How often do bright optical transients occur on the sky but go unreported? Toconstrain the bright end of the astronomical transient function, a systematicsearch for transients that become bright enough to be noticed by the unaidedeye was conducted using the all-sky monitors of the Night Sky Live network. Twofisheye continuous cameras (CONCAMs) operating over three years created a database that was searched for transients that appeared in time-contiguous CCDframes. Although a single candidate transient was found (Nemiroff and Shamir2006), the lack of more transients is used here to deduce upper limits to thegeneral frequency of bright transients. To be detected, a transient must haveincreased by over three visual magnitudes to become brighter than visualmagnitude 5.5 on the time scale of minutes to years. It is concluded that, onthe average, fewer than 0.0040 ($t_{dur} / 60$ seconds) transients withduration $t_{dur}$ between minutes and hours, occur anywhere on the sky at anyone time. For transients on the order of months to years, fewer than 160($t_{dur} / 1$ year) occur, while for transients on the order of years tomillennia, fewer than 50 ($t_{dur}/1$ year)$^2$ occur.
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