How can we know the shape of the milkyway Galaxy precisely?

Question

As of assuming two very close planets to be one

In: 11

Answer 1

From listening to the radio emissions of neutral hydrogen gas (HI), we can put a map of the gas on the sky.

But, when we investigate the change in frequency of that emission because of the Doppler shift effect, we can get a cross section of relative speed and relative intensity for each of those points.

We can also tell the polarisation of the radio emission as well.

Combining all of these with a bit of lateral thinking, we can get a fairly good model for the overall shape of things.

Then, comparing to the same investigations of other galaxies we can see which of those match closely to our model, and we can get a fairly good educated guess on how accurate our model actually is.

By counting the really faint stars in the sky we can get a duplication of our position with a statistical analysis, that we can get another match with the statistical distribution of globular clusters in the galaxy.

Adding all of these up and comparing, that’s how we see where we are and what the approximate shape appears to be.