Re: how long is a day on Venus?

Would you like to see how the old astronomers figured out how long it
takes the other planets to complete an annual orbit by using the
annual orbital motion of the Earth ?.

http://mitpress.mit.edu/journals/pdf/POSC_13_1_74_0.pdf


If you turn to page 86 you will see how astronomers plotted the motion
of Mars in terms of the stellar background broken into
constellational divisions.


You then compare the orbital cycle of Earth with that of Mars by
taking note of how many times the Earth overtakes Mars,in the words of
Kepler himself -


"Copernicus, by attributing a single annual motion to the earth,
entirely rids the planets of these extremely intricate coils [spiris],
leading the individual planets into their respective orbits
[orbitas],quite bare and very nearly circular. In the period of time
shown in the diagram, Mars traverses one and the same orbit as many
times as the 'garlands' [corollas] you see looped towards the centre,
with one extra, making nine times, while at the same time the repeats
its circle sixteen times "


Using this procedure for Venus,Kepler could then affirm through his
10th argument for heliocentricity why the Earth's motion between Venus
and Mars replaced the Ptolemaic conceptions of the Sun's position and
motion between Mars and Venus around a stationary Earth.


Argument 10


" The 10th argument,taken from the periodic times, is as follows; the
apparent movement of the Sun has 365 days which is the mean measure
between Venus' period of 225 days and Mars' period of 687
days.Therefore does not the nature of things shout out loud that the
circuits in which those 365 days are taken up has a mean position
between the circuits of Mars and Venus around the Sun and thus this is
not the circuit of the Sun around the Earth -for none of the primary
planets has its orbit arranged around the Earth,as Brahe admits,but
the circuit of the Earth around the resting Sun,just as the other
planets,namely Mars and Venus,complete their own periods by running
around the Sun." Johannes Kepler


If you absorb the representation, known as the Panis
Quadregesimalis,on page 86 you will be repayed a thousand times over
in enjoying how they figured things out from an orbitally moving
Earth.It is a shared astronomical heritage so you enjoy it as coming
from brilliant people who knew what they were doing. The astronomical
explanation will look fresh to you insofar as most here are into
celestial sphere 'predictions' and hardly take account of the active
motions of the Earth around the Sun along with the other planets.





On Jan 28, 10:18 am, "kajlina" <china_...@xxxxxxxx> wrote:
The period of rotation of Venus is 243 days while its period of
revolution is 225 days.
1.One day on Venus amounts to how many days on Earth?
2. If Venus's direction of rotation was the same as its direction of
revolution, then one day on Venus amounts to how many days on Earth?

I think both answers are 243 days. I suppose whatever the direction of
rotation is, the period of rotation doesn't change. Am I correct?

.

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