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### 85P/Boethin

The comet was observed in two apparitions: 1975 (4 months arc) and 1985 (2 months arc). The 1997 perihelion passage was extremely unfavourable for observers which could explain why the comet was not observed in that return. P/Boethin is expected back in 2008, but until today (2008-06-19) the comet was not re-discovered. P/Boethin was chossen as target for the extended Deep Impact mission for a rendezvouz in late 2008. In October 2007 attempts with the VLT and the Subaru telescope to re-discover and to observe the comet failed, so another target for DI was choosen: Hartley 2. But despite that comet Boethin is not longer to be visited by the DI spacecraft it might be  interesting and thrilling (to amateurs) to search for the comet.

The comet librates around the 1:1 resonance with Jupiter. As the perihelion distance q is ~1AU, nongravitational forces might have a significant effect on the motion of the comet.

Below two orbit solutions are given, the first one without applying for nongravitational forces, the second one with solving also for A1 (Marsden Style II). Solutions for both A1 and A2 gave no significant result for A2 (value about equal to formal error). NB: The value of A1 is rather large, but there are other comets with similar large A1. The total magnitude m1 was calculated according a formula given by D.Chestnov (comets mailing list 2008-06-17). The rather large activity parameter n=20 might also indicate that nongravitational forces have to be considered. The last two columns in the ephemeris are the (formal !) 1-sigma-uncertainties in RA and DE.

```85P/Boethin
-----------
Epoch  20080514.0 TT  =  JDT 2454600.5    Ref. = MKR-85P-08.1
T  20081216.32166  +/-   0.0024602    Next = 20200708.92078
q   1.147530262    +/- 0.000091375
a   5.112746786    +/- 0.003804677
n   0.085255547    +/- 0.000103046
e   0.775555037    +/- 0.000151178          P    (2000)     Q
Peri   53.54420950    +/-   0.0028407    +0.79786115    -0.60247834
Node  343.47056403    +/-   0.0038467    +0.52690991    +0.71380194
Incl    4.21574852    +/-   0.0002450    +0.29288825    +0.35708072
P      11.56063    +/-     0.01270
H    3.50
n   20.00
From 61 observations (19750205-19860301), RMS = 1.70"

```