A record of the long term variations of the galactic cosmic ray flux can be extracted from Iron meteorites.
Out past Fomalhaut, toward the south galactic pole, the stars fade.
They are produced in the atmosphere by the interaction of galactic cosmic rays with the atoms of the atmosphere.
Radiation could perhaps be a show-stopper because the environment in space - there's galactic cosmic rays.
Why, given its exceedingly smooth beginnings, is the universe so clumpy, on all scales from galaxies to galactic superclusters?
It was possibly the most important observation but it was just personal observation to sample the glory and the majesty of the galactic plain and the centre of the galaxy.
The second are galactic cosmic rays, which, although not as lethal as solar flares, represent a continuous background radiation to which the crew would be exposed.
In fact, the Universe as observed today seems to have barely a fraction of the mass needed to keep galaxies from flying apart, based on the rotations of the stars in the galaxy about the galactic center.
The galactic centre can only be observed at certain wavelengths, such as X-rays, because large amounts of dust lie in our line of sight and this blocks out optical light.
By contrast, to reach our nearest galactic neighbor, the Andromeda galaxy, you'd need only twenty-five Milky Ways.