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Look at the stars and you are looking back in time. Because light takes many years to travel the vast distances between stars, we see them not how they are now, but how they were decades or centuries ago.
And that allows us to have a bit of fun with star charts.
We've put together maps of three well-known star groups, each visible even through London's light-polluted skies. We've labelled each star with a historic London event roughly corresponding to the age of the starlight.
So, Betelgeuse, the famous star on the left shoulder of Orion, is 548 light years away. The light reaching us from the star today (newsworthy for its recent dimming) set off 548 years ago in 1475... roughly the same time as William Caxton was setting up the first London press, in Westminster. And we can do the same for the other stars.
Here's how it looks for the Plough/Big Dipper...
Plotting history against the stars lets us see them in another dimension. We might unthinkingly imagine that the stars of Orion or the Plough are all at roughly the same distance, but that's not the case. The stars in Orion vary from 250 to 1350 light years away — a fact that becomes more obvious when we pin historical events next to them.
We can also see immediately that the stars of the Plough (above) are all much closer than those of Orion. The light from all seven of its stars began its journey to Earth in the 20th century.
Finally, the "W" shaped constellation of Cassiopeia. Its star light spans from the Battle of Barnet to the Swinging Sixties.
We've focussed on London history here because... well, we're Londonist. But you could make up your own star charts for world history, or the chronology of your own home town. It's an intuitive way to get a better handle on the cosmos — and would make a fun project for kids.
Note: Light year distances are approximate, and corresponding historical events may be a year or two either side. The events labelled against each star were chosen in 2023. As time goes on, they'll need updating.
