Not the same thing and when phenomena are studied they often get additional names

Most of our day-of-the-week names are from the Roman planet-based names, so saturday is saturn-day, and sunday is sun-day. Some names have been changed, e.g mercury-day in english is now wednesday (wodans-day, from the Germanic god Wodan), although in French is it still mercury-day (mercredi).

Emperor Constantine I was the one who, in 321 AD, designated sun-day as a day of rest.

"On the venerable day of the Sun let the magistrates and people residing in cities rest, and let all workshops be closed"