What's the plural form of southern solstice? Here's the word you're looking for.
Answer
The noun southern solstice can be countable or uncountable.
In more general, commonly used, contexts, the plural form will also be southern solstice.
However, in more specific contexts, the plural form can also be southern solstices e.g. in reference to various types of southern solstices
or a collection of southern solstices.