ent ▁Calendar . ▁The ▁SET I ▁e cli ptic ▁search ▁idea ▁suggests ▁foc using ▁SET I ▁efforts ▁in ▁the ▁e cli ptic ▁plane ▁in ▁which ▁distant ▁hypoth et ical ▁obser vers ▁can ▁see ▁the ▁Earth ' s ▁trans it ▁of ▁the ▁sun . ▁The ▁Han ke - Hen ry ▁P erman ent ▁Calendar ▁is ▁one ▁in ▁which ▁the ▁number ▁of ▁days ▁in ▁a ▁year ▁is ▁always ▁divis ible ▁by ▁seven , ▁such ▁that ▁hol id ays ▁always ▁fall ▁on ▁the ▁same ▁day ▁of ▁the ▁week . ▁Most ▁years ▁have ▁only ▁four ▁qu arters ▁of ▁ 9 1   days , ▁while ▁every ▁five ▁or ▁six ▁years ▁an ▁extra ▁week ▁is ▁inserted ▁at ▁the ▁end ▁of ▁December . ▁ ▁He ▁is ▁also ▁active ▁in ▁various ▁organizations , ▁including ▁the ▁Stre it ▁Council ▁where ▁as ▁of ▁ 2 0 1 2 ▁he ▁is ▁president ; ▁the ▁Maryland ▁Space ▁Grant ▁Cons ort ium ; ▁and ▁an ▁organization ▁he ▁founded , ▁the ▁Henry ▁Foundation , ▁which ▁" sp ons ors ▁improved ▁world wide ▁understanding ▁of ▁physics ". ▁He ▁earned ▁a ▁ ▁Ph . D . ▁from ▁Pr inc eton ▁University ▁in ▁ 1 9 6 7 . ▁ ▁He ▁is ▁c ited ▁for ▁providing , ▁for ▁black ▁holes ▁that ▁are ▁rot ating , ▁and / or ▁are ▁elect r ically - charg ed , ▁the ▁K ret sch mann ▁scalar , ▁which ▁character izes ▁their ▁degree ▁of ▁curv ature . ▁ ▁References ▁ ▁Further ▁reading ▁▁ ▁Category : J oh ns ▁Hop kins ▁University ▁fac ulty ▁Category