Sunnudagur is named after the sun.
Mánudagur is named after the moon.
Þriðjudagur means "third day."
Miðvikudagur means "middle-of-week day."
Fimmtudagur means "fifth day."
Föstudagur means "day of fasting."
Laugardagur means "pool day" because it was the day of bathing.
They do not. Saturday is named after Saturn, a Roman god. The other days of the week are named after Norse gods.The above applies to the English names of the days. Other languages may have different histories.
In English the seven days of the week are named Sunday, Monday, Tuesday, Wednesday, Thursday, Friday, and Saturday. In Spanish the names of the days of the week are Domingo, Lunes, Martes, Miercoles, Jueves, Viernes, and Sabado They have different names in other languages.
This might be more apparent to speakers of languages other than English. There is a closer match in French, for example. It is not that planets are named after the days of the week. Both the days of the week and the planets are named after various deities that have been influential in human thought over the centuries.
Sunday and Monday are named for the sun and moon. Tuesday, Wednesday, Thursday, and Friday are named for Norse or Germanic deities. Saturday is named for the Roman god Saturn.
The days of the week were named after gods from Norse mythology. For example, Thursday was originally "Thor's day", named after the god Thor.
The days of the week are in part named after Norse gods (and also after the sun and the moon, which are not Norse gods).
In Roman times, the days of the week were named after the 7 visible planets (the Sun and the Moon were in those days considered planets). We have vestiges of this in English: Sunday, Monday, and Saturday are named after the Sun, the Moon, and Saturn. The names of the other four days got modified by replacing the names of four Roman gods with their Teutonic equivalents: Mars -> Tiw, Mercury -> Wotan, Jupiter -> Thor, and Venus -> Frigg/Freyja. It should be fairly obvious how those original names got worn down into the modern versions.
The days of the week are Sunday, Monday, Tuesday, Wednesday, Thursday, Friday and Saturday.
The days of the week in English were mostly named for Norse gods, for example, Thursday = Thor's day. The pattern holds for many of the Germanic languages, too. The Russian week day names are based on a count starting with понедельник (Ponedel'nik) which comes, literally, from "Beginning of the week". In Spanish, you see Roman gods giving their names to the days.
No it was a Romen guy
Not in current usage.
The empty set, if you are referring to names of days of the week.