), and the comet of +60 may also belong. Future extrapolation gives the next return to perihelion as 2126 July 11, although the problem with the computation of the nongravitational forces must introduce some uncertainty; a change by +15 days could cause the comet to hit the earth on 2126 Aug. 14. It therefore seems prudent to attempt to follow P/Swift-Tuttle for as long as possible after the present perihelion passage, in the hope that an adequate independent orbit determination, uncontaminated by nongravitational effects, can be made from mid-1993 (at r = 3 AU and far to the south) to, say, 1998 (when r = 15 AU and an assumed nuclear absolute magnitude of 14 yields an apparent magnitude of 26). Epoch = 1992 Dec. 4.0 TT T = 1992 Dec. 12.323 TT Peri. = 153.013 e = 0.96359 Node = 139.456 2000.0 q = 0.95812 AU Incl. = 113.430 a = 26.31666 AU n = 0.007301 P = 135.00 years IAUC 5636 Extended ephemeris (cf E671) by G.Hurst using EPH.EXE by N.James: m = 4.5 + 5.0 log R + 10.0 log r Date R.A. (2000) Dec. R r Elong Mag. Motion h m o ' (AU) (AU) o "/hr P.A. 1992 Oct 23.00 15 23.01 +52 37.4 1.277 1.276 67.0 6.1 234 120 24.00 15 31.81 +51 48.6 1.264 1.266 67.0 6.0 239 122 25.00 15 40.49 +50 56.7 1.251 1.255 66.8 6.0 243 123 26.00 15 49.03 +50 1.8 1.240 1.245 66.7 5.9 248 125 27.00 15 57.40 +49 3.8 1.229 1.235 66.5 5.9 252 126 28.00 16 5.61 +48 3.0 1.218 1.225 66.3 5.8 256 127 29.00 16 13.64 +46 59.3 1.209 1.215 66.1 5.8 260 129 30.00 16 21.48 +45 52.9 1.201 1.205 65.8 5.7 264 130 31.00 16 29.13 +44 43.9 1.193 1.195 65.6 5.7 267 131 1992 Nov 1.00 16 36.59 +43 32.5 1.186 1.186 65.2 5.6 270 132 2.00 16 43.84 +42 18.8 1.181 1.176 64.9 5.6 272 133 3.00 16 50.89 +41 3.0 1.176 1.167 64.5 5.5 275 134 4.00 16 57.74 +39 45.4 1.172 1.157 64.1 5.5 276 135 5.00 17 4.38 +38 26.0 1.169 1.148 63.6 5.4 278 136 6.00 17 10.83 +37 5.2 1.167 1.139 63.1 5.4 279 137 7.00 17 17.09 +35 43.1 1.165 1.130 62.6 5.4 279 138 Guy M Hurst