Heuer produced two very different versions of the Solunar -- the first version was introduced in 1949 and the second version was introduced in 1976. For an overview of the two models, see the Calibre11.com posting Series Overview: Heuer Solunar.
For information about the Solunars from the 1950s, have a look at this article introducing the watch and this Instruction Booklet. For information about the Solunar from the 1980s, have a look at this Instruction Booklet.