I learned something the other day that blew my mind. We are now able to take pictures of the far side of the Sun.

How? We could put a telescope in Earth orbit 180 degrees opposite from us. But we don't have one there yet.

We use sound waves.

Sound? In the Sun? Don't you need air for that?

No, any gas will do (solids or liquids too). The Sun is a big ball of very dense gas, perfect for propagating sound waves.

So we image the near side and analyze distortions caused by the sound waves traveling through the Sun. The resulting images of the far side are low resolution, but they are good enough to "see" things like coronal mass ejections and the giant sunspot that rotated into view last week.

https://www.google.com/search?q=solar+sound+waves

https://www.cora.nwra.com/~werne/eos/text/solar_waves_main.h...

https://www.cora.nwra.com/~werne/eos/text/farside.html

https://www.space.com/thanksgiving-sun-sunspot-treat-2020

I wonder if there was a local loudness maximum on the globe diametrically opposed to the volcano. As the advancing wave makes it half-way around the globe, it seems like it would converge simultaneously on a single point on the opposite side.

The RaspberryShake team makes a high-quality "Raspberry Boom" infrasound detector for hobbyists. Next Krakatoa, you can be prepared to detect it yourself. :)

The "RBOOM" sensor alone is $300+, but you can also buy a kit and integrate it into a Raspberry Shake home seismometer setup. I run a RS seismometerat home, but not the infrasound sensor.

"From incoming harsh weather, planes flying overhead, gun fire and nuclear testing, to volcanoes erupting on remote islands in the Pacific Ocean and meteors exploding over the Atlantic… See all these and more. Discover the untold secrets that are out there with your own RBOOM!"

For sale: https://raspberryshake.org/products/raspberry-boom/

Lots more info in the user manual: https://manual.raspberryshake.org/boom.html

(2014)!

previous discussion:

https://news.ycombinator.com/item?id=8383158

https://news.ycombinator.com/item?id=18746225

(2014)