Published online by Cambridge University Press: 25 May 2016
We summarize the past 17 years of our efforts to determine the cosmic abundance of the 3He isotope. The vast majority of our 3He+ observations were made with the NRAO 140 Foot telescope in Green Bank, WV. The 140 Foot ceased operations in July 1999 so that NRAO could prepare to commission its replacement, the Green Bank Telescope (GBT). Our 3He experiment was the last scientific program at the 140 Foot. It is thus poignant and timely for us to reassess the astrophysical context of our 3He results. Here we argue that the existence of “The 3He Plateau” for our sample of simple sources and recent advances in the understanding of the evolution of solar analog stars together suggest that we can finally estimate the primordial abundance of 3He. Our current best estimate for the primordial abundance is 3He/H = (1.5 ±0.6) × 10−5 (s.e.) by number.