For comparison , NUMBER@1 Iris never comes closer than NUMBER@2 AU and NUMBER@3 ORGANIZATION@1 never closer than NUMBER@4 AU when it becomes visible to the naked eye in a light pollution-free sky .

For comparison , NUMBER@1 Iris never comes closer than NUMBER@2 AU and NUMBER@3 ORGANIZATION@1 never closer than NUMBER@4 AU when it becomes visible to the naked eye in a pollution-free sky .
