OG wrote:
"Boo" wrote in message
...
Hi,

The question is as the title : given that we see it edge on, then how is
it known that the Milky Way is a spiral galaxy with arms and all ?

Thanks,


The first evidence was provided by Radio astronomy, where radio observations
of atomic Hydrogen wavelengths showed the existence of large scale
structures that could be interpreted as arms. (a rotating disk model allows
us to determine where a body of gas is placed by measuring its relative
speed to us).

I thought that it was determied a spiral by Herschel and his
sister..er..er ..Herschel.