I am trying to build a map that will display what parts of the earth are in daylight and what are dark.

Is that something I can do with an earth file such as
<map name="light_test" type="projected">
<options>
<lighting>true</lighting>
</options>
<image name="readymap_imagery" driver="tms">
<url>
http://readymap.org/readymap/tiles/1.0.0/7/</url>
</image>
</map>
What is the proper way to add the light such as that to the entire map?
Chad H. Glaser
Working with osgearth to implement geospacial realistic simulations