dear prometheus,
as i understand isaiah 30:26 - it says 'ON the day the Lord binds up the fracture of his people.' then it goes on to describe God and his tongue as a consuming fire. basically evil will be burned up. when you compare this scripture to rev. 16:8 says 'and the fourth angel poured out his bowl upon the sun; and it was given to it to scorch men with fire. and men were scorched with fierce heat; and they blasphemed the name of God who has the power over these plagues; and they did not repent, so as to give Him glory...'
so On the day is different than a scorching sun being sustained throughout the milleneum. how could the earth revitalize and allow 'rivers in the desert...rain for the seed...livestock grazing in roomy pasture...
so, on the one hand, you have a great burning - enough that the euphrates river will be completely dried up (rev. 16:12) and the way for the kings of the east to fight with the nations vs. 16 at armaggedon. rev. 17:16 mentions war and weapons as causing the first burning (and will eat her flesh and will burn her up with fire) for God has purposed it in their hearts to execute His purpose by having a common purpose...until the words of God should be fulfilled.
then rev. 18:8 mentions God's own punishment 'paying back double' for the sins of the nations. 'for this reason, in one day her plagues will come, pestilence, mourning, and famine, and she will be burned with fire; for the Lord God who judges her is strong...and the kings of the earth who committed acts of immorality and lived sensuously with her, will weep and lament over her when they see the smoke of her burning.'
so this one world system is going to be basically burned up. vs. 18:18 'and were crying out as they saw the smoke of her burning, saying, 'what city is like the great city.'
i believe the sun will be focused (as God can do whatever he pleases with the focus of the sun) on this area for a DAY. that's all it will take. in one day!
we know after the milleneum that jerusalem will have no need of the sun or moon (rev. 21:23) to shine upon it, for the glory of God will illuminate it, and it's lamp is the Lamb. (so the idea of the sun will be similar to God and Christ the next brightness as a lamp).
rev.22:5 and there shall no longer be any night; and they shall not have need of the light of a lamp nor the light of the sun, because the Lord God shall illumine them; and they shall reign forever and ever.'
so, as i understand it - for A DAY there will be intense heat (enough to divide, as Christ said in the parables, the wheat and the tares by burning). just as Daniel survived the firey furnace, so will christians on that day of intense burning. and the milleneum will probably have the sun and moon at an intensity of just the right proportions to allow the earth to regenerate again for the 1000 years mentioned (where the lion and lamb are peaceful...) 'blessed and holy is the one who has a part in the first ressurrection; over these the second death has no power, but they will be priests of God and of Christ and will reign with him for a thousand years.'
then all will be assumed into spirit as in rev. 21 where there is a new heaven and new earth. the old will pass away.
it's impossible for us to understand all this fully from our perspective. but, the times in which we live - we may well see the sun and moon increase in intensity to a point where it is very uncomfortable. the ozone layer being depleted. and, the part about people blaspheming from the heat has already occurred in many places of the world already. the intensity is becoming way more than it ever has been in the past! we can't survive without God in our physical state.