The Union Jack flag is constructed from the Saltire of St Andrew for Scotland and St Patrick for Ireland—a saltire is the heraldic name for the diagonal cross-look—together with the cross of St George for the Kingdom of England. As Wales was a principality, not a kingdom, at the time the flag was created, it is not represented in the design.

Before Ireland’s emblem was added, there was actually an earlier flag back in 1606— the first Union Flag — with just Scotland and England present.

The Flag Institute explains why it's called a "jack"

Someone who studies flags is called a vexillologist, as I'm sure you know.

Curious about the difference between Great Britain, the United Kingdom and the British Isles?

The Union Jack

I like this radius. It explains some of why asteroids are lumpy and bumpy, kind of like potatoes, and yet planets and moons are smooth round balls.

From the potato radius size, about 2–300km, the mass of the rock itself gets large enough that it is pulled in on its own gravity and consequently starts to round itself off.

I learned about this from Brian Cox’s show Forces of Nature.

Not sure about asteroids, meteors and meteorites?

The potato radius

This is generally the source of much confusion. Even amongst those who live over here. If you look carefully at the description of the United Kingdom, you’ll see it’s the United Kingdom of Great Britain and Northern Ireland. And the British Isles is the group of islands as a whole, including all of Ireland too.

The source I liked best for this explaining this and much more was Project Britain.

For much further confusion, think for a moment why there’s a UK passport, Great Britain in the Olympic games, and in football, we compete as England, Wales, Scotland and N. Ireland separately. 🤔

You might be interested in the Union Jack: The making of a flag

Get my new weekly sketch in your inbox

Great Britain, the United Kingdom and the British Isles: what’s the difference?