Please help me with this Node.

Hello I’m new to blender(and this site so I’m sorry if i posted this in the wrong place).
I was doing a tutorial I found on creating Earth in blender (http://blenderartists.org/forum/showthread.php?t=132869) and when i got to the nodes and page 8 in the tutorial there was a node which I’m not sure how to get.Its the node that’s connected to the the top most Screen node. All it says is “Sh”(the rest is cut off) for the title and it has a little value panel that says ac 0.10. Any clue to what this node is?
Thanks :slight_smile: