Forthcoming 2007/2008 Mars
(10)
Vanishing NPH and the Perimeter of the NPC. II
CMO #334 (25 July 2007)
Masatsugu MINAMI & Masami
MURAKAMI
|
|
|
A |
S described in CMO #329, Forthcoming (5), it
is interesting to watch the vanishing north polar hood (nph): Sometimes some
markings or the perimeter of the north polar cap (npc) can be witnessed seen
through the weakened nph. Here as a sequel of the article in #329, we exemplify
two cases which can probably be seen at the end of this year.
One is to aim watching the Dawes slit at the
same season as DAWES himself detected it in 1864. The season was between λ
=330°Ls and 340°Ls, and so the period from 15 October
to 31 October 2007 must be appropriate. The central latitude is from φ=6°N to 7°N, and so not so bad. We here
show a figure with grids: It is expected the boundary of the nph will be around
45°N
(according to the BAUM- DOLLFUS diagram cited in CMO #109 (25 Sept 1991)
p0944). Table I gives the date and time when the centre of M Acidalium passes
the CM.
The second case is to watch the
thin nph and the perimeter of the npc from the angle at around
ω=180°W at the 
northern
spring equinox. Here Panchaia must be covered by the npc, while the perimeter
(maybe Gyndes) can be seen through as a segment inside the vanishing nph. Table
II also gives the time table when the area is to face us. The boundary of the
npc is supposed here at 57~58°N
(according to the diagram of P B JAMES (see CMO #130-25 Feb 1993: Baum's
diagram points to slightly smaller at 54°N) so that the perimeter of the
dark region of Vastitas Borealis is expected to be visible..
Table I. The transit time at the CM of Ω=030°W (M
Acidalium): In Asia, 02 h JST corresponds to 17 h GMT and so the M Acidalium
faces to them in mid Oct. At the end of October, the European observers catch
the face at the end of October at the meridian. In the US, the observers at the
region where GMT-6h is standard will be able to check M Acidalium at 02 hrs
Local Time at 08h GMT and hence at the beginning of November. The season DAWES
saw the slit was between λ=330°Ls and
340°Ls。