A reader writes:
I would like a brief description each of the 9 choirs of angels. Thanks you.
You also might want to read Pseudo-Dionysius's THE CELESTIAL HIERARCHY, which was the work that kicked off the whole nine choirs business.
There's a brief treatment of the subject in THE ARTICLE IN THE CATHOLIC ENCYCLOPEDIA.
And WIKIPEDIA'S ARTICLE may have some useful bits, but it's got a bunch of unreliable junk mixed in, so be careful.
In fact, I'd urge caution regarding the whole idea of nine choirs of angels. This is a highly speculative way of classifying angels and is not part of Church teaching (you will note, for example, that it's not mentioned in the Catechism). The foundations of it are also shaky, biblically. It rests on stitching together several different passages of Scripture and then making the assumptions that the things mentioned in them (1) are all angels and (2) are all different types of angels.
Both of these assumptions are open to challenge.
For example, I am not convinced that there is a difference in kind between an angel and an archangel. The term archangelos in Greek simply indicates a high ranking angel. Archangels may differ from ordinary angels in the same way that high ranking officials differ from low ranking officials or the way that high ranking military officers differ from low ranking military officers. In other words: The difference is one of rank, not of essence.
Indeed, that is what suggested by the very terms. "Angel" in the biblical languages simply means "messenger," with the understanding that the angels are the messengers one would find in God's heavenly court, just as earthly kings have messengers in their courts. In earthly courts, some messengers may hold higher rank than others, but they're all human beings. In the same way, the distinction between a messenger and a high-ranking messenger would seem to be one of rank rather than kind.
When we come to cherubim and seraphim, we're on a little bit firmer ground. These at least look different when they appear in Scripture, though because of the way visionary experience works, I can't rule out the possibility that there is one underlying class of beings behind both, and sometimes it manifests in a way that conveys one visionary impression and sometimes it manifests in a way that conveys another.
Even if we grant that seraphim and cherubim are different from each other, though, that doesn't mean that they are distinct from the choir or choirs of angels and archangels. It might turn out that all angels are either seraphim or cherubim (that there isn't another class). And it might turn out that there are high ranking angels (archangels) among both the seraphim and the cherubim.
So these classes may all co-penetrate each other. They may not be four distinct classes, contrary to assumption (2), above.
When we look at the other five classes--thrones, dominions, principalities, powers, virtues--we're on even shakier ground because it isn't clear from Scripture that these are angelic beings at all. These names are derived from three passages in St. Paul's writings (I'll stick the relevant names after the key terms where it isn't obvious in the English translation):
[God] raised [Christ] from the dead and made him sit at his right hand in the heavenly places, far above all rule [principality] and authority [power] and power [virtue] and dominion, and above every name that is named, not only in this age but also in that which is to come [Eph. 1:20-21].
Finally, be strong in the Lord and in the strength of his might. Put on the whole armor of God, that you may be able to stand against the wiles of the devil. For we are not contending against flesh and blood, but against the principalities, against the powers, against the world rulers of this present darkness, against the spiritual hosts of wickedness in the heavenly places [Eph. 6:10-12].
[Christ] is the image of the invisible God, the first-born of all creation; for in him all things were created, in heaven and on earth, visible and invisible, whether thrones or dominions or principalities or authorities [powers; it's the same word in Greek as in the former passage: exousiai]-- all things were created through him and for him [Col. 1:15-16].
It is not obvious in these passages that Paul is talking about distinct types of angels. That rests on a chain of assumptions that are open to challenge. It is not clear, for example, that he is thinking exclusively of the heavenly realm here. He may have earthly rulers in mind ("in heaven and on earth"), in which case some of these terms may be being used to describe humans. Even if we could identify which terms he's thinking of as referring to spiritual things, he may not be thinking of angels but of Greco-Roman religious concepts that use the same terms (e.g., virtues like Piety were often worshipped as deities, and the Roman emperor and many other rulers were worshipped as well), with the message being that Christ is superior to all of these and that we struggle against them as Christians. Even if we could show that these terms all referred to angels, this still wouldn't show that they are distinct classes of angels, any more than the fact that some humans could be described as principalities and some as powers wouldn't mean that they weren't all humans.
It strikes me as much more likely that Paul is speaking in a generalized way here, piling up near-synonyms that are intended to overlap--and overlap both the earthly and the heavenly spheres--in a way that makes it impossible to use this as a technical listing of different kinds of non-overlapping groups of angels that differ from each other in essence.