"And God said, '"Let there be an expanse in the midst of the waters, and let it separate the waters from the waters."' And God made the expanse and separated the waters that were under the expanse from the waters that were above the expanse. And it was so. And God called the expanse Heaven. And there was evening and there was morning, the second day."
This is the Biblical account of the second day of the world's creation. This was the day that God made sky. He made the heavens. This is the day that there became a separation between sky and earth, the day that birds had a place to fly and the day that space and open skies became a reality.
The day that God made the Heavens must've been beautiful. It would've been the day that hosted the first sunrise and the first sunset, the day that made cloud watching possible and the day that gave way to the great expanse of sky that wraps around the entire world. He separated clouds from lakes and storms from oceans, all with the command of His voice.
That was the second day.
-Cliff
Cliff's Note: The first sunrise and sunset must've been special; it was the beginning of the sky's worship toward the Heavens.