  In recent years, the autocorrelation of the hydrogen Lyman-{\alpha} forest
has been used to observe the baryon acoustic peak at redshift 2 < z < 3.5 using
tens of thousands of QSO spectra from the BOSS survey. However, the
interstellar medium of the Milky-Way introduces absorption lines into the
spectrum of any extragalactic source. These lines, while weak and undetectable
in a single BOSS spectrum, could potentially bias the cosmological signal. In
order to examine this, we generate absorption line maps by stacking over a
million spectra of galaxies and QSOs. We find that the systematics introduced
are too small to affect the current accuracy of the baryon acoustic peak, but
might be relevant to future surveys such as the Dark Energy Spectroscopic
Instrument (DESI). We outline a method to account for this with future
datasets.
