Just to add on to daagh's explanation.
In the given sentence...
The sun and the moon have the same apparent size in the sky -> Main clause
and the other part is the dependent or subordinate clause.
If the Main clause is followed by a subordinate cluase, we have to use a period, a semicolon or one of the following coordinating conjunction.
For
And
Nor
But
Or
Yet
So
And these coordinating conjunction should be followed by a comma.
In the given sentence...
The sun and the moon have the same apparent size in the sky -> Main clause
and the other part is the dependent or subordinate clause.
If the Main clause is followed by a subordinate cluase, we have to use a period, a semicolon or one of the following coordinating conjunction.
For
And
Nor
But
Or
Yet
So
And these coordinating conjunction should be followed by a comma.
