How bright is Neptune?
The current visual magnitude of Neptune is 7.77. Given its brightness, Neptune should be visible with the help of a binocular with a 30-40mm aperture, easy with a small telescope.
The following chart is the predicted light curve (visual magnitude as a function of time) of Neptune, according to the most recent ephemerides data. Magnitude data is sampled with a 2 days interval and there might be inaccuracies for objects changing brightness very rapidly during the course of a few days. For comets there could be large discrepancies between the observed and predicted brightness because of their highly dynamic behaviour.
Predicted magnitude of Neptune between
January 1600 and December 2499