בראשית, פרק א׳, פסוק י״ט

The biblical concept of time is fundamentally rooted in the transition from darkness to light, a pattern that establishes the daily schedule for all future generations. A full day is defined as a twenty-four hour period that begins at nightfall and concludes the following night. Because of this foundational structure, Jewish law dictates that the Sabbath and all holidays always begin on the preceding evening [חומש קה ת; ביאורי חסידות].

The fourth day of creation is defined by the formation of the great celestial bodies. Originally, God created the sun and the moon to be entirely equal in size. However, the moon complained about having to share its domain with the sun. In response, God reduced the moon in size. To compensate for this reduction, God allowed the stars to shine alongside the moon to serve as its royal entourage. He also established that a special offering be brought at the start of every new month, serving as a symbolic atonement for diminishing the moon. Furthermore, the moon received a promise that in the future Messianic era, its light will be fully restored to equal the brilliance of the sun [חומש קה ת; ביאורי חסידות].