My favourite part:

> In 2016, the hosts of episode #561 of The Skeptics' Guide to the Universe podcast read a letter forwarded by a member of the Carter family from Carl G. "Jere" Justus, giving his explanation of Carter's UFO sighting:[12]

After recently reading the book Georgia Myths & Legends, by Augusta Chronicle columnist Don Rhodes, specifically Chapter 5, "Jimmy Carter and the UFO", I am virtually certain that I have identified the source of what it was that President Carter saw. In the 1960s and early 70s, I worked on an Air Force sponsored project that studied the upper atmosphere using releases of glowing chemical clouds, produced by rockets launched from Eglin AFB rocket range in Florida. Some of these chemical clouds, notably sodium and barium, were visible by the process of resonance scattering of sunlight. Clouds of this type had to be launched not long after sunset or not long before sunrise. This was due to the fact that the cloud had to be in sunlight at high altitude, while it was still dark enough at ground level for the cloud to be visible against the dark sky. In Carter's official 1973 UFO report, as given in the Rhodes book, he stated that he had seen the phenomenon in October, 1969, at 7:15 pm EST. However, it has been determined from Lions Club records that Carter must have seen the "UFO" when he spoke to their Leary, GA Chapter on January 6, 1969. The report "U.S. Space Science Program Report to COSPAR, 1970" (QB504.U54, Appendix I, page 154) documents that there was a barium cloud launched from Eglin AFB (Rocket Number AG7.626) and released on January 6, 1969 at 7:35 pm EST (January 7, 1969, 0035 UTC) [COSPAR stands for Committee on Space Research]. The reported altitude for this cloud was 152 km. With a distance between Leary, GA and Eglin AFB, FL of about 234 km, this cloud would have appeared in the sky at an elevation of 33 degrees (consistent with Carter's estimate of a 30 degree elevation). Carter's report notes that stars were visible, so the night must have been clear. I can verify from personal experience that under clear skies, a barium cloud such as this would easily have been visible from the distance of Leary, GA. Carter reported the UFO "appeared from West". The direction of Eglin AFB from Leary, GA is approximately WSW. Thus this barium cloud at Eglin is consistent with Carter's reported "UFO" as to time, elevation, and direction. Furthermore, the appearance reported by Carter is totally consistent with a high-altitude barium cloud. His report stated that it was "bluish at first, then reddish, luminous, not solid". A neutral barium cloud would initially glow bluish or greenish, with parts of it taking on a reddish glow as some of the barium becomes ionized in the high altitude sunlight. The size and brightness, reported as being about that of the moon, would also be consistent with a barium cloud at Eglin, as viewed from Leary, GA. Carter has been reported as saying that he never believed that he had seen an alien spacecraft, but that he had no idea exactly what it was. I'm interested in exploring if this information could be relayed to President Carter, so that if he wishes to, he can better understand what it was that he saw back then.