Who needs thermo-imaging?

This picture was taken on January 5, 2021. At first I didn't understand the significance of the melted spot on the top of my hive. This is my double-walled Long Langstroth hive. It has an insulated top cover. Suddenly it dawned on me, this spot is melted from the heat of the cluster beneath it!

This tells me that:

1. My bees are definitely alive

2. The cluster is still located in the front of the hive, so it has a long way to go before using up its stores, and

3. The cluster is of a pretty good size.

Who needs an expensive thermo-imaging camera? My bees told me with no high tech at all!