I found this ol aircheck of WGBH on YouTube from March of 1987 (the month and year I was born!)

The visual look for NOVA promos of a squeezed screen against a NOVA logo and the episode of interest had apparently been introduced in the 1986-1987 season, with a plain backdrop, more plainer than seen below.

That reason may be because the open dated from the start of the 80s and and the CGI open designed from NY Institute of Tech wasn’t really flexible other than the open

In the 1988-1989 season, did the Big-Bang looking purple aura became NOVA open and as seen below, a still of that was used in promos for a number of years well into the mid 1990s (I posted this one!)