One of these is clouds, which plague professional astronomers as well the backyard stargazer. Depending on season, sometimes a week or more will be overcast. But clouds do seem to follow astronomers around regardless of the time of the year. And in some cases they bring this upon themselves. Take the case of a large observatory of the past which had terrible observing weather. Five of its directors were named Hale, Gale, Snow, Frost and Rainy! The worst cases of clouds destroying a celestial event involve total solar eclipse. Not only are they relatively rare compared to lunar eclipses but the path of visibility is very narrow (often only 100 miles) and totality last only a matter of minutes. (By contrast, lunar eclipses are visible over the entire nighttime half of the Earth and the spectacle lasts several hours start to finish.) Astronomers (and others) have often traveled halfway around the planet the view a total solar eclipse, only to have it clouded out—sometimes at the very last minute!
The second source of frustration and disappointment is moonlight—bright moonlight, especially around the time of the Full Moon. And it is going to happen again in August! One of the year’s finest and most famous annual displays of shooting stars will be largely washed out this year by our nearest celestial neighbor. Yes, it does happen from time-to time during a major display. But this year’s Perseid Meteor Shower’s peak activity happens on the very same night and at the same time as the Full Moon! Some consolation is the fact that this shower is relatively long-lasting and some Perseid activity runs from July 17th to August 24th. While a fair number of meteors may be seen before and after the maximum, they are no match for the 100 or more shooting stars typically seen at the peak under dark moonless skies!
Former assistant editor at Sky & Telescope magazine & author of 10 books on stargazing. His latest, Celebrating the Universe!, is available from HayHouse.com.