The English phrase, “day in the sun,” generally refers to long-awaited attention, accolades, or other forms of appreciation. As such, it is usually attached to a pronoun, for example, in “his day in the sun” or “my day in the sun.” It’s often assumed that the positive responses implied in the phrase are deserved, though this is not a given.
Although the phrase “day in the sun” is commonly understood as something more abstract than an actual vacation day, some may refer to the phrase to describe an incentive from an employer that may include vacation time or any other privileges. In common use, the ideas of incentive and broader positive affirmation mingle in the idea of the idiomatic phrase.
When referring to some positive outcome for an individual, the phrase is similar in some ways to another common English idiom: “every dog has its day.” In this variant of the phrase, the idea is that each person deserves his or her own day of appreciation and recognition. Some English speakers understand the phrase “every dog has its day” to mean that even undeserving people may receive attention and accolades at some point, while others take it as a reference to actual canines, many of which are patient and wait a long time for rewards from their owners.
As an idiom, “day in the sun” is sometimes linked to Sunday, generally known in many English-speaking Christian societies as a day of rest. These two ideas may not be very solidly linked in terms of origin, but some English speakers may associate them with one another. The term “Sunday” has its own particular origins, where in a nod to various world religions, the Romans associated the “head day of the week” with the sun. Some Christians later appropriated this as a play on the word “son” in which Jesus Christ figures as the son of God.
Having "a day in the sun" carries an overwhelmingly positive connotation, and is just one of many phrases that regard the sun as a positive symbol of life or happiness. For example, a “sunny day” can be construed by English speakers in many positive ways. The word “sunshine” has also been abstracted into different positive ideas. This general concept is rather important to English and a variety of other world languages.