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680111ALPO

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             ASSOCIATION OF LUNAR AND PLANETARY OBSERVERS
               Comets Section           January 11, 1968

                       Comet Ikeya-Seki 1967n

     The fourteenth comet of 1967 was discovered in the morning sky
by Ikeya and Seki on December 28th, apparently within minutes of each
other. Tsutomu Seki has recently been sweeping with 5-inch 20 power
binoculars, and he also found Cornet 1966d with these. They give a 3° field
     This comet is going to be within binocular range and circumpolar
for several months, according to a preliminary orbit by Brian Marsden.
He used seven positions from December 29th to January 6th. The elements
are: Perihelion February 26 at 1.69 astronomical units; Argument of
perihelion 72°; Ascending node 255ø; inclination 130°.
	From these elements a comet orbit model can be constructed with
instructions by Steve Larson in the March-April, 1965, Strolling Astronomer

The following predictions are in 1950 coordinates for 0h UT.

                                      delta        r        Mag.
Jan. 10   16h 42m.0    +1° 40'
     15   16  45 .9    +3  47
     25   16  53 .6    +8  53	2.02             1.74       7.9
     30   16  57 .4   +12  00
Feb.  4   17  01 .0   +15  33                               7.6
      9   17  04 .6   +19  38
     14   17  08 .0   +24  18   1.60             1.69       7.3
     19   17  11 .1   +29  38
     24   17  14 .0   +35  39   1.44             1.69       7.1
     29   17  16 .4   +42  21

     Edgar Everhart, Mansfield Center, Conn., picked up the comet on
Jan 5.45 UT. He writes that its magnitude was about 9.5 and looked like
a small globular cluster, but "much harder to see than M10 and M12."
"Hats off to them," the veteran comet-seeker Everhart sayst "This was not
an easy one to discover so close to the bright twilight horizon."

    The next morning Jphn E. Bortle saw the comet from Mount Vernon,
New York. It was at 16h 39m.2 +00° 19' and had a diameter of 2'. By
using comparison stars from a ne3rby AAVSO chart field, Bortle obtained
a magnitude of 8.8. He saw it as "diffuse with little condensation."

     George Van Biesbroeck, Tucson, Arizona, estimated a total magnitude
of 9.1 on the 7th. He reported a coma diameter of 30" and an unsharp
nucleus, 2" across.

     Because of its great perihelion distance, Comet Ikeya-Seki is not
expected to become brighter than 7th magnitude. However, it is an
intrinsically very bright comet with an absolute magnitude of 4.  Marsden
computed the brightness predictions from m = 4.0 + 5 log DELTA + 10 log r.

     Magnitude estimates can be made with the Smithsonian catalog, but
several estimates should be averaged because of the catalog's scatter at
fainter magnitudes. Some AAVSO chart fields that will be of value for
total and nucleus magnitudes are SS Her, S Her, Z Oph, and RS Her.  Between
Feb. 14th and 19th the comet will be close to RT Her and CX Her.  Order
"b" and "d" charts for 13cents each from AAVSO, 187 Concord Ave., Cambridge,
Mass. 02138.  Enclose a stamped return envelope.
     The comet will pass the Keystone of Hercules Feb. 24th, and it will
be near M92 on the 29th.

        Dennis Milon    378 Broadway    Cambridge, Mass. 02139
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ALPO: Comet Ikeya-Seki 1967n Info Sheet
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