They are parallel in the passage. "Shouting for joy" parallels "sang in chorus," and "the sons of God" parallel the "morning stars." (Just for the record here, I don't believe stars are literally divine beings/angels). This is typical parallelism found throughout Hebrew poetry. Not only is the parallelism pretty obvious, but in Ancient Near Eastern cosmology, the stars were often thought of as some sort of semi-divine beings. There are other places in the bible as well (though admittedly not many) that suggest this sort of cosmology:
Is
14:13 You said to yourself,[SUP]
[/SUP]“I will climb up to the sky.
Above the stars of El[SUP]
[/SUP]I will set up my throne.
I will rule on the mountain of assembly
on the remote slopes of Zaphon.
The claim of the king of Babylon in Isaiah 14 is that he was equal with God. Verse 14 makes sense within this context when it's understood that the stars of El were thought to be some sort of divine beings, and that the King of Babylon would set himself up over them - as in rule over them.
It shows up again in Job as well. The parallelism is easy to spot:
Job
15:15 If God places no trust in his holy ones,[SUP]
[/SUP]if even the heavens are not pure in his eyes,
And here again in 25:
25:4 How then can a human being be righteous before God?
How can one born of a woman be pure?
25:5 If even the moon is not bright,
and the stars are not pure as far as he is concerned,[SUP]
[/SUP]
25:6 how much less a mortal man, who is but a maggot –
a son of man, who is only a worm!”
If it's understood within the framework of ancient near eastern cosmology, the argument makes perfect sense. If even the divine beings aren't righteous, how can a human possibly be righteous? It makes no sense if he's talking about inanimate conglomerations of rocks and gas. The argument wouldn't even function to be understandable if it were saying: how can a human being be righteous if the gaseous objects in the sky aren't righteous. Well, I don't think literal stars and planets can be righteous or unrighteous given that they are rocks and gas. But if you understand the cosmological framework Job and his friends are operating in, then it's easily understandable.
I'm only saying this because it was previously said that those Christians who take Job to be just "Wisdom Literature" are wrong and should take it literally. My counter argument, since I fall in that category, is that if you're going to take it literally, you have to go whole-hog and say that the stars, planets and heavenly bodies are literally divine beings.