Happy 17th of July

[StellarVixen]

Why this date in particular you might ask, what's the occasion?

Today is the day when the Calendar (formerly iCal) in Mac OS/macOS is right.

This day happens only once per year.

Until next year! 🥂

 

[NoBoMac]

As to "why", some context, and why World Emoji day is the same:

The date originally referred to the day Apple premiered its iCal calendar application in 2002. The day, July 17, was displayed on the Apple Color Emoji version of the calendar emoji (📅) as an Easter egg.