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These images compare an iconic 20th century photograph of the last quarter Moon with a truly amazing engraving of a similar lunar phase produced in 1636 by the French artist Claude Mellan [1] based on his observations through a telescope made with lenses provided by Galileo. Although the level of detail represented by Mellan is obviously a little less than that shown in the Lick Observatory photo, the overall resemblance is striking. More importantly, as we show on our Photo-Drawing Comparison page, the detail Mellan depicts is virtually identical to what we are able to photograph through our modern 1-inch aperture Galilean replica.
| Mellan (1636) | Lick Observatory |
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The engraving shown here is one of three made for a much larger, but sadly never completed, atlas of the lunar phases envisioned by French nobleman Nicolas-Claude Fabri de Peiresc and executed with the assistance of astronomer Pierre Gassendi. The reproduction appearing here has been adapted from one in Albert van Helden's brief history of lunar cartography at Rice University's Galileo Project. Excellent copies of Mellan's other two engravings (Full and First Quarter Moons) can be viewed at that site. The undated Lick Observatory photograph is adapted from one shown in a recent article by Gingerich and Van Helden about the composition of Sidereus Nuncius, where they compare it to Galileo's much cruder engraving of the last quarter Moon. It should be noted that due to the Moon's librations, the positions of the lunar features are constantly shifting with respect to the limb (edge) and terminator (the line separately dark from light), so lunar phases never repeat exactly. It is at most possible to find photographs which roughly match a particular observation, and the one shown here corresponds only approximately.
This engraving is of interest because it was made during Galileo's lifetime and is believed to be based on observations made through a telescope constructed from lenses provided by Galileo. There is good documentary evidence to establish that lenses were given by Galileo to Peiresc (who had met Galileo as a student in Padua) and assembled into a telescope by Peiresc's friend and collaborator Pierre Gassendi [2].
The story of how Mellan's engravings came into existence is retold in considerable detail in the articles by Pierre Humbert and David Jaffé.
[1] Claud Mellan was one of the most famous artists of his day, and obviously a
man of great talent.
His extraordinary combination of patience and hand-eye coordination is amply demonstrated in what is probably
his most celebrated work and now an
icon of Christian art: his 1649 engraved
Face of Christ
executed in a single, continuous line spiraling outwards from the tip of Jesus' nose.
[2] A seemingly-authoritative French language webpage about the Peiresc/Gassendi/Mellan Moon mapping project by
Yvon Georgelin
suggests that the observations through the Galilean telescope may have been supplemented
by observations through a more powerful long focal length telescope Gassendi had received from the
famous German astronomer/optician Hevelius.
However, Georgelin's webpage appears in turn to rely primarily on the historical
research of G. Bigourdan published during World War I.
Bigourdan unequivocally states that although Gassendi owned many telescopes, the
one he used in making the lunar drawings was received from Galileo himself in 1636
and was for a long time Gassendi's best and most powerful instrument.
He specifically referred to it in his notebooks as his Tubum maxium or Galileanum telescopium.
According to Bigourdan, Gassendi's 4 1/2 foot focal length Hevelius telescope was not received
until 1648, 12 years after the lunar drawings had been completed.
Bigourdan's catalog of Gassendi's astronomical instruments is given in Comptes rendus 162,
p. 896 (1916) and is available on-line, along the rest of his writings on this subject,
through the National Library of France's
Gallica service.
The lenses being sent by Galileo to Gassendi and Peiresc for use in constructing a telescope
are specifically mentioned in a
July 25, 1634
letter from Galileo to Elia Diodati and a
November 10, 1634
letter from Diodati to Gassendi.
Even at the end of his life Gassendi still so treasured his Galilean telescope
that he reportedly made special mention of it in his will.
Although remarkable in both its overall accuracy and detail, and far superior in its photographic realism to any lunar map we are aware of from the 17th century, Mellan's engravings do contain some peculiarities. Two particularly curious features of the last quarter engraving are the two prominent craters (A & B) depicted along the far northern terminator, and the chain of craters (C) shown near the lefthand of the Mare Imbrium basin. Their position to the right of the Montes Alpes mountain chain makes it clear that A & B are the craters Aristoteles and Eudoxus. These craters are hidden far in the shadow area of the Lick photograph. Now it might seem possible that due to the Moon's librations the lunar features may have been oriented differently when Mellan viewed them in 1636, so that even though the views agree as to the position of the terminator at the equator, the alignment might be quite different far to the north and south. Unfortunately, a careful study indicates that Aristoteles and Eudoxus can never be on the sunlit side of the Moon when the terminator passes through Albategnius, as Mellan clearly shows in the middle of his engraving. It would appear that Mellan was not only making a composite of the small fields of view visible through his Galilean telescope, but also combining observations made on different days.
As to the chain of craters (C) not only is it unlikely for craters so far from the terminator to appear in such stark relief, but no such chain currently exists on the Moon and it is highly unlikely that one existed in 1636. Similar problems can be seen with the identification of the craters depicted at righthand edge of the Mare Imbrium. Several of the smaller ones bear no obvious relation to those visible in the Lick photograph.
Despite these minor shortcomings, the images produced by the Peiresc-Gassendi-Mellan collaboration are truly a remarkable accomplishment. Mellan's engravings are probably the most accurate representation we have of how the Moon looked to an early 17th century observer viewing it through a Galilean telescope.
References :
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Images (unless otherwise credited) © Tom Pope and Jim Mosher
Last modified: March 15, 2006