Confusion surrounded the recent meteor shower: Many TV stations said that the Perseids would peak on Monday night, August 12. Sources such as Astronomy magazine and Almanac Weekly correctly pegged Sunday night as the best time to observe them.
Well, it was Sunday night. At Mohonk Mountain House, our excited crowd of 350 people, stretched out on blankets and towels in a rec field, counted ten bright meteors in a half-hour period around 9:30 p.m. Intrepid insomniacs who ventured out later reported about one a minute in the hours before down.
By my own count, the next night, Monday night, showed only about one-fourth that number. Monday night was a bust.
What went wrong? First, NASA had announced that the meteors would peak on Monday. And this was true, in a way. The peak hour was 2 p.m. EDT, Monday afternoon. Who could blame any TV station for thinking that the shower would thus be best on Monday night?
But the Perseids, which begin in late July, slowly rise in number and then fall off rapidly after their peak. The night before the peak is always much better than the night after. NASA should have mentioned this fact in its press release, but didn’t.
Moreover, Perseids are always best the second half of the night. So their maximum happened in the wee hours of Monday morning, meaning Sunday night.
Actually, the second half of every night is a different animal from the first. At sunrise your position on Earth has rotated to a spot facing the forward direction in which our planet moves through space. That’s when our planet plows through bits of ice or stony metal; whereas meteoroids must catch up to us from behind during the night’s early hours. So of course we see more after midnight.
Another post-midnight difference is that the hours before dawn are home to the Last Quarter Moon: the lunar phase lit up on the left. That’s the phase that we’ll see this coming week. It’s not even visible the first hours after sunset. By contrast, the evening half of the night is when the First Quarter Moon is out: the Moon lit up on the right.
So again, the night’s two halves always offer different phenomena. We’ve got an abundance of post-midnight meteors: an average of six an hour even on non-shower nights. We see darker skies, thanks to many malls automatically turning off a percentage of their parking lot lamps then, creating less light reflected skyward.
And finally, unlike some primitive calendars, our days begin at midnight. Thus the post-midnight scene automatically occurs on a different day of the week! Too bad this latter fact made so many people miss the meteor shower a couple of weeks ago.