What has sunset go to do with Jewish people?

Answer 1

The Jewish calendar is a lunar/solar calendar with a day starting and ending at sunset.

Alternate Answer

Jewish Prayers depend on the hour of the day or night, and the start of a festival or shabbath is at the start of the night (see below). Day is defined as from the first sunray above the horizon till the last ray, i.e. sunset. Night is defined as starting from 3 stars visible in the sky till the first morning light. Hour is 'day' divided in 12 equal parts and is therefore different each day except at the equator.

Since this leaves a undefined gap both in the evening and in the morning (twilight) sometimes the 'night' is considered starting from Sunset, or 'day' starting from first light depending on the stringency of the activity, for example since religious Jews refrain from certain activities on Friday night in order not to violate Shabbath they will start from sunset but keep the restrictions until stars-out, making the Shabbath or festival day actually 25-26 hours (depending on season and location)