If you’re doing an Advent calendar this month, you’re just over halfway finished opening up those little windows to see what’s inside.

So let’s open up a few windows into where these calendars came from.

We wouldn’t have Advent calendars, of course, without Advent.

It started in the 4th Century as a four-week lead-up to the Christian feast of Epiphany in January; later it was associated with Christmas in December.

Technically Advent is structured around the four Sundays leading up to Christmas Day, but the calendars generally just run from December 1-25.

Pretty much anyone who’s excited about Christmas has kept a countdown of sorts.

And there are lots of different ways to count down; growing up, my siblings and I would make those construction paper chains and then undo a link each day leading up to the holiday.

Since Advent calendars are essentially countdowns, I think they should come with Casey Kasem-style long distance dedications.

Anyway, the Advent calendar we know today started in Germany.

In the 19th Century, German Protestants would make chalk marks on a door, light candles, or place pieces of straw in the crib of a Nativity scene in the days leading to Christmas.

In the very early 20th Century, several printers offered images where kids could follow along through Advent.

One of them, Gerhard Lang, created a range of interactive calendars, including ones with little windows kids could open.

Over time this style Advent calendar became the standard; people would open up the windows to find illustrations, Bible verses or even little toys or candies.

Advent calendars went into hibernation during World War II, when paper was rationed.

But after the war, they really took off; President Dwight Eisenhower had one at the White House, and chocolate companies, among others, realized there was a lot of money to be made with the Advent calendar as a holiday tradition.

Today you can get just about any kind of Advent calendar you want, with candy, or coffee or adult beverages inside; there are non-Advent Advent calendars that count down to Hanukkah, and there are Advent calendars that give you exercises to do each day, so you burn calories ahead of the holidays.

I know we’re now closer to the end of the season than the beginning, but I’m not gonna stop anybody from getting me the Advent calendar that lets you build your own pinball machine.

Engineering students at ETH Zurich have a real challenge ahead of them.

Teams are designing small robots which have to successfully drop a series of very small gifts down scale model chimneys.

The top ten teams meet in the finals on December 17th.

Do the robots get to have teams of little drones to serve as their reindeer?

Advent calendars, explained: Where they came from and why they’re everywhere now (NPR)

Robots help deliver gifts (ETH Zurich)

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Photo by henry… via Flickr/Creative Commons