The psalm for Advent’s first Tuesday is the 72nd. It appears prominently on Epiphany, but we get a daytime preview of it on the third Mass of Advent. What do you make of the cosmology implied in verse 7?
Justice shall flower in his days,
and profound peace, till the moon be no more.
And here, in verse 17a?
May his name be blessed forever;
as long as the sun his name shall remain.
The likely end of the moon will be during the sun’s expansion into the red giant phase. The outer layers of the enlarged sun might slow down our massive satellite enough to spiral into the planet. Or expelled gas from the sun before that final stage might be enough to send the Earth spiraling out just enough to avoid the fate of collision and burning to a cinder.
Psalm 72 has had its interpreters focus on the Messianic aspects, otherwise the notion of a human king ruling till the end of the solar system seems an extreme exaggeration. We know, of course, that the reign of God will extend far beyond the end of the solar system. Planets will be swallowed up, or be ejected from the sun’s vicinity. The sun itself will swell up, then shrink to a white dwarf, and eventually cool to a dark ball of frozen carbon, neon, and oxygen. But grace and faith will remain, those tens of billions of years into the future, and beyond. The psalmist may not have had a glimpse into the ultimate future of the sun and moon, but his lyrical words are no less true.