 |
|
| Saturn’s period | |
| «
SALV. […] Such
is the arrangement: the larger an orbit is, the longer it takes to revolve
about it, while for the smaller orbits, time is shorter: Saturn, therefore,
describing a larger circle than that of all other planets, revolves in
thirty years. Jupiter takes twelve years to
revolve in its orbit, which is smaller; Mars takes two years; the Moon
only takes a month, to go around its orbit which is very small in size.
In a similar way we see the Medicean Stars: the one nearer to Jupiter revolves
in a very short time, in about forty two hours; the second star revolves
in three and a half days; the third star in seven days, and the farthest
in sixteen days […] »
(1)
|
|
| z | |
| Saturn has a composite structure | |
| «
[…] On the 25th, I again
started to observe Jupiter at the east, in the morning, together with all
its Medicean Planets, and discovered another extravagant wonder. I wish
both your Serene Relatives and Your Highness to become acquainted with
my discovery, but keeping it secret until my next work is published: in
case others should tell you about this wonder, it is my wish that, Your
Highness and Your Relatives, should be aware I was the first to observe
this event, even though I am quite sure nobody will see it, before I can
give news of it:
the star of Saturn is not a single one, but an arrangement of three, that almost touch each other and never move or change; with respect to each other; and they are placed on a line along the Zodiac, the one in the middle being about three times larger than the other two on the sides; and they are situated in this form, |
|
 |
|
| which I shall show to Your Highnesses,
during this Autumn, when it will be easier to observe all the celestial
wonders, as all the planets will be above the horizon.
» […]
« [...] the one in the middle is quite larger than the other two at the sides; situated one at the east and the other one at the western side, all of them on the same straight line and having the shape of a hat. Rightly, they are not on a line along the Zodiac, but the western one very much raises towards Boreas; perhaps they are parallel to the equinoctial line. » [...] |
|
| z | |
| The structure observed depends very much upon how the spy-glass can magnify matters | |
| « Should observations be carried out with a spy-glass having little magnification properties, it would not be possible to clearly detect the three stars. Saturn, instead, would appear as a star that is slightly long in shape and similar to an olive, as follows: | |
 |
|
| on the other hand, using a spy-glass
able to magnify the surface more than a thousand times, it would be possible
to observe the three globes very clearly. They nearly touch each other
and the maximum partition among them is just that much large as a dark
thin thread can be. […] »
« [...] Five months ago, the spacing was larger. From then onwards it diminished very much. The hat shape of the three stars, however, did not change and I deem they were exactly parallel to the equinoctial line and not to the Zodiac. » (2) [...] |
|
| z | |
| Details on Saturn. Comparison with the other four planets observed | |
| « [...] Is it true, Sarsi, that Saturn, Jupiter, Venus and Mars, when observed by a naked eye do not show any difference in shape and, when observed at different intervals of time, show a very slight difference in size? and that Saturn appears, as in the figure below, when observed with the spy-glass: | |
 |
|
| that Jupiter and Mars always appear
same and that Venus appears in many different shapes? And, even more amazing,
with so diverse sizes? When horned its disc is 40 times greater than when
its shape is round. Mars is 60 times greater at perigee than at apogee,
while, when observed by a naked eye, it only is 4 or 5? Your
answer must be affirmative, as these are logical and unchanging assumptions,
there is no hope that, by means of syllogisms, we can change them.
»
« [...] it
is also desirable, that you should observe with the help of a telescope,
the Star of Saturn extremely well defined and very much different from
others in shape; Jupiter’s disc and Mars’s,
which are greater when near to the Earth and perfectly round and defined;
Venus that has periods during which it shows horned and others in which
it shows defined; even the small globes of the fixed stars and those greater
of the major stars, show up very well defined. To end up, a thousand little
candle flames, very far away and defined so well as if they were near,
are all figures a naked eye cannot see without
the help of a telescope. A naked eye would only see them darkened by foreign
rays and all under the same radiant figure,
» (3)
[...]
|
|
| z | |
| (1)
Selected passages from: Galilei, Galileo, «Le
opere di Galileo Galilei : edizione nazionale sotto gli auspici di sua
maestà il re
d'Italia». Volume VII, see: Liber Liber (2) Selected passages from: Galilei, Galileo, «Le opere. Volume X. Carteggio 1574-1610», see: Liber Liber (3) Selected passages from: Galilei, Galileo, «Il Saggiatore», see: Liber Liber From: "Progetto
Manuzio", an initiative of Liber Liber. A
non-profit cultural association, open to everybody who is willing to
|
|
|
|