Light from a star is not just a stream but a wave that can oscillate in different directions. Ordinary light is like a crowd where everyone waves their arms randomly. But after reflecting off dust grains or passing through a magnetic field, some waves align in a single line, like soldiers in a row. This alignment is called polarization, and it tells a lot about what the light encountered on its journey.
A new instrument, SQUIDPOL, captures this alignment. It sits on a telescope at the Pyeongchang Observatory in Korea and works like four eyes: light passes through a rotating plate that twists the waves, then splits into four beams. Each beam looks through its own filter grating and sees only waves with a specific tilt. In a single snapshot, the instrument gets four polarization images at once.
But even a good instrument has quirks. A common component, the beamsplitter that directs light in different directions, itself slightly distorts polarization. It's like having a ruler that is slightly bent when you measure an angle. The researchers measured this distortion and learned to subtract it from the data. After the correction, the instrument became accurate to 0.15 percent: that's like noticing a tilt of one-tenth of a degree.
Now SQUIDPOL will look at bright stars whose polarization is already known, and at nebulae where new stars are born. The more precise the instrument, the better we can see the invisible field lines that shape the cosmos. Light again gives away its secrets: you just have to know how to listen.
Polarized light is familiar to everyone: polarized sunglasses block glare from water and glass because they only let through waves of one direction.
In Stanislaw Lem's novel "Solaris," scientists study a mysterious ocean by sending polarized beams toward it, as if trying to read its hidden structure.