We in the English-speaking world have been saddled with calling the first day of the week 'sun-day'. We got this name originally from Egyptian astrology which named the days of the week according to which planet (Saturn, Jupiter, Mars, the Sun, Venus, Mercury, and the Moon) was 'dominant' during the first hour of any day of the week (Catholic Encyclopaedia). Rome took up this idea in the first and second centuries (AD) and then the Germanic peoples took the 7-day week but assigned new names for some to fit with their own gods. English has derived its week day names chiefly from this source. Sun-day known as 'the first day of the week' by the Jews (Matt 28.1; Mk 16.2,9; Lu 24.1; Jn 20.1,19; 1 Cor 16.1,2), became known after the Resurrection as the Lord's Day (Acts 20.7; Rev 1.10). Of course, Sabbatarianism disputes the fact that sun-day has become the Lord's Day claiming that the Roman Pope changed the day from the seventh day to the first day. ...
we look not to the things that are seen but to the things that are unseen --Paul, Apostle to the Gentiles