This star is 39.5884 parsecs away (129.12 light years). Although the light from ξ Herculis is slightly diminished by the intersteller dust between it and us, it it still bright enough to be visible from earth to the naked eye.
ξ Herculis is a well studied star and it is mentioned in over fifty scientific publications. The earlist reference to ξ Her listed in SIMBAD is the paper titled "Radial velocities of 99 stars of the second and third spectral classes observed at Bonn." by F. Küstner which was published in the June 1908 edition of the Astrophysical Journal.