We see that the origin of the name SUNday comes from the worship of the SUN, moon, and stars (planets). We also see that the second day of the week (MOONday) and the name of the (MOoNth) are named after the second brightest object in the heavens, and that the seventh day of the week (SATURNday) is named after the planet Saturn.
Question 2: What season of the year is attributed to the birth of the SUN?
The following two articles help to pave the way to answering the first question and build a base for answering future questions.