1996/97
Mars Sketch (13)
from CMO #210 (25 December 1998)
-- HUYGENS versus DOLLFUS --
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I |
t
may look extraordinary to cite a Mars drawing from another kind of journal, but
we here refer to the April-May 1998 issue of
l'Astronomie published by la Société
Astronomique de France (SAF) and cite an interesting
drawing made by Audouin DOLLFUS on 17 April 1997.
This drawing was obtained by the use of a newly reconstructed astroscope à la
HUYGENS.
In April 1995, a congress of the SAF decided to build a telescope
without tube in almost the same way as Christiaan
HUYGENS (1629 - 1695) did three hundred years before from a view point of historical,
scientific and educational interest. In addition to A DOLLFUS, such persons as P
BACCHUS, F BIRAUD, R BOTTARD, 
B DAVERSIN, G FARRONI, J FORT, J-M LECLEIRE, P MOATHY, G PHILIPPON, and
A THIOT joined this project. The issue is a special number having feature
articles on Ch HUYGENS: DOLLFUS himself wrote at least two articles, one was on
the Huygens brothers and some long refractors without tube, and the other on a
report of the practical use of the reconstructed astroscope.
(Fig 1) From the
rear cover of l'Astronomie avril-mai
1998
We try to cite some figures from the Journal, and hope the copies will
be helpful to understand the system of the astroscope.
Roughly speaking, the astroscope first needs a tall
pole or a mast (like the one used on a
The objective glass was polished this time by LECLEIRE. Originally
HUYGENS' objective had an aperture 4.6 
pouces=11.6cm, but the present one 13cm. The focal length was originally 34 pieds=10.5m, while the lens produced here had a 7m. The
eyepiece was also constructed: its focal length was 91.5mm (with the aperture
89mm; big!) so that one can obtain a magnification of 76. In DOLLFUS' case,
however, he describes the astroscope of 10cm, and
uses higher magnifications, and hence the eyepieces must be various including Plössl.
Since the focal length is 7m, the mast must be over 8m, and so they
needed a wider place to put the astroscope. It was
eventually settled in a
(Fig 2) Lozenge à la HUYGENS
designed by Prof DOLLFUS
The Mars Sketch here by DOLLFUS was made on 17 April 1997 22:00
TU (106°Ls). Used 233×10cm Astroscope
(Fig 3). The planet was going away and the apparent diameter was 12.7 arcsecs. The phase angle was 23.5 degrees, and DOLLFUS
detected a defect of illumination. The LCM was 025°W, and M Acidalium was
evident. The other dark marking at upper left must includes Aurora S. The
season was 106°Ls, and hence the area of the north polar cap (2"×1"
in angle) did not well show up, just light obscure.
Professor DOLLFUS also made a sketch of Mars by 100×10cm, and
interestingly compares it with a drawing of Ganymede (of 1.2" arcsecs) anotherly made by the use
of 1000×100cm at the Pic du
Midi. Apart from the contrast, the images are quite similar.
left : (Fig 3) DOLLFUS' Drawing on 17
Apr 1997 at LMC=025°W
right : (Fig 4) HUYGENS' Drawing on 7 Apr 1683
The drawing by DOLLFUS reminds us of a sketch by Ch HUYGENS made
in 1683 (Fig 4). HUYGENS obtained the drawing cited here on 7 April 1683 at
9.5h by the use of a 36 pieds refractor. The
refractor used by him was not any astroscope without
tube, because the idea of the latter was introduced after August 1683. Although
F TERBY made a different interpretation, we may say that HUYGENS also saw M
Acidalium if we compare both drawings.
As detailed in CMO #106 p909 by the present writer, the year
difference 284 is one of the best recurrence year to produce a similar Mars
season as well as the apparent diameter (that is, both planets meet at the
similar points on their orbits). Since 1683+284=1967, HUYGENS' Mars was similar
to the planet in 1967. In 1967, Mars was at opposition on 15 April with the
season 120°Ls, and so the north polar cap must have been smaller than that in
the case of DOLLFUS. This implies in turn that it was hard for HUYGENS to
detect the npc also. (We add that the 1999 Mars is in
another sense a returned planet of the 1683 Mars since 4×79+1683=1999, where 79
is another -not best- recurrence year.)
It is described by DOLLFUS that it was because the diameter of
the south polar cap was of the dimension of 6 arcsecs
that HUYGENS did discover the polar cap on 13 August 1672. Yes, 1672+284=1956,
and the 1956 Mars showed us the south polar cap clearly as well as the great
dust storm. At another page, Professor DOLLFUS compares his detailed drawing of
Mars in 1956 with the famous one by HUYGENS made in 1659 (made on 28 Nov 1659)
both of which describe Syrtis Major and alludes to the decisive progress made
during the 300 years. Prof. DOLLFUS is right, but one thing to be noticed is
that there is a natural reason why HUYGENS did not write the polar cap in 1659, and in this point HUYGENS' 1659 drawing should not be
compared with any drawing in 1956. The reason is simple:1659+284=1943
and hence HUYGENS' Mars corresponds to the 1943 Mars if we refer to the planet
at hand. Mars was closest to the Earth on 29 Nov 1943! when
the season was 345°Ls and φ(=DE)=5°S, and therefore we can say in 1659 nobody could have detected the
south polar cap if a superior telescope could have been used.
N.B.: We should incidentally
note that at p 444 of the April 1992 issue of the Sky & Telescope, Alan BINDER wrote about his experience on an
application of his 7.5 cm Hevelius-type telescope to
the planet Mars in 1988. The south polar cap was detected as well as some dark
markings by the 5.2-metre-long Hevelius. (Hevelius himself used a 45-metre-long telescope.)
(Mn : Masatsugu MINAMI)
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