THE ASTRONOMER Electronic Circular No 685 1992 Nov 21 17.12UT
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
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PERIODIC COMET SWIFT-TUTTLE (1992t)
Graeme Waddington, Oxford emails:
"The previous integrations of P/Swift-Tuttle's orbit were based on
the osculating elements given on IAUC 5636 (dated October 15).
These elements satisfied the existing 1992 observations and those
of October 1862 very well.
Now, as noted by Brian Marsden (A.J. vol 78, 654 ; 1973), a number
of the October 1862 observations appear to contain large systematic
declination residuals. Integrating the orbit based on these
elements resulted in a perihelion passage in 2126 of July 6.5 and
not July 11 as given on IAUC 5636 (the July 6.5 date was
independently confirmed by Nick James). In order to fit the
published perihelion times for 1737 and 1862, using the IAUC 5636
elements, I found it necessary to include a nongravitational term
of A2 = -0.035. Use of this term brought the perihelion time
forward to 2126 June 29.
The orbit has now been re-solved by Don Yeomans. His current
solution for the orbital elements (MPC 21081) uses 237 observations
from 1737 to 1992 and explicitly omits the October 1862
measurements. Integrating this orbit forward results in a
perihelion passage of 2126 July 12.22 -- on this basis the
closest that P/Swift-Tuttle will get to the Earth is 0.156 au on
2126 August 5/6 when it will have an elongation from the sun of 95
degrees and so should present a good observing prospect to anyone
around in 2126! (it will be around magnitude zero if it's light
curve remains similar to that of the current apparition).
From these new orbital elements I find the times of perihelion
passage during the telescopic era to be,
1610 Feb. 6.31
1737 June 16.07
1862 Aug. 23.50
1992 Dec. 12.33
2126 July 12.22
For the (unobserved) 1610 apparition the comet would have been at
its brightest around the middle of Jan 1610 with a magnitude of
around 5.3. At this time it would have been only about 30 degrees
from the sun in the sky.
Integrating the orbit backwards in time yields favourable naked-eye
apparitions in August 195 BC, August 188 and August 442.
Hasegawa (Vistas in Astronomy, vol 24, 59 ; 1980) lists comets
being seen in all three years. For the great winter comet of 442
enough information is given for its orbit to have been determined -
it's recorded motion does not appear to be compatible with it being
P/Swift-Tuttle, even when we take into account the likely error in
predicted perihelion passage. Of the two comets recorded in 188
the second one was seen in Corona Borealis on 28/29 July 188 and
may be compatible with it being Swift-Tuttle - especially if there
has been an error of one lunar month in converting the date of
observation into the western calendar (in which case it would fit
the current gravitational integration almost exactly)".
Guy M Hurst