Retrograde motion of the Planets

(Dark X Studios) #1

Can anyone explain why some planets (Venus, Uranus and Pluto) orbit opposite than most other planets?

(Mervin Bitikofer) #2

They don’t. All the planets (including Pluto and other discovered planetoids – I believe) all go the same direction around the sun. “Retrograde motion” refers to the apparent (and brief) backward motion some of them trace against the backdrop of stars as the earth speeds past them in earth’s smaller faster orbit.

Correctional edit – The phenomenon I described above is “apparent retrograde motion”. You were correct to be asking about retrograde motion which refers to the actual motions as opposed to the apparent kind. And now that I’ve looked it up, I can confirm that Pluto and all the known planetoids all have prograde orbits. Pluto’s axial rotation, however, is retrograde.

(Mervin Bitikofer) #3

I presume (without confirming this) that the entire asteroid belt too largely goes around the sun the same way. It would be interesting to know, though, how many (if any) rogue asteroids or comets have been discovered orbiting against the flow. The closest any planets come to deviating from the rotational direction around the sun is that some (Pluto and Mercury) have orbital planes at significant angles off of the ecliptic. But they are still much less than right angles (perpendicular), so they still can’t be said to be orbiting backwards.

Uranus does have a planetary rotation that is nearly laid over on its side (97.77 degrees) from its orbital plane. So it could almost be said to have a “backward” planetary spin – but it is more at a right angle than it is backward. Compare that with earth’s 23.5 degree axial tilt which already gives us our seasons, and you can see how uniquely extreme Uranus is in that.

According to the wikipedia entry on retrograde and prograde motions, there are many comets in retrograde orbits (to begin to answer my own question above). Also, Venus has a retrograde rotation (not to be confused with orbital direction). It is interesting that nearly all moons also orbit the planets in the same way as the planetary spin (which means also matching their orbital directions --Uranus and the moonless Venus being excepted of course.) And Uranus’ moons are prograde to Uranus rotational spin (matching the planet’s rotational motion rather than its orbital direction). Triton (of Neptune) is one of the larger exceptions that orbits in the opposite of Neptune’s spin (and the sun’s). So that makes astronomers theorize that Triton was a captured moon rather than formed in its present locale.

(Dark X Studios) #4

Thanks! I recently had someone (a YEC) tell my that the planets that rotate backwards from most planets as well as orbit in an opposite direction means that they couldn’t have formed naturally from the sun

(George Brooks) #5

@DarkX_Studios (and @Mervin_Bitikofer ) :

“Rotating backwards” is a separate issue! That is not the same as orbiting backwards.

Some of the planets orbiting the sun have either an extreme tilt … or I believe there is a case of one of the planets rotating on its axis in the opposite direction.

Cosmologists see these anomalies as evidence of interaction with other massive objects in the 5 billion years of our solar system’s history. You should read some of the amazing descriptions of Jupiter moving around in its orbit, and why scientists arrive at their conclusions.

I find it pretty ironic that your YEC sources get all fussy when it comes to following their perception of natural law … except when it comes to Genesis! Frankly, I doubt if your YEC friend will be impressed with any of the unusual discussions that Cosmologists offer to explain some of the oddities of our own solar system.

(Mervin Bitikofer) #6

Well – it’s easy for anyone to lose the clarification of whether they are talking about orbital motion (how a planet goes around the sun) or planetary rotation (the way the planet spins around its own axis). They were correct to say that some planets spin backwards so long as they meant the latter sort (planetary axial rotation) as they said it. That doesn’t help them make their case that God couldn’t have formed the planets by use of presently theorized means, though. Condensation of a cloud of debris into a system certainly seems to fit what we see – a pretty consistently uniform rotating solar system with a few exceptions not really being all that surprising given other events or collisions that can later modify motions.

(Phil) #7

If you live in a dark area as I do, it is fun to walk outside at night throughout the year, watching the stars move in relation to your setting, and imagine the planets in their orbits in relation to earth. I use the star walk app to help orient me, as I avail myself to El Bano Grande each night (I have no close neighbors, but perhaps TMI :slight_smile:️.
In any case, you can follow the path of Venus on its inner orbit, Mars as it grows near and far in its orbit, occasionally catch a rare glimpse of Mercury in the late evening or early morning, as it is always near the sun, and find Saturn when you know where to look. Jupiter can be seen most of the time due its distant orbit.

Venus, Mercury and Mars are very near the sun at present. Jupiter is out in the night sky.

Which brings up the question posed by someone here in another thread, if you asked Jesus during his earthly ministry “How many planets are there?” , what would he have answered? To the knowledge of the time, he would answer 5, as that was what they observed, and did not think of earth as a planet. Would that have been correct, though not scientifically accurate? Or, would he have said, "8 or 9, depended on what you prefer to call Pluto."
Does that fully human limitation of knowledge then extend to what was believed of Adam and Eve?

(George Brooks) #8


Here’s a dramatic narrative !!

And included is this mention of Venus … which rotates in the opposite direction … essentially because it’s tilt was shifted a full 180 degrees!!!:

“Venus is technically even more tilted, because it rotates clockwise when all other planets rotate counterclockwise, meaning it’s essentially been turned upside-down. But it’s still more or less on the orbital plane, while Uranus is anything but.”

(Mervin Bitikofer) #9

Or maybe he would have said … “27, though this would shock a lot of clever people about twenty centuries from now. Even without their planetoids they still don’t know about a bunch of other big ones I’ve got squirreled away in the Oort cloud.” (Of course he would have said this in Aramaic. I wonder what the Aramaic words for “planetoid” or “Oort cloud” are?)

Seriously though; perhaps it should tell us something that nobody asked him questions like any of these – or even more accessible ones we might have expected they could be curious about such as “how big is the world, really?” or “Is the world really round?” Though those questions were already correctly answered by Eratosthenes centuries earlier, I don’t suppose it was necessarily on the lips or even the minds of the masses.

Apparently such concerns are anachronistic in the widespread sense, and it would be left for “people-in-the-streets” in much later times to become interested in the “mere mechanics” of God’s work. Perhaps only a small percentage of the world is interested in them now!

(George Brooks) #10


Wow… I missed that thread!!! What an excellent question?

Of course, there are other ways to word it so we don’t have to worry about Pluto. And the ancient view of “stars” is a pretty big topic! I would suggest that the Bible already tells us the answer of what would Jesus say:

Firstly, he probably would ask you a question back instead. Secondly, “stars” were considered pretty small… at least as big as a child, but some maybe as big as a ship - - which is still pretty small compared to their actual sizes!

There are plenty of verses in the Bible forecasting when stars will fall to Earth - - completely oblivious to how much destruction that such an event would create - - long before that star ever got to our planet!

Some apologists say that the writers really meant “meteors”… not stars. But I see no evidence at all that the ANE priests and scribes had different words for “stars” and “meteors”.

I can’t even imagine a Biblical scribe of either Testament tackling the distinction between “stars” and “wandering stars” (i.e. Planetes, the Greek word for “wanderers”). How would they describe one versus the other? The latter were actually balls of rock just like the Earth? … but not all the other stars… they were balls of fire that would incinerate Earth if they got too close to us?

If Jesus would have stamped “approved” on “stars falling to Earth” … it shows the limitations the human brain can place on any spiritual being (which is something the Gnostics have been saying for centuries).

Side Note: “My Question” for Jesus -
Since we all know that I’m a Unitarian Universalist … and the last term is at least as important as the first word in our view … you should know that I think God will find a way to bring all Humanity to salvation without violating anyone’s Freewill (I have already mentioned the Chess Master allegory in a prior posting).

So, for the sake of my Universalist curiosity, what would Jesus say about this question?:

If salvation is “solely by grace,” why are not all people saved since in Titus 2:11 we read “the grace of God that bringeth salvation hath appeared to all men”?

We UU’ers like to think Jesus is a Universalist… just like us! :smiley:

(Curtis Henderson) #11

@DarkX_Studios, I just saw this story today:
I don’t know the whole back-story, but I would guess there is sufficient scientific evidence to supporting the hypothesis explaining an unusual rotation by a moon. This isn’t planet-scale, obviously, but at least here is a plausible explanation to unusual rotation behavior.

(Mervin Bitikofer) #12

Maybe Paul too … this curious verse caught my eye this morning: I Tim. 4:10 in which God is referred to as … “the Savior of all people, especially of those who believe.”

(George Brooks) #13


Don’t sweat it. If the explanation isn’t in the Bible … all we have left is science!