Genesis 1:14-19

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:
And let them be for lights in the firmament of the heaven to give light upon the earth: and it was so.
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.
And God set them in the firmament of the heaven to give light upon the earth,
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.
And the evening and the morning were the fourth day.

On the fourth day of creation week, God created the sun, the moon and the stars.  These creations serve as the physical lights on earth:  the sun to illuminate the day, and the moon and the stars to glow at night.  The sun offers heat during the warmth of the day, while the moon and the stars offer much less heat in the cool of the night.  Not only do they provide heat, but they also serve as the heaven's decoration:  the moon and the stars are beautiful on a clear night; the sunrise and sunset are gorgeous against the horizon.  God's glory is so evident in His creation!  The psalmist said it best:  The heavens declare the glory of God; the firmament sheweth His handywork (Psalm 19:1).  Job acknowledged God's work in creation:  By His breath the skies became fair...(Job 26:13).  

God created a lot in just four days.  Everything that humanity needs for survival has already been created.  Everything that is created after this point is icing on the cake!  God shows His generosity to us in the creation week.  We have so much to be thankful for, and what God did in creation is part of that.  As the Thanksgiving season rapidly approaches, take a moment to give God thanks for what He did during the very first week!