@dallin
The Solstices and the Equinoxes are fairly arbitrary dates (handily spread out evenly over the year) but they also sometimes show up on calendars and get mentioned in the news, so there’s a little bit of free advertising thrown in as well.

If, when someone hears that it's the Summer/Winter Solstice or Spring/Autumn Equinox, they think 'Oh yeah, must remember to donate to my favourite projects' then it'd be a nice gentle nudge/reminder.

(I'd like there to be a reference to them :) )