Fourth of July!

It’s the 4th of July, so I’m celebrating with my American friends.

On this day in 1817, construction began on the Erie Canal in New York state. When completed, it was the second longest canal in the world.

In 1868, Henrietta Swan Leavitt was born. She would go on to discover the period–luminosity relationship for Cepheid variable stars, which provided a way of measuring the universe.

In 1951, Bell Labs and William Shockley announced a successful junction transistor. And in 1997, the Mars Pathfinder (incorporating the Sojourner rover) landed on Mars.

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