The moon is round because its not flat.

1. First statement: "The moon is round because its not flat"
   If “because” is replaced with a phrase like, “in other words”, then it is a deliberate clarification and not a fallacy. Only here, that's not the case. Here it was expressed as an explanation. That's the limited scope fallacy.


2. Second Statement: "The planets are all round because otherwise they wouldn't be able to go around each other" That's like saying "ONLY round objects can be planets" and then you asked "why are all planets round" = "why can't flat objects be planets" and the answer was "because flat objects can't be planets" which again, instead of providing an explanation, it's rephrasing the phenomenon, so that's again limited scope. 

Strictly speaking, there is no logical fallacy here because the argument is trivially valid - a tautology that takes this form:
x is x because it is not non-x
On the other hand, you will probably agree that what is to be argued here is only assumed in some way, so we can consider this as begging the question .
This is also an example of a bad explanation. The explanation and the argument are not the same, and an explanation is often sought in response to the “why” question

I assume by ""round" they mean "spherical." But perhaps I'm being charitable.😒

Hi, Jason!

         Someone you asked argued, "the moon is round because its not flat.”

         This is a non sequitur. Being a non-flat object does not entail being a round object.  A cube is not flat, but neither is a cube round.

         Some people might have thought that the argument was trivially valid. However, these people are mistakenly supposing that the attributes of being round and being flat are contradictory, like being x and being non-x. Being round and being flat are not contradictory. Consider the fact that cubes are neither round nor flat, which would not be possible if roundness and flatness were contradictory attributes.

         Since there is the possibility for an object to be neither round nor flat, it is not valid, let alone trivially valid, to infer that an object is round just because it is not flat. The argument is a non sequitur.

         The person continued to argue, “the planets are all round because they wouldn't be able to go around each other if they were all flat and could not go around if they were not round.”

         This is essentially what the argument states, as it is presented:

1.       The planets would not be able to go around each other if they were all flat.

2.       The planets could not go around each other if they were not round.

3.       Therefore, the planets are all round.

         The planets do go around each other is likely an implicit premise of the argument. So, I am going to add it. However, this implicit premise together with premise 1 entails that the planets are not all flat . In light of this, the argument seems to also contain the implicit conclusion that the planets are not all flat. Hence, here is my full reformulation of the argument:

1.       If the planets were flat, then they would not be able to go around each other.

2.       If the planets were not round, then they could not go around each other.

3.       The planets do go around each other.

4.       Therefore, the planets are not flat.

5.       Therefore, the planets are round.

         Notice that statement 3 is the tacit statement that I added. Notice that statement 4 is the conclusion which the arguer did not give, but which nonetheless follows from his tacit statement together with premise 1.

         What confuses me is the relationship between 4 and 5. I am tempted to think that 4 is an intermediate conclusion and that 5 is intended to be the main conclusion, inferred directly from 4. After all, the moon argument was treated the same way. Recall that the arguer immediately inferred that the moon is round because it is not flat. In light of the precedent set by the moon argument, I think 4 is an intermediate conclusion from which 5 is immediately derived. Just like we saw with the moon argument, this inference from 4 to 5 makes the planet argument a non sequitur. (5 still follows from the argument, though. Notice that it follows from 2 and 3.)

         On the other hand, if the arguer insists on 4 and 5 as independent main conclusions, he can escape the charge of a non sequitur where 4 and 5 are concerned.

Thank you, Jason.

From, Kaiden