add a public Google calendar to your Android device

Subscribing to a Google calendar on Android is actually a two-step process. You must first subscribe to the calendar using the web version of Google Calendar and then add it to your Android device.
Subscribing to ical on Google Calendar web:
Step 1: go to Google Calendar on the web
Step 2: Choose "Other calendars"
Step 3: In the dropdown menu, choose "Add by URL"
Step 4: Insert our calendar's ical address in the URL box and click "Add Calendar." Now you should be able to see our calendar in your Google calendar. 

Adding subscribed calendars to Android:
Step 1: On your Android device, you may have to clear the existing calendars and re-sync the data for a new calendar to show up.
  • Settings / Applications / Manage Applications / Calendar -> Clear Data
  • then Settings / Applications / Manage Applications / Calendar Storage -> Clear Data
Wait a few minutes and you should be able to see the new calendar. If the new calendar does not show up, also do the following:
  • Settings / Accounts & sync -> select your account, uncheck the "Sync Calendar" option 
  • Wait a few minutes and re-check the Sync Calendar option to see
Keep in mind that if you have 2-step verification enabled on your phone, you may have to remove the account entirely and re-add it.