Google doodles for the longest day of the year, northern hemispherically speaking. June 21st is summer solstice in the northern hemisphere (winter solstice in the south), and is the period of longest daylight. The sun's reached it's northernmost zenith at the Tropic of Cancer. Many cultures around the world recognize solstice with rituals, holidays, festivities and other traditions, as it's seen as a time of fertility.
A Murakami for the start of summer in the northern hemisphere
The Doodle itself is a sketch by Tokyo artist, Takashi Murakami. His style of art is called “superflat” and is derived from anime and manga. In addition to today's Google Doodle, other Murakami works have included the albumwork for Kanye West's album, “Graduation” and he's had an exhibition of his artwork at the Palace of Versailles in France, where he filled up 15 rooms with his sculptures.