I was looking at Wikipedia's article on Justice Potter Stewart and was surprised to read:
On January 20 and 21, 1985, Stewart administered the oath of office for Vice President George H. W. Bush.
(He was Reagan's vice president.) Likewise the Wikipedia article on that inauguration begins:
The second inauguration of Ronald Reagan as President of the United States was held in a small televised ceremony on Sunday, January 20, 1985, at the Grand Foyer of the White House, and was to be repeated the following day, January 21, 1985 at the West Front of the United States Capitol in Washington, D.C., before being moved to the Capitol's rotunda.
It does not, however, explain why there were two oaths administered. Wikipedia's article on the oath of office also lists dual swearings-in for Reagan's second term, as well as for a few other presidential terms, but doesn't give a reason.
I'm particularly curious about Reagan's, because the article quoted above indicates that the first ceremony was "televised" so (a) there's seemingly no point in the second ceremony since everyone there had seen it already and (b) the second ceremony seemingly would be absurd since everyone there would know it was a sham. So why was Reagan sworn in twice for his second term as president?
Note that I'm not asking why there were two celebrations — people like to celebrate. I'm asking why the oath itself was administered twice.