Do something with the calendar in the task bar Linux

So, you have this Date/Time thing in the taskbar of Gnome and you'd like to see it do ... something more than simply display a calendar. Have you double-clicked on a date yet? Evolution pops up. You probably don't need it to be your mail client, but by default, it's the interface to show calendar information (whether a Date is bold or not) in that applet.

Certainly, you can use the built-in calendar, but Evolution allows you to use web calendars (such as Google Calendar) as well.

How simple is it?

If you're in Evolution, make sure you're in "Calendars" mode.
Right-click on the white box above the calendar and choose "New Calendar". Sure, you can use the Google link to do it, and it'll be easy to choose your calendars. But if you have the direct URL to a .ics file, change the "Type" to "On The Web". Give it a name, color, and paste the link in the URL box, but change http to webcal.

The following is the public .ics for the USA holiday calendar. Copy/paste it into the URL box.
webcal://www.google.com/calendar/ical/usa__en%40holiday.calendar.google.com/public/basic.ics

This is the phases of the moon:
webcal://www.google.com/calendar/ical/ht3jlfaac5lfd6263ulfh4tql8%40group.calendar.google.com/public/basic.ics