1996/97 Mars Sketch

1996/97 Mars Sketch (14)
from CMO #211 (25 January 1999)

-- Densely Reddish Areas:
Solis L, Nilokeras and Tempe in Blue --

Introduction
As we elucidated in #128 p1171 (Jan 1993), the Martian reddish surface can be considered not to emit the shorter-wave blue light and hence the disk should originally look dark through the blue filter. The white clouds or mists however sometimes feature some topographic shapes, to the extent that some markings become occasionally visible. We have so far in this medium not alluded to such an idea as blue-clearing nor absence of the blue haze. Note however that we have never neglected the usefulness of the observation by the use of the blue filters. The blue light easily shows us the presence of the white clouds or/and white haze.
Here we are not necessarily to emphasise the effective use of the blue filters, but rather state that the observations in the integrated light can also frequently produce the wider results influenced by the blue light.

HST images on 30 March 1997 ( left : blue right : red)

Densely reddish areas
Let us recall the HST images (delivered on 20 May 1997 but) taken on 30 Mar 1997 (097°Ls) at ω=094°W which were cited in #191 (May 1997): These clearly show that the blue image (left) of the surface is very different than the one produced from the colour image (right). The set of images is interesting so that we again reproduce them this time with a red image at the right-hand side. At this place it should also be recalled that the schematic map presented at p2050 in #188 produced the similar surface in which we designated the presence of the reddish areas - densely reddish or coral reddish areas. It is easily understood that the densely reddish or coral reddish areas are the places to be taken dark in blue light, while in red light they look light. In #188 we emphasised that the areas were discriminated through the integrated light under good seeing.

WHITBY's drawing in blue
Samuel WHITBY (SWb) obtained an interesting drawing on 17 Apr 1997 (105°Ls) at ω=095°W by the use of Wr80A filter (in addition to Wr21). The Wr80A filter is a colour conversion filter which enhances Mired 313 (or 3200K) to Mired 182 (5500K) by 182-313=-131 (Mired = micro reciprocal degree): This is a blue filter but not so thick and just converts the tungsten light to the daylight. However this proved to be effective in detecting the densely reddish areas, and in fact the drawing shows well the areas as shadowy ones. A white small patch over Tempe is possibly a cloud also seen in HST's blue image.

WHITBY's drawing on 17 Apr 1997 at ω=095°W

Solis Lacus in blue
We tentatively point out that Solis L in HST's red image is somewhat different to the supposed Solis L in HST's blue image. This fake is caused by the fact that the area adjacent to the south of the true Solis L was very densely reddish and furthermore the northern part of Solis L looked faded by a thin white haze. What we want to stress here is not so much this possible fake as the possibility that we may regard this pseudo-Solis L as a true Solis L in integrated light under the usual seeing condition. It is well known that the densely reddish areas look sometimes just shadowy under the usual seeing: We frequently experience that such markings as Ganges and Deuteronilus appear just as shadowy bands without blue filter. As another example, the drawing of Fig 7 cited in #201 at p2247 was made without filters (in 1982) at ω=092°W, from the angle similar to the one by SWh in 1997, but well just like in blue. We also remark that those drawings by H ISHADOH (cited in #201 p2243) and by T NAKAJIMA (cited in #209 p2357) were also made without filters, but depict Montes as dark spots. These clearly prove that our eyes have a wider range function to the shorter wave lengths, and detect the rather red markings as darker ones. By the same token, our eyes even without blue filters catch well the whitish misty things. We thus eventually say that Solis L drawn in the schematic map in #188 p2050, which was based on the drawings made on 25 Mar 1997, must possibly be a pseudo-marking influenced by haze in blue light.

Nilokeras and M Acidalium
Every visual observer must feel difficult how to draw Mare Acidalium and Nilokeras because their shapes appear differently from time to time. Especially we may say it is difficult to grasp well the classical Nilokeras. The above consideration suggests however that this is mainly because Nilokeras is made from the densely reddish band, while Idaeus F and Achillis F are the true dark markings. As well if we could detect the reddish region around M Acidalium to be much shadowy, the shape of M Acidalium would be different to the one we usually see on the HST red images. Furthermore if some white cloud patches or bands exist around this area, the shape must look much different. This may be applied to the case of M Acidalium observed by Elisabeth SIEGEL (ESg) about which we once discussed in 1993. ESg has a keen eye to the shorter wave lengths, and hence it is quite possible for her to have detected a white cloud belt visible in blue light.

Conclusion
It should be recalled that it was not the usefulness of the blue filters that we have tried to emphasise here. Instead we have wanted to call attention to the wider range ability of the naked eyes without filters. We thus conclude that we can place much confidence in the observations through the integrated light, though we admit the markings might turn out to be somewhat different from the ones in red light. We don't also deny the fact that the filters of course help a bit.

(Mn : Masatsugu MINAMI)

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