The bulk of this material seems to consist of two types: Hot blue masses of highly radioactive r -process matter of lower-mass-range heavy nuclei (A < 140) and cooler red masses of higher mass-number r -process nuclei (A > 140) rich in actinides (such as uranium, thorium, californium etc.). When released from the huge internal pressure of the neutron star, this neutron-rich spherical ejecta expands and radiates detected optical light for about a week. Such duration of luminosity would not be possible without heating by internal radioactive decay, which is provided by r -process nuclei near their waiting points. Two distinct mass regions (A < 140 and A > 140) for the r -process yields have been known since the first time dependent calculations of the r -process. Because of these spectroscopic features it has been argued that r -process nucleosynthesis in the Milky Way may have been primarily ejecta from neutron-star mergers rather than from supernovae.