Helaman 12:15 reads, “according to his word the earth goeth back, and it appeareth unto man that the sun standeth still; yea, and behold, this is so; for surely it is the earth that moveth and not the sun.”
If you’re like me you’ve always just read that as Mormon (or possibly Nephi) just having a knowledge of heliocentric astronomy (everything orbits the sun rather than the earth). The author appears to be alluding to Joshua 10:12-13 where the moon and the sun stand still. The last week I’ve been discussing the verse with some other people which have made me rethink the verse.
The main problem with the verse is the author’s assumption that for the sun to appear to stand still it’s the earth that must “go back.” In the past I (and I suspect most people) just read the “it is the earth that moveth and not the sun” part. That “go back” is rather mysterious and undermines this somewhat. In a heliocentric view where the earth orbits the sun to make the sun stand still you’d just stop both bodies. So why does the author say “go back”?
Now you can make a solution where when the earth goes back and the sun appears to stand still. This is just the solution where the orbit and rotation of the earth are synchronized so that one side always faces the sun. (Much like the same side of the moon always faces earth. That doesn’t explain the “go back” part though.
One solution is to assume that the author isn’t just talking about the sun and moon standing still in Joshua but also Isaiah 38:8 where the “sun returned ten degrees.” That is the author is trying to describe God’s power to do both these things yet doesn’t accept the standard geocentric astronomy most ancients held. So for Isaiah in a heliocentric view the earth has to go back.
In this reading all that matters is that the earth moves while the sun is stationary. Thus for the first part of Hel 12:14-15 he’s talking about Isaiah and the middle of verse 15 he’s talking about Joshua. I’m not sure this reading makes sense either though. Note he says that when “the earth goeth back” that it “appeareth unto man that the sun standeth still.” So it seems that in his mind for the sun to stand still you have to move the earth backwards. The fact that is you move it backwards in a specially mathematical fashion you can make the sun stand still doesn’t really explain this formulation. I take him to be saying that if you move the earth backwards in any way the sun would stand still.
If this reading is right then we don’t have here just a normal heliocentric view of the solar system. Instead there’s something very odd going on.
The typical view in the ancient world was a geocentric view of the solar system. That is everything circles the earth and the earth is the center of the solar system. (See the illustration 1 for the typical pre-exilic Hebrew view and illustration 2 for the more Greek inspired view)
Now most people assume that it was just at the end of the Renaissance that heliocentric views of the solar system arose. This isn’t entirely correct. Aristarchus of Samos back around 300 BC came up with a heliocentric cosmos. While it didn’t become popular it remained an influence on many figures. Prior to that the Pythagoreans had a model where a hidden center or second sun was the center of the cosmos. Our regular sun along with earth and all other heavenly bodies then orbit this “central fire.” The sun is more a glass mirror that reflects light from this hidden source. This view is in place at least by the 5th century and may date back earlier. In this system the orbits of the celestial bodies is fastest closest to the central fire with objects farther away going slower until one reaches the fixed stars that are the slowest. The Pythagorean view while not the dominant one, remains highly influential well up through late antiquity and then into the Renaissance and early Modernism.
It’s worth asking about America given our Book of Mormon context. Mesoamerican astronomy was quite like the ancient near east geocentric in outlook. As with many ancient near east thinkers they took the heavenly bodies to not just be balls of rock. They were actual intelligences typically called gods, daemons or angels. Similarly the Mayans saw the planets as gods. In the ancient near east accurate data undermined a simple geocentric view. One might assume it would in ancient America as well. However we don’t have any evidence that happened. There are only four texts that survived Spanish destruction of Mayan and Aztec records. Those texts gave shockingly accurate astronomical data. The path of Venus was predicted accurate to within 2 hours for instance. Impressive for observations without telescopes. They also knew about sidereal intervals to give their accurate predictions for the paths of Mars and Venus. Because of this some have speculated that they actually did have a heliocentric view of astronomy despite no positive evidence that they conceived of the motions using that conceptual model. In any case, the records we have date well after Mormon and thus tell us little about what was believed in 400 AD let alone earlier. Still it is worth keeping in mind that Mayan astronomy rivaled ancient near eastern astronomy in some ways.
As I said the more accurate ones astronomical measurements become the more of a problem a simple geocentric astronomy becomes. The typical solution for this was to add epicycles to correct the orbits. This then explains retrograde motion where the planets appear to go backwards. Ptolemy did this early in the 2cd century. With accurate data a geocentric model actually has orbits that look like illustration 3. Illustration 4 shows how epicycles produce this. The more accurate ones data becomes the more epicycles one has to add.
I think this view of epicycles may actually explains what’s going on in Helaman. With retrograde motion for a planet it will appear from earth to stop and then reverse direction. That is it will “go back.” Illustration 5 shows this for Mars and Illustration 6 is an actual time lapse photography example of this showing that the planet stops twice.
Now while this could explain the “go back” I’m sure you see the problem. This only works for planets when both the Earth and the planet in retrograde are orbiting the sun. If you’re looking at the sun there’s actually no retrograde motion as we saw back in Illustration 3. Thus if this is what Mormon or Nephi were thinking about it’d only work if they had a cosmology like the Pythagoreans where both the sun and the earth orbiting around an other center. That is the sun actually is more like a planet. Further it requires that the sun move much slower than the earth – although that’s less of an issue since as we noted that was already a feature of most cosmologies of this type.
A related objection would be that Hel 12:15 says, “surely it is the earth that moveth and not the sun.” However I think here one could argue that the author is talking about which planet God is changing the movement. So in other words the key concern isn’t verse 15 but verses 13 & 14 where he says,
Yea, and if he say unto the earth — Move — it is moved. Yea, if he say unto the earth—Thou shalt go back, that it lengthen out the day for many hours—it is done
I think this is key to how to read the verse.
In other words I was being led astray in my interpretation by assuming a reference to Isaiah or Joshua or heliocentrism versus geocentrism. If we remove that assumption (which technically isn’t in the text) then verse 15 is just saying that God moved the earth because that is what God said in verse 13. In other words this has nothing to do with a heliocentric astronomical correction by Mormon or Nephi. It’s purely a thought experiment that if God said to the earth “stop moving” it would appear that the sun stopped.
Now of course this is all quite speculative. Further there may actually be other ways of reading the verses that explain both the earth moving rather than the sun and the “go back” phrase. I just don’t know of any. I just present all of this here as a bit of fun and partially to show that a verse we always thought we understood is a bit more mysterious than it appeared.
 I’m here ignoring whether this actually happened the way it’s presented. There are reasons to be skeptical much as most people read Mormon or Nephi as thinking the text is wrong. The author of these verses in Joshua appears themselves to be quoting something from a now lost Book of Jasher. We don’t have Jasher nor know its textual history. However the text seems a copy of a copy of a text of unknown providence which means we should be cautious. The implications of this actually being massive changes in planetary momentum seem huge which is an additional reason to be skeptical. What matters though is that the author in Helaman (most likely Mormon) appears to be referring to Joshua. In this reading they think the scripture in Joshua is wrong, but mainly because it’s the earth not the sun that moves. (It seems safe to assume they’re ignorant of broad physics)
 Pythagorean astronomy is fascinating as they also had a second earth that orbits of the far side of this central flame but is hidden because of the orbit. This actually becomes influential with the rise of heliocentrism in late Renaissance and early Modernism. Kepler for instance argues the central fire was the sun but the Pythagorians couldn’t actually say that.
 The speeds of planets varies in different astronomy systems. It’s hard not to notice some parallels between the Pythagorean astronomy and Abraham 3. However there are reasons to think Abraham 3 doesn’t refer to the planets viewed in a geocentric system let alone a Pythagorean like system. I should note that some, like John Gee, have argued for a geocentric system for Abraham 3.
 We should be cautious. It appears the Babylonians may have had even more accurate data than the Mayans. But in a certain sense predicting the paths of the planets is not really tied to having a geocentric or heliocentric cosmology. It’s a little known fact that Copernicus’ system didn’t remove the epicycles of Ptolemy’s geocentric system. In fact initially it had more and was more, not less, complicated.