In English, Tuesday is named for Tiw and Friday for Frig. Monday for the moon, Sunday for the sun, Wednesday for Woden (more commonly known by his Norse name, Odin), and Thursday for Thunor/Thunder (Norse name: Thor).

When your ancestors met mine, they decided Tiw was the equivalent of Mars, Woden of Mercury, Thunor of Jupiter, and Frig of Venus, and hence the correspondence.

https://en.m.wikipedia.org/wiki/Interpretatio_graeca#Interpr...

Sadly, English mythology is now much less well known than Roman, so most people aren’t even aware of these etymologies.

> Sadly, English mythology is now much less well known than Roman, so most people aren’t even aware of these etymologies

In my experience most people aren’t even aware of any etymologies. Or even the word itself.

Spain: "en martes ni te cases ni te embarques" (on Tuesday, don't get married and don't board a ship)

you shouldn't start a business/project either ("...né si dà principio all'arte")

I thought Mars is the god of marriage, and Venus is the god of venturing. It's right there in the name.

According to the OED, the Latin root of “marriage” is of uncertain origin. As far as I’m aware, there’s no known connection to Mars.

No, Mars is the god of war (and the archetype of masculine) and Venus the god of love (archetype of feminine).