Venus pentagram: true or false?
No Hassles (Thanks, Coolgoose!)
Brown's Da Vinci Code. It claims that Venus traces a "perfect
pentagram" through the sky, a claim echoed in many other sources online
including Wikipedia.
Unfortunately, I do not understand how this is possible in any
meaningful way. Venus passes the Earth in its orbit (inferior
conjunction) five times in eight years (less two days). (As seen from
Venus, each conjunction is five days apart; the same side of Venus
faces the Earth each time) Trivially, yes, this means that the Earth
is roughly 8/5 of a year ahead each time, so the Sun (with Venus close
by) is in a different part of the zodiac each time, and these points
can conceptually be linked up as a five-pointed star with the Earth in
the middle.
However, the claim seems often to be taken to mean more - i.e. that the
position of Venus makes some symmetric figure when considered in a
geocentric frame of reference against the fixed stars. I find myself
doubting this now, because the Earth and Venus are in different
positions in their orbits at each conjunction, and the orbits should be
differently inclined with some change in orbital speed due to
eccentricity. I'd think this would mean that even the positioning of
the points of the zodiac would be imperfect, and when actually looking
at the position of Venus in the sky at different "points" of the
pentagram that it'd be all over the place. But I can't readily prove
that to myself from first principles.
It would be curious to see what the apparent position of Venus really
traces out as over time. Is there a program that can readily calculate
and display this? Also it would be nice to mark out where Venus is
located in this figure at the end of each Venereal day.
Bill Owen
No apologies necessary; it's a mighty good read, even if the author
did take some liberties with the science (not to mention the history or
the theology).
If you forget about eccentricity and inclination, a listing of the
longitude of Venus at inferior conjunction (say) does show that
successive conjunctions are separated by close to 8/5 of 360 degrees,
and that after 5 successive conjunctions you're almost back to where
you started. Plot these points on a circle, connect them with straight
lines, and you've almost got a five-pointed star. Now change to a
slowly rotating coordinate system (one revolution every 1300 years or
so), and the five points of the star *will* stay constant. That's
a paraphrase of what you wrote in your second paragraph. And I think
that's really all that the pentacle folks have in mind.
Of course Venus's orbit really is inclined to the ecliptic, and neither
planet is in a circular orbit (although Venus comes close), and the two
planets perturb each other significantly. So you get retrograde loops,
or sometimes Z shapes instead of loops, near inferior conjunction.
There are lots of programs and websites out there which will do the
calculations and make fancy plots. I'll let others list them, as I
don't use any myself except for what we grow here at JPL.
Hope this helps.
-- Bill Owen, w...@jpl.nasa.gov
William Hamblen
> Apologies for a silly question engendered by a silly book, i.e. Dan
> Brown's Da Vinci Code. It claims that Venus traces a "perfect
> pentagram" through the sky, a claim echoed in many other sources online
> including Wikipedia.
The apparent path of Venus as seen from the Earth with respect to the
Sun is roughly a 5 sided figure, but it isn't a perfect pentagram by
any means. It's loopy and squashed.
--
The night is just the shadow of the Earth.
Florian
>Sun is roughly a 5 sided figure, but it isn't a perfect pentagram by
>any means. It's loopy and squashed.
Does someone have a link to an image of this so called pentagram? I just ran Venus through the evening sky for 2005 in a planetarium program and the planet made a sort of a figure-8 pattern. What does this pentagram look like?
-Florian
Peter Abrahams
Bill Owen answered this as well as I can, but I can add, that I also
read 'that book' and thought it was an evening well spent, except I
didn't see one word that made me think anything was true....
When I found the section on Venus' pentagram, I pulled out one of my
favorite books:
Schultz, Joachim. Movement and rhythms of the stars.
Edinburgh: Floris, 1986 (transl. from German 1963).
Which is full of beautiful drawings of celestial movements - planets,
eclipses, sun, moon, stars.
On p121 is an image of "The geocentric Venus orbit 1960-68", with earth
at the middle, and the constellations at the rim, with Venus tracing a
loopy round 5 pointed star - looks more like a five pointed flower.
Then the next pages show 'Distribution and sequence of the superior
conjunctions of Venus and Sun 1952-61', and then inferior conjunction -
traced in a five pointed star.
I'm sure a planetarium program can replicate these if the right input is
provided....
good luck
Peter
=============================================
Peter Abrahams telscope.at.europa.dot.com
The history of the telescope and the binocular:
http://home.europa.com/~telscope/binotele.htm
No Hassles (Thanks, Coolgoose!)
>at the middle, and the constellations at the rim, with Venus tracing a
>loopy round 5 pointed star - looks more like a five pointed flower.
Is this the image you're talking about?
http://www.arcomnet.net.au/~vincent/images/Venus72.gif
When I saw this picture, I couldn't make sense out of it. If the signs
of the zodiac (I think) are at the edge of the figure, then shouldn't
Venus be crossing them? It can't be north of Earth's orbit all the
time! And it still doesn't make sense that its apparent position would
be so symmetrical...
Paul Schlyter
No Hassles (Thanks, Coolgoose!) <noha...@coolgoose.com> wrote:
>> On p121 is an image of "The geocentric Venus orbit 1960-68", with earth
>> at the middle, and the constellations at the rim, with Venus tracing a
>> loopy round 5 pointed star - looks more like a five pointed flower.
>
> Is this the image you're talking about?
>
> http://www.arcomnet.net.au/~vincent/images/Venus72.gif
>
> When I saw this picture, I couldn't make sense out of it.
Think of it as a Ptolemaic representation of the motion of Venus, as
seen from the north ecliptic pole. The Earth is in the center if the
picture. The dotted circle is where the Sun moves. And that long
line with loops represent the motion of Venus: the loops are when
Venus is in retrogade motion, near inferior conjunction, and this is
also when Venus is nearest us.
> If the signs of the zodiac (I think) are at the edge of the figure,
> then shouldn't Venus be crossing them?
No -- the zodiacal signs is merely the rough way by the astrologers to
represent ecliptic longitude. Think of the outermost circle of that
figure as the intersection between the "celestial sphere" and the
ecliptical plane.
> It can't be north of Earth's orbit all the time!
It isn't -- think of that figure as representing the plane of the
ecliptic, and also ignoring the inclination of Venus' orbit, which
would put Venus in the Earth's orbital plane all the time. This is of
course not correct, but it is a fairly good first approximation.
> And it still doesn't make sense that its apparent position would
> be so symmetrical...
Why not?
OK, the image is oversimplified - it assumes that Venus returns to
precisely the same position relative to the Earth and the Sun after
8 Earth years. This is of course not the case, but Venus does come
quite close.
If you draw the ecliptic geocentric position of Venus over a period of
8 years, you will end up with a figure which looks pretty much like
this one. Another similar figure can be found here:
http://elizapeter.eresmas.net/venus.jpg
and here's a Java applet which draws geocentric positions:
http://www.venus-transit.de/geocentric/index.html
--
----------------------------------------------------------------
Paul Schlyter, Grev Turegatan 40, SE-114 38 Stockholm, SWEDEN
e-mail: pausch at stockholm dot bostream dot se
WWW: http://stjarnhimlen.se/
Peter Abrahams
really could not have done it. I can 'get it' graphically but the details
are beyond me.
I like to think about the motions of the planets (one or two at a time) and
try to visualize it. Or just try to visualize all the motions of the earth
- it really makes positional astronomy even more impressive - how do they
know that some asteroid will pass in front of some star, years from now -
when the surface of the earth is traveling in a half dozen different
motions.
It is a great way to try to put yourself to sleep at night.
Peter
--