Vacation locations for some months prior to perihelion and remained visible for a total of at least months. Even though its peak magnitude was it remained brighter than magnitude for some weeks, the longest of any comet on record. Generally, you can calculate a comet’s apparent magnitude if you know its absolute magnitude intrinsic brightness and its location with respect to the Sun and Earth. However, comet brightness is not always predictable. Comets may underperform. Some new comets, like Comet Kohoutek of and Comet ISON of , promise to be magniicent when irst observed but end up failing to live up to expectations. When irst discovered, many astronomers predicted that at perihelion ISON would be one of the most glorious comets in human history not only would it have an apparent magnitude of but it would also put on a spectacular, once-in-a-millennium show for Earth’s inhabitants. Vacation locations 2016.