I thought of this while looking at the recent Questions re: Tidelocking/Long Days
thread, but since it's not directly relevant to that thread, I figured I'd start a new one, rather than trying to hijack that thread.
This suggests that if we assume that Venus's rotation has evolved gradually, and it started out prograde in motion, then at one point it was in the "locked" position, but then became unlocked, and began to slowly rotate in the retrograde direction. There's no way this could happen though, hence catastrophic theories involving collisions are invoked to explain the retrograde rotation.

But this still begs the question as to why Venus is not now tidally locked to the Sun. It might be the case that Venus is still working toward the equilibrium state of being tidally locked to the Sun. However, Venus's rotation is so slow as it is, it shouldn't take millions and millions of more years to lock it to the Sun.

That's why I think that the Earth is involved. Every time Earth passes Venus (at inferior conjunction) Venus always presents the same side to Earth. This relation is so precise, it is difficult to explain away as a mere coincidence (unlike the purported 8:5 orbital resonance). One explanation for this precise relation is that Venus is temporarily tidally locked to the Earth during inferior conjunction, and that this Earth effect balances out the tidal locking effects of the Sun. So the Venusian retrograde rotation is actually in a 3-way equilibrium with both the Sun and the Earth.



Now, my hypothsis actually leads to the following prediction:

1. Since Venus and the Moon have similar geographies in that they both have one side composed of relatively less dense material, and another side with more dense material (i.e. these sides have more anomalous mass concentration or "mascons"); and

2. Since the side of the Moon with the most mascons always faces Earth;

3. Then when Venus is in inferior conjunction with Earth, the side of Venus with the most mascons should be facing the Earth.

I have no idea if this is the case, though. It seems like the answer should be out on the internet somewhere, but I can't find it.

Hence my question: Which side of Venus faces Earth during inferior conjunction?

The dark side?

That's an interesting theory.

There are two parts to confirming it:

Which side is Venus' mascon on?

Where in its rotation is the mascon when it passes between earth & sun?

Earth & Venus are in their own resonance. Is this in sync with Venus' retrograde rotation?

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PW -- Plant Whisperer

There is a connection here.

The Earth/Venus are in an apparently pretty tight 5:8 orbital resonance that's responsible for the historical occult association of pentagrams with Venus. If you draw a circle representing the orbit of Earth, and then draw a point on this circle marking an inferior conjunction, and then draw a line to the point on the circle marking the next conjunction--if you do this five times, you will trace out a pentagram.

Only problem is it's not perfect. The end point of the last line doesn't quite match up with the starting point of the first line. They're off by a couple of degrees. So if you keep drawing, you wind up with a series of pentagrams that slowly regress around the circle.

So, here's the kicker: the side that Venus presents to the Earth tracks the regression of the pentagrams drawn out by the 8:5 orbital resonance! That's what sealed the case in my mind after I learned it.

Gee; I know I heard that recently. [looks around a while]
Here... with an orbital path picture (which is probably why I remember it).

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Numbers are not case sensitive. (me)

Good link. Check out the post by Tony, the inventor of GravitySimulator (a great program that's free). It shows a geocentric universe. The path of the Sun is the yellow line, the inner loops show where the conjunctions occur, revealing the 5-pointed pattern.

The central meridian at inferior conjunction is around 335ºE, currently.

Grant Hutchison

Really. . . . .

Umm.
Really.

One way to check is to use the JPL Horizons system to tell you the central meridian during some known IC, like the transit of 2004.
(I used Celestia, which I've previously checked against JPL while setting up Venus' rotation parameters.)

Grant Hutchison

OK, check out this simple topo map:

Map of Venus

I guess on Venus, they don't mess around with east and west longitude. You'll see that the map starts at 240º and goes for 360º, until 240º is reached again. (Latitude is from about -66º to +66º.) It's like they chose to slice the map this way in order to show the two main sides of Venus. On the left side which goes from about 240º to 60º shows mainly lowlands showing the effects of the major resurfacing event that happened several hundred million years b.p.; I claim this side is analogous to the near side of the Moon, home to most lunar mascons. On the right side going east from about 60º back to 240º shows a region containing lots of less dense highlands, analogous to the far side of the Moon.

Now, 335º is 95º degrees east of 240º; so even though the map doesn't show lines of longitude, 95º is just about in the middle between 240º and 60º (on the western half of the map)--and this is just about where the Earth/Venus tidal resonance hypothesis predicts it should be!

EUREKA!!!

Thank you, Mr. (Dr.?) Hutchison!!!

Only thing to do now, is to come up with a theory that can explain why Earth's tidal effects are not swamped by the much more massive Sun.

And actually, I am sure that someone will quibble that since the Earth/Venus resonance is off by 1 part in 10,000 compared to what NASA says the radar rotation is, then the Earth/Venus resonance hypothesis cannot possibly be true. So, I need to do a bit more empirical work to show that the resonance lies between the 95% confidence interval for the expected error of the radar estimates.

The convention is that retrograde rotators have longitude marked in degrees east of prime meridian, and direct rotators are marked in degrees west. The exceptions, for historical reasons, are the Earth and moon, which go east and west from the prime meridian.

<Bows.>
I answer to either.

You might care to do an internet search for the existing work on this topic: people have been discussing the apparent resonance in the technical journals since 1966, just after the first radar measurements.

Grant Hutchison

And where is the mascon in relation to 335ºE?

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PW -- Plant Whisperer

I haven't a scoobie. I just know what the central meridian is at inferior conjunction; the rest belongs to Warren Platts.

Grant Hutchison

Well, I guess it's back to the drawing board. It turns out that the Venusian lowlands are not analogous to lunar maria, in that lunar mascons are closely correlated with lunar maria, but on Venus, it's just the opposite--gravitational anomalies are highly correlated with topography meaning that the lowlands of Venus have negative gravitational anomalies. (Venus Gravity Field):

Still, there's wiggle room for the resonance hypothesis. The link provided by Dr. Hutchison states the following:

So, the correlation of the resonance with the radar-determined rate of rotation is quite tight. However, I believe the radar rotation result came in before there were detailed topographic maps of Venus. Goldreich and Peale had the similar idea that biggest gravitational anomalies should point at Earth during inferior conjunction, and yet it seems to be just the opposite--Venus's bulge points toward the Sun during inferior conjunction. Which is encouraging; what would tend to disconfirm the resonance hypothesis more would be a longitude facing Earth at something like 245º or 65º.

Here's a better map of Venus that shows lines of longitude. I don't know. . . . When you look at it, is there anything absolutely obvious that would be relevant to the resonance hypothesis?

The quote you just quoted proves your hypothesis

Unfortuantely, it also demonstrates its not entirely original

Thanks, nonetheless. I have always wondered why Venus is not tidally locked to the sun in simple manner

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PW -- Plant Whisperer

On Celestia, I lined up Earth with the sun at the time of the last Venus transit (June 8, 2004 @ 08:19:44 UT), and then headed straight for Venus and landed at longitude 25^o

I assume that this is the same 335^o longitude that Dr. Hutchison reported, since the official Venus longitude is backwards compared to most others, and Celestia must have its own system. Yes/No?

Yes.
There's some residual confusion in how Celestia reports latitude and longitude: sometimes the internal representation leaks out.

Perhaps the easiest thing to do if you want to play with this in Celestia is to download and install my grids overlay add-on, which will let you turn most large solar system objects into white spheroids marked up in latitude and longitude. Then you can observe the behaviour of Venus more clearly.

Grant Hutchison

Thanks again, Dr. Hutchinson!

The term "tidally locked" assumes a rotation equal to it's perodicity of orbit. There is no such thing as "retrograde."

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If I set the budget, we'd have Ares and more. Unfortunately, I don't set the budget, and Ares is just too expensive and too far out for us to accomplish our goals within the budget we were given.

If we halt the ISS, all versions of Ares, and transport Orion and Altair aboard DIRECTv3's Jupiter family of Shuttle-Derived Launch Vehicles, we just might make it back to the Moon by 2020.

I think the orientation of the Moon's tidal lock would be equally stable whether the dense mascons are facing the Earth or are on the far side. Either way the effective long axis of mass distribution would be aligned with the Earth.

Imagine an unbalanced dumbbell in orbit around the Earth, with a heavy weight on one end and a light one on the other end. Suppose it is oriented with the axis about 45 degrees from vertical. Whichever end is lower will be accelerated more, with the result that the dumbbell will rotate toward the nearest vertical position. Remember, an object's gravitational acceleration toward the Earth depends only on its distance from Earth's center, not on its own mass.

If anyone can show us some math that would refute my argument, please fire away. I don't mind being corrected if I make an honest error in this kind of a forum.

No math, but it turns out that the moon's concentration of mass is not pointed at the Earth. IIRC, it's off by twenty or thirty degrees. Does that do it?

I could see how that could happen if the axis of rotation of the Moon and the axis of mass distribution formed a plane that was always edge on to Earth; otherwise, it wouldn't make sense.

Apparently the Moon is irregularly lumpy. Things generally are not physics-101 simple in the real universe.

There are more things in heaven and earth, Horatio, Than are dreamt of in your philosophy.

Make sense in light of that theory? Yes, it does seem to contradict it