Calendar: Week of April 21

Here's a look at the week ahead on our "Sunday Morning" Calendar:

Monday sees the 118th running of the Boston Marathon, the first since the bombing last year that killed three people and wounded 260 others.

Tuesday is Earth Day, a day for action to protect the environment, with an emphasis this year on Green Cities.

Wednesday is the ninth anniversary of the first YouTube video, a 19-second clip called "Me at the Zoo," posted by You Tube co-founder Jawed Karim.

Thursday sees the return to competitive swimming of Olympian Michael Phelps, who's entered in three events at the Arena Grand Prix in Mesa, Ariz.

On Friday, Northwestern University's scholarship football players vote on whether to form a union, after getting the green light from a National Labor Relations Board official.

And on Saturday, a section of stage wall from "The Ed Sullivan Show" signed by The Beatles goes up for auction.