Throughout your whole life, from the moment you’re born until the moment you die, you will only see seven different days. You will cycle through moody Mondays, hump-day Wednesdays and TGI Fridays over and over again.

But why is this? Who decided on seven days? And where did those names come from?

People have been chopping their weeks up into seven days since the ancient Babylonians – so it’s been a pretty popular structure for 4,000 years or so, and it doesn’t look like it's changing in the near future.

Though the names of the days have gone through a few changes over the last 4,000 years, something has been consistent. Since the time of the ancient Greeks, the days have been named after the celestial bodies: the five known planets and the moon and the sun, which were themselves named after the gods.

The Romans then adopted the system and changed some names accordingly (replacing Greek with Roman gods). Then, when adapting the names into Old English, the Anglo-Saxons sprinkled some of their own flavor into the mix; this is what ultimately gave us the days we know and love today.

Here’s an easy one to start with: the Ancient Greeks deemed a particular day “day of the sun” – hemera helio. After the Latin (dies solis), the Old English word became sunnandæg. Over the years, it evolved into Sunday.

Next up we had “day of the moon” – hemera selenes. In Latin, this became dies lunae. The Old English, however, was monandæg, which eventually left us with Monday.

Now we have some more god-focused names. The following day was given to Ares, the Greek god of war. Then the Romans switched it to Mars, their god of war, and the Saxons did the same with their god, Tiu. Tiu’s day (Old English tiwesdæg) is the reason that we have the name Tuesday.

Hermes, the Greek god of commerce, invention and trickery, got the next day. He was then replaced with Mercury, the Roman god of commerce and science. However, the Saxons decided to go in a slightly different direction. Interestingly, they chose Woden, the violent, insane leader of the “Wild Hunt.” Woden’s day (wodnesdæg) is known as Wednesday.

The Greeks were feeling bold this day and they named it after Zeus, the leader of the gods. The Romans followed suit, giving the day to Jupiter, their supreme god. The old English speakers had a slightly different plan, though; they elected to use their Saxon/Norse god of thunder (and recently hired Avenger), Thor – choosing the name “Thor’s Day” – thursdæg. Fast forward 1,500 years and we’re celebrating (thirsty) Thursdays.

Ancient Greek calendar makers must have loved Fridays as much as we do. They named the day after Aphrodite, the goddess of love and beauty. The Romans’ equivalent goddess is Venus, and the Saxons had Freya. Her day was known as frigadæg, which turned into Friday.

Finally, we have the last remaining day. Cronus, father of Zeus, was given this day. The Romans decided to do their own thing and use their god of agriculture: Saturn. The Saxons must not have been too bothered by this, as they didn’t make a major change. This means that they had sæternesdæg, and we ended up with Saturday.