CMO/OAA Cahier #06

Nix Olympica/Olympus Mons?


HE Mars Map by Shiro EBISAWA (published in 1954) looks similar to the well-known ANTONIADI Map (published in 1930) but is said to be quite different in that the former compiles several new markings as well as several deformations of the dark markings newly known since the times of E M ANTONIADI. For example, the position of Nix Olympica in EBISAWA's is centred about at (137W, 23N) while it was nearly at (128W, 21N) in the original ANTONIADI Map. EBISAWA's value of Nix Olympica is based upon the photographic data taken by LYOT and CAMICHEL in 1941, while ANTONIADI employed the value something old obtained by SCHIAPARELLI in 1877 - 1890. (We should note however that ANTONIADI himself secured the values (136W, 21N) and (132W, 16N) in 1911 and 1926 respectively. This clearly shows that the ANTONIADI topographic map was mostly intended to incorporate not his original findings but the foregoing veterans' results. It should be remarked that the latter value by ANTONIADI is not so different to the recent value by the US Geological Survey.


How about then the Tharsis ridges in EBISAWA's? Arsia Silva, Pavonis L and Ascrus L are located at the different places than in ANTONIADI's. If these correspond to the modern Montes: Arsia Mons, Pavonis Mons and Ascrus Mons respectively, as far as we judge from the aspects in the topographic map produced by the US Geological Survey, they should be centred at (120W, 9S), at (113W, 1N) and at (104W, 11N) respectively, and these values are apparently different to those in EBISAWA's classical map. The position of the summit of Olympus Mons is also located near at (133W, 18N): This differs from the position in EBISAWA's.

Iuvent Fons is an interesting point since it is quite dark and tiny, and hence it once selected as a standard site on the Martian surfaces to fix relatively other markings (for example by DE VAUCOULEURS for the sake of the Viking flights). The position of Iuvent Fons was fixed by him based on the photometric observation in 1941 and 1958 and can be checked in his article entitled A Low-Resolution Photometric Map of Mars", Icarus 7 (1967) 310 to be (63W, 5S), while US Geological Survey's result pins the marking down at (62W, 4N). [DE VAUCOURLEURS' planning chart in 1971 (S&T May 1971) employs the value (62W, 5N).] It should also be noted that the rather well-known name of Nodus Gordii is not identifiable with a particular marking in Memnonia of the new map by the US Geology Survey.


The Mars in the coming apparition will show the area of the Tharsis ridges and Olympus Mons in a favourable moisturable season and at the same time will pass nearly the sub-Earth point, and hence these differences or confusions stated above should be kept in mind.


CMO #144 (25 April 1994) p1385

NB: The reason why the measurements of the position of the volcano summit are often deviated from the real position seems to be because of the misleading presence of a white roll cloud which lies rather on the following flank. On the occasion of the opposition in 1997, Takashi NAKAJIMA (Nj) and the present writer (Mn) had a good opportunity to face to the CM transit of Olympus Mons on 18 March, and both alternatively watched 20 times the moving of the Olympus Mons summit from 11:00 GMT to 11:47 GMT, and obtained the value Ω=135W as the position of Olympus Mons which was slightly larger than the value given by the US GS. As to this observation, we recorded in the OAA Mars Section Report #10 in CMO #188 (10 April 1997) p2043. The following is an extraction:


Olympus Mons, CM Transit: It is usually said that the planet was at opposition on 17 Mar at 08h GMT this apparition. It should however be noted that the three bodies, the Sun, the Earth and Mars, do seldom lie on a line, but on a plane making a triangle even if it is a big obtuse one. The opposition therefore should be classified by definition since we have an infinite numbers of such planes. The above opposition date is derived ecliptically. It is also possible to choose another plane by the use of the right ascension of the planet. This opposition occurred on 18 Mar at 11h GMT.

On 17 March NAKAJIMA (Nj) and MINAMI (Mn) (at the Fukui City Observatory using a 20cm Refractor) noticed Olympus Mons to be slowly passing the imaginary CM derived by the presence of the bright npc, and hence they tried on 18 March the CM transit observations of Olympus Mons (just as a ceremony). They began from 11:00 GMT (ω=127W), just the opposition time, and made alternately 20 times CMT timings up until 11:47 GMT (ω=139W). As was reported Olympus Mons was faint near the noon, and so Nj and Mn frequently made use of a Green filter or Y48. The result was as follows: Olympus Mons was "before" the CM until 11:23 GMT (ω=133W) and "after" the CM after 11:41 GMT. It looked to stay or be passing the CM between 11:26 GMT (ω= 134W) and 11:36 GMT (ω=136W). Nj and Mn hence concluded that the centre of Olympus Mons was located at Ω=135W. [According to the result by the US Geological Survey, the centre of the volcano is at Ω=133W.] This was just a ceremony, but we should say it is very rare for us to come across the case where Olympus Mons transits the CM in the presence of a bright small npc at opposition.


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