I think we all agree the sun/stars were shining before day 4, though they were not likely visible because of the mist that covered the earth kjv genesis 2:6 before man was yet upon the earth. So it would appear that the sun went nucleur on God's Creation day 1 when he said let their be light, and we all know that plants need sunlight, but didn't need to see, but the animals would need for the atmosphere to be clear, to see, so God moved the heavens and the earth literally to position their spacial relationships in respect to the zodiac, seasons, years, months, and 24 hour days on Creation day 4. Too me this means that Day 4 took a thousand years, etc... When man was created we then have approximately 6,000 years expired since Adams birth, and Adam died less than a thousand years so he died within Gods Day of rest within the creation week day 7. With all this it makes the earth a little older than 12,000 years, but less than 13,000 years since God said let there be light to melt the frozen waters, and to the creation of the atmosphere, the raising up of the earth techtonics so it was lifted out of the waters and in the waters(the waters above and below the firmament), and we all know how God destroyed the earth in the biblical deluge, and how it will again be made new in the jugdment of fire where the elements will be melted with fervent heat, and all things will be made new. Day 4 was important so you could measure time, when God stablished the orbits or the moon, the earth, and thus when Adam was born we have a record of approximaely 6,000 years from his birth, though he died within one of Gods days (kjv genesis 2:17) (kjv genesis 5:5), cause he died less than a thousand years old, and one day to God is as a thousand of our years. With confirmations that one day to God is as a thousand years, it makes the earth since the sun started (kjv genesis 1:3) shining only 12,000 - 13,000 years not 6,000 years ago, and that the earth was void without form before God molded the earth, causing the frozen waters above the face of the waters to melt, when he caused the sun to become a light on Creation day 1, etc...Time became measureable on creation day 4(because God spent a thousand of our years positioning the sun, moon, and the stars in a repetitional orbital planes to give us days, months, seasons, and the zodiac for our knowing the seasons as the earth revolved around the sun), though man wasn't created until God's creation day 6, starting 2,000 years after the beginning of creation day 4. With the clearing of the mist cause of the creation of creatures that needed to see, so the mist was lifted kjv genesis 2:6), and the lights became visible, in the sky on day 4 and it was good, and still is good, etc...
kjv Gen 1:14 And God said, Let there be lights in the firmament of the heaven to divide the day from the night; and let them be for signs, and for seasons, and for days, and years:
kjv Gen 1:15 And let them be for lights in the firmament of the heaven to give light upon the earth: and it was so.
kjv Gen 1:16 And God made two great lights; the greater light to rule the day, and the lesser light to rule the night: he made the stars also.
kjv Gen 1:17 And God set them in the firmament of the heaven to give light upon the earth,
kjv Gen 1:18 And to rule over the day and over the night, and to divide the light from the darkness: and God saw that it was good.