1933

Radio astronomy

• Stars, galaxies, quasars, pulsars, and masers
• emit radio waves, and once we didn’t know it.
• Our instruments were too primitive to detect them.
• We thought the earth’s ionosphere was blocking them.
• Until Karl Guthe Jansky, investigating the source
• of static that interfered with shortwave receptions,
• discovered a signal repeating every sidereal day
• that wasn’t coming from the sun.
• It came from the mysterious heart of our galaxy
• in the constellation of Sagittarius.

Sagittarius A*

• At the center of the Milky Way,
• hidden by clouds of cosmic dust,
• stars and ions orbit a massive black hole.
• We cannot see the thing itself,
• heavy as four million solar masses,
• only emissions from things that orbit it.

Overhearing

• To conduct radio astronomy,
• unlike radar or normal radio,
• we don’t send the signals.
• The universe is full of things,
• wacky and violent,
• sending signals on their own.
• It’s just an accident
• of physics. The universe
• isn’t trying to talk to us.