Hydrogen detection 3 spiral arms of the Milky Way (Deneb)
One of the most startling measurements was the discovery of the spiral arms of the Milky Way. For example, if the dish is pointed towards the star Deneb, the following graph is created.
We see 3 times a hydrogen line detection with a small difference in frequency and intensity. This has to do with the Doppler shift of the 3 signals. Our own arm in which we (our solar system) are located is exactly 1420.405 MHz.
But the emission of hydrogen from the 2 other arms is also detected by the dish. These arms rotate around the core at the same speed as the Sun. By the way, you would expect the outer regions to spin slower than the core (just like a vortex). However, this turns out not to be the case, which can also be measured with my radio telescope. It to do with measurements of the rotation curve of the Milky Way showing that there is dark matter