When the Apparent
Diameter Exceeds
25 Seconds of Arc
Akinori NISHITA
THE fact that the present apparition is exceptional has been known
since the list of the Martian oppositions from 0000AD onward was published by J
MEEUS in the Astronomical Table of the Sun, Moon and Planets, 2nd Ed (Willmann-Bell, Inc. 1995) and has been aroused
especially since Jeff BEISH gave a talk in Yokohama in March 2002 (CMO #258 & #259). See also J MEEUS: More Mathematical Astronomy
Morsels, 1st Ed. 2002.
Plainly speaking, the present
opposition is rare in various respects, but its minor feature is that its
apparent diameter δ attains 25 arcsecs in August. The Mars
observers who have been active have never met with the 25arcsec Mars if he did
not observe the 1924 Mars. Even our colleagues M MINAMI (Mn) and T NAKAJIMA (Nj) who have been involved with
Mars since 1954 have never watched such a big Mars.
After the 1924 great opposition, the
planet Mars was at perihelional opposition four times on
27 July 1939 δmax＝24.13"
07 Sept 1956 δmax＝24.76"
12 Aug 1971 δmax＝24.91
22 Sept 1988 δmax＝23.81"
and hence the
diameter was never larger than δ＝24.9". Those who does not
know the big Mars before 1988 don't know therefore even the 24 arcsec Mars. In
1939, Don PARKER as well as Mn and Nj were born, and hence those who knows the
1939 apparition must be older than these mentors. (We
hear S MURAYAMA and A DOLLFUS, both born in 1924, are still active observers
who observed the 1939 Mars.)
The following just gives information about the period the planet's
angular diameter is larger than 25 arcsecs this August. As seen from the
Astronomical Almanac 2003, it seems to reach 25 arcsecs on 22 August at around 7 h GMT. It will reach 24.91" of the maximum in
1971 near the end of 20 August since the diameter on 21 August at 0 h GMT
attainsδ＝24.93". On the other hand, the
planet's diameter will cease 25 arcsecs on 1 September around at 15h GMT. BEISH's
Wimp gives a bit longer period: that is from 21 August to 2 September.
As to a rough sketch of diameter from
August to September, see:
Almanac Winp
01 Aug 22.36" 22.3"
05
23.04 23.0
09
23.66 23.6
13
24.20 24.2
17
24.63 24.6
21
24.93 24.9
25
25.10 25.1
29
25.11 25.1
02 Sept 24.98 25.0
06
24.69
24.7
10
24.28 24.3
14
23.75 23.7
18
23.12 23.1
22
22.42 22.4
26 21.67 21.7
30 20.89 20.9
As seen here, the diameter 23.8"
will be attained on 10 August.
In 2005, the maximal diameter will be
attained on 30 October and readδ=20.17", and a comparison graph as a
function of the season is given above.
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