How does St. Thomas propose that angels take part in the creation or direction of heavenly bodies?
Well, in regard to the ‘creation’ of heavenly bodies by angels, St Thomas did not propose such a thing. For him, all heavenly bodies such as the sun, moon, stars, and the body of the heavens itself were created by God. He thought, however, that these bodies were moved by angels either individually such as in the cosmology of Ptolomy who thought that the sun, moon, and stars each had there own motions in the heavens or collectively such as Aristotle thought who thought that the sun, moon, and stars were set in various concentric spheres in which case as the sphere was moved, the objects in the sphere such as stars moved with it. So, an angel either moved a whole sphere in a rotary motion and the objects such as stars in the sphere moved with it though the stars did not themselves move but were set in place in the sphere. Or, as in the Ptolomy scheme, each star or the sun and moon were moved individually in a circular motion as in this scheme each star was not set in place as in the sphere model and which only moved with the motion of the sphere.
St Thomas following Aristotle also considered that the heavenly bodies, the sun, moon, and stars were incorruptible, i.e., made out of a different element which was called the quintessence or fifth element than the corruptible elements of earth, namely, earth, water, air, and fire. However, I think St Thomas considered this more of an opinion rather than of some demonstrative proof because other philosophers had different opinions some believing that the heavenly bodies were made out of the same earthly elements of earth, water, air, and fire, or as Plato thought, the element of fire. He touches upon some of these opinions in his treatise on the work of the second day in the Summa Theologica and actually considers how they all could work in one way or another. From observation, the heavenly bodies do not seem to change except in their motions so we can’t really fault St Thomas for thinking in his time that they may be incorruptible. Indeed, it is said today that red dwarf stars can burn hydrogen for many billions, hundreds of billions and even a trillion or trillions of years before dying out and may in a sense be considered incorruptible as the world I don’t think is going to last that long before the end comes and the second coming of Christ.
Today, we have learned that the heavenly bodies are made out of the same elements that we find on earth and in our own bodies and also that stars die out after a period of fusion burning. The prevailing scientific theory today concerning star formation is essentially that if a certain quantity of hydrogen atoms are gathered together, the force of gravity on this quantity of atoms will eventually result in a star. Other factors and forces are involved which the scientists are continually finding out and which they attempt to incorporate in their models, fudging various factors and forces here and there until a star is born in a computer simulation.
