“Sing for joy, O heavens, for the Lord has done this; shout aloud, O earth beneath. Burst into song, you mountains, you forests and all your trees, for the Lord has redeemed Jacob, he displays his glory in Israel”. 
Isa 44:23 NIV 

In World War II a large company of South African soldiers were taken prisoner of war in the North African campaign. The conditions in their camp were atrocious and illness was rife, there was almost no food and water was scarce. Some were on the point of death and most were losing hope. The doctor had no medical supplies and eventually said, “Go to the padre and get him to pray for you. There’s nothing more I can do”. The padre had a fine singing voice and gathered them all together. He got them to sing some of the hymns they had learnt in Sunday School and at church. Those who survived said afterwards, “It was the padre’s hymns that saved our lives. They lifted our spirits, turned us to God, and gave us hope and faith”. 
Maybe the prophet Isaiah had a similar effect with the exiles in Babylon. Whether the exiles thought there was anything to sing about or not, we do not know. Isaiah, who was probably remembering a psalm from the temple, struck the right note. In the darkest days – sing for joy, it will lighten the darkness! He called on nature to sing. Probably the exiles, or some of them, joined in. 
When your sun has gone out and the darkness is descending around you, sing for joy as well. Get others to sing with you, or join them in song and praise. See if you too can see God displaying his glory in all the world around you. 

Lord, help me to praise you in the darkest night.