His observations of the dark band at the time were repeatedly made as follows:
26 Feb (083degreeLs) at LCM=155degreeW - 170degreeW
27 Feb (084degreeLs) at LCM=154degreeW - 169degreeW
28 Feb (084degreeLs) at LCM=148degreeW
01 Mar (085degreeLs) at LCM=131degreeW - 151degreeW
(while he could not detect the segment at LCM=185degreeW -192degreeW on 26 Feb). We here reproduce his drawing made on 27 Feb as Fig 1. The apparent diameter was 13.2 arcsecs.
FALSARELLA's drawing on 27 Feb 1997 (084degreeLs)
at LCM=160degreeW by 260x 20cm spec
showing a dark band preceding Olympus Mons
In April NFl also saw the same band on
06 Apr (101degreeLs) at LCM=133degreeW - 141degreeW
The dark band was considered to be similar to the one once alluded to at p1610 of #158, and observed well in 1982 from Japan. It was seen since 7 Mar 1982 (095degreeLs) and the drawing cited in #201 p2247 as Fig 10 is an example which shows the aspect at that time. The apparent diameter was 12.9 arcsecs before opposition. The band was also seen in April 1982.
In 1997, we observed the area from 9 Feb to 14 Feb from Japan when the disk diameter was rising, and the drawing in Fig 8 shown at the same page (#201 p2247) is an example on 10 Feb (076degreeLs) when the apparent diameter =11.5". One round after, we could observe the area from 17 Mar (092degreeLs) through 25 Mar (095degreeLs) when the planet was closest to the Earth.
Hk-065 : HIKI's drawing on 20 Mar 1997 (093degreeLs) at LCM=161degreeW by 340x 16cm spec
Mn-406 : MINAMI's drawing on 20 Mar 1997 (093degreeLs) at LCM=154degreeW 630x 20cm Refra
Unfortunately however the observation of the angle was scarcely made in Japan except at Fukui. An exceptional case was the one in Fig 2 made by Toshiaki HIKI (Hk) at Nagano by the use of 340x16cm spec on 20 Mar at 14:30 GMT (LCM=161degreeW, Hk-065). This is compared here with the drawing (Mn-406) made thirty minutes earlier at LCM=154degreeW by Mn shown in Fig 3. NAKAJIMA (Nj) took drawings of the dark band on the day at LCM=159degreeW & 169degreeW.
As pointed by NFl, the shadowy band is scarcely seen on the images by HST. This must just be because it is different from the so-called the dark marking, but it must be the surface ground itself which appears when it is free from any atmospheric water vapour. Thus the band must be seen if taken through blue light. The naked eyes can catch the wider range of colour waves under good seeing and so the shadowy band is more apparent when the Montes appear to be very whitish bright.
As to this point, the HST images taken on 30 Mar as cited in #191 p2102 are suggestive. On the blue-light disk, we can easily see that the areas that are free from the white mist are not distinguishable from the so-called dark markings. The area in question (the channel between Olympus Mons and the Tharsis ridges) is white at this moment because the area is covered by the morning mist. The observations by NFl and others so imply that the area will be free from the white mist as it moves to the late afternoon side, while the summits of Montes become thickly covered by the white clouds.
We are similarly aware that the canal called Deuteronilus is not exactly the dark marking but mostly the orange-coloured channel which is casually free from the atmosphere. This however appears frequently as a dark band to the naked eyes.
We finally call your attention to the fact that the next opposition will be the last chance to watch the detail of the dark band as well as the white cloud over the evening Olympus Mons.