We combine the gravitational-wave measurement of the effective distance to the binary neutron star merger GW170817 , the redshift of its host galaxy NGC 4993 , and the latest Hubble constant measurement from the Dark Energy Survey to constrain the inclination between the orbital angular momentum of the binary and the line of sight to 18 \pm 8 degrees ( less than 28 degrees at 90 % confidence ) .
This provides a complementary constraint on models of potential afterglow observations .