Seventh-Day as Sabbath?

Just curious, does anyone else keep Friday sundown through Saturday sundown as the Sabbath?

We don't "keep the sabbath" at those times; but for us Sunday is generally a day of rest or time to visit with family; including attending church. Although with that going on; Saturday is more of a restful day than Sunday is sometimes.

I am Jewish so begin on Friday evening but Saturday is Shabbat for us.

Right now I am no particular religion, but I enjoy studying the Bible. Since God said the seventh day is the Sabbath I try to honor it from Fri sundown to Sat sundown.

I was raised Catholic, went to Catholic schools until High School and I use to go to church every Sunday. (The last 20 years I've been more spiritual than into organized religions) Why isn't it just Sunday? I know the Jewish religion celebrates Saturday as the Sabbath but why do other religions acknowledge Friday and Saturday? What'd I miss?