Document #364 in README.md

README.md

@@ -323,6 +323,21 @@ Get the Moon phase for a particular date by adding `@YYYY-MM-DD`:
 
 The Moon phase information uses [pyphoon](https://github.com/chubin/pyphoon) as its backend.
 
+Unicode representation of moonphases suffers 2 caveats:
+
+- With some fonts, the representation `🌘` is ambiguous, for it either seem
+  almost-shadowed or almost-lit, depedending on whether your terminal is in
+  light mode or dark mode. Relying on colored fonts like `noto-fonts` works
+  around this problem.
+
+- The representation `🌘` is also ambiguous, for it means "last quarter" in
+  northern hemisphere, but "first quarter" in souther hemisphere. It also means
+  nothing in tropical zones. This is a limitation that
+  [Unicode](https://www.unicode.org/L2/L2017/17304-moon-var.pdf) is aware about.
+  But it has not been worked around at `wttr.in` yet.
+
+See #364 for corresponding tracking issue. Any help is welcome.
+
 ## Internationalization and localization
 
 wttr.in supports multilingual locations names that can be specified in any language in the world