<P> The controversy was conclusively settled by Edwin Hubble in the early 1920s using the Mount Wilson observatory 2.5 m (100 in) Hooker telescope . With the light - gathering power of this new telescope, he was able to produce astronomical photographs that resolved the outer parts of some spiral nebulae as collections of individual stars . He was also able to identify some Cepheid variables that he could use as a benchmark to estimate the distance to the nebulae . He found that the Andromeda Nebula is 275,000 parsecs from the Sun, far too distant to be part of the Milky Way . </P> <P> The ESA spacecraft Gaia provides distance estimates by determining the parallax of a billion stars and is mapping the Milky Way with four planned releases of maps in 2022 . </P>

In which of the following ways are the bulge and halo of the milky way most similar