The recurrent nova T CrB did not erupt in the year 1842
The recurrent nova T CrB was one of the first well-observed nova eruptions, in 1866, and 80 years later it erupted again, in 1946. Just after the 1866 eruption, Sir John Herschel reported to the Monthly Notices that he had seen the same star in his naked-eye charting of the sky on 1842 June 9, implying that there was a prior eruption 24 years earlier. Unfortunately, the chart in the Monthly Notices was ambiguous and misleading, so it has long been unclear whether T CrB did indeed have an eruption in 1842. To resolve this, I have searched the various archives containing Herschel material, and have found his original correspondence. In one letter from 1866 to William Huggins, Herschel enclosed his own copy of his original observations, and with this all the ambiguities are resolved. It turns out that Herschel's indicated star was at the same position as a steady background star (BD +25° 3020, V = 7 m.06, G8V) and not that of T CrB, and Herschel regularly was seeing stars as faint as V = 7m.5 because he was using an opera glass. With this, there is no evidence for a T CrB eruption in 1842.
Publication Source (Journal or Book title)
Schaefer, B. (2013). The recurrent nova T CrB did not erupt in the year 1842. Observatory, 133 (1233), 81-88. Retrieved from https://digitalcommons.lsu.edu/physics_astronomy_pubs/4661