--- In
cybalist@yahoogroups.com, "Geraldine Reinhardt" wrote:
> Nevertheless, here goes. Venus is considered the brightest in
> the evening sky (when compared to the other planets and stars).
Let's be more precise: Venus is the brightest object in the
sky (Sun and Moon apart), be it evening or morning. Its light
is due to sunlight reflected on the dense reflecting clouds
which form three compact layers in its atmosphere, up to some
68 km of height.
> Isn't this good enough?
For what?
> Yet, you claim that Venus and it's brightness needs to be
> compared to the Morning Star.
You made a curious statement, about Venus being brighter in
the evening than by morning. This statement is simply false.
The brightness depends essentially on Venus' "phase" with
respect to Earth (pretty similar to Moon's phases) and this
is the result of a given geometrical configuration for the
three-body problem (Sun, Venus, Earth). This configuration
changes very slowly [if you are amused, you may make some
home computations for yourself, with Earth at around 1 a.u.
from the Sun and a revolution period about 365.25d, and Venus
at a distance of 0.72 a.u. and a period of 225d, to find out
what phases should be observed and when -- you may consider
for simplicity the orbits circular and in the same plane].
The phase change could be _hardly_ noticed between evening
and morning, there is simply no time for a major change;
besides that, even the sign of the small phase change is
either positive or negative depending on relative geometry
change.
If there is to find a sistematic difference between evening
and morning brightness, it should be linked eventually to
terrestrial atmosphere, presence of fine fog, industrial
activity over the daytime, etc. - but averaged, they should
not count too much.
> All I know is that the evening sky consists of reflected
> light while the morning sky is more profound.
Where did you get that information? Daytime sky is blue because
of sunlight dispersion in the atmosphere (law 1/(lambda)^4 and
sunlight spectrum are responsible for the averaged light blue).
Night sky is essentially black, with some slight dispersion
of light from moon, stars and planets, but also public lights
in the cities could be reflected on clouds (if any) and suffer
some dispersion. With no clouds there is no reflection; out of
the atmosphere, the "sky" is black.
With respect to a previous post:
> Yet Venus IS the evening star.
Venus is both Evening and Morning Star. In Romanian there is
one "Luceafar" which can be "de searã" (Evening Star) or "de
dimineaTã" (Morning Star). The corresponding sky object is
obviously the very same.
> Could the answer lie in the possibility that both Venus and
> Earth are similar? Likely mirror images of each other?
The answer to what?
Earth and Venus are somehow similar in dimensions and gravity,
but this observation is due to modern astronomy and was by no
means known by ordinary people 2000 years ago. There is no way
to simply look at a distant cosmical object and to have a
revelation about its' size: you have to determine first its'
angular size correctly and the distance.
Out of that, I find no link between the similarity in size
and the name. Why should one pick a name over another because
tha planet might have a similar radius?!
Regards,
Marius Iacomi