Happy #BlackHoleWeek to those who celebrate! Here's a pic I took a few years ago back when I worked at ESO's Paranal Observatory in #Chile. One of our 8.2 m telescopes was pointing at the centre of the #MilkyWay, home to Sagittarius A*, a #BlackHole 4 million times more massive than the #Sun.
Astronomers devoted almost a century to unmask this beast:
@DelRider The laser excites sodium atoms in a layer 80-90 km above the ground, making them glow. This creates an artificial "star" that we can use to monitor atmospheric turbulence in real time, correcting it with a fast deformable mirror.
EDIT: forgot to mention that it's yellowish because it has a wavelength of 589 nanometres, chosen to excite those sodium atoms.
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