Venus pentagram: true or false?

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.

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.

No Hassles (Thanks, Coolgoose!) wrote:
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.

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.

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,

On 2006-02-10, No Hassles (Thanks, Coolgoose!) wrote:

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.

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.


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

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.

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?

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

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. 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...

Thanks very much to Paul S. for answering this question so well; as I
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

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. 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...




--
=============================================
Peter Abrahams telscope.at.europa.dot.com
The history of the telescope and the binocular:
http://home.europa.com/~telscope/binotele.htm