This is the spring equinox. An equinox is when day and night are at equal lengths. It usually takes place in March, and marks the beginning of spring in the northern hemisphere.
Life is beginning to "spring" into gear, so to speak. Flowers are blooming, the weather is warming up, and people - in the past, at least - are celebrating that they made it through winter with whatever they had. Hooray! Also, more hours of daylight are coming, which is a plus.