I was walking along the Charles River, when I spotted Professor Daniel Gilbert on his recumbent bike, cruising down a hill toward the Newell Boathouse. He had a broad smile across his face and looked happy, which seemed appropriate since Gilbert studies the science of happiness. He is also the author of “Stumbling on Happiness,” in which he describes the role of “imagination and illusions” in our sometimes misguided pursuit of happiness.

“Human beings are the most social animals on Earth, bar none. So, it is no surprise that our greatest source of happiness is other people. Genuinely investing ourselves in relationships with family, friends, colleagues, and students is the best way to increase our own happiness,”  said Gilbert, in a more detailed email to me.

Echoing this belief was sociology professor Mario Luis Small, who says that casual interactions with acquaintances in our community “offer people a way to be seen, heard, and appreciated, as well as the chance for them to express gratitude. They frequently come free of any expectations. They are likely to be bridges to other communities and networks.”

Within Harvard’s vast community and numerous networks, it was easy to capture moments of sheer joy. Here is a sampling from throughout the school year.