Millions of wishes remain unheard
August 14, 2015
Every year around August 12 we look up at the sky with great expectations and a list of wishes. That's when the dust track of Comet 109P/Swift-Tuttle crosses the path of planet Earth. The dust, better known as the Perseids, is actually a stream of meteors that light up the night skies when entering Earth's atmosphere.
But how many shooting stars actually burn up each night during that time? We were promised as many as 80 to 100 shooting stars per hour in reports preceding this year's event like this tweet from the Germany daily "Frankfurter Rundschau":
The perception after the highpoint did not quite meet the expectations of some social media users. This observer says she only saw planes flying overhead:
Experts admit that this year was only an average Perseid event. There was roughly one shooting star every five minutes, Rainer Kresken from the European Space Agency (ESA) said.
But what does "average" mean? And for that matter, what do "a lot" and "few" mean? Would 100 shooting stars per hour be "many"? And how does all this compare to recent years?
We asked those who count shooting stars professionally.
Detlef Koschny, head of the Near Earth Objects team at ESA, told us that 100 shooting stars an hour are indeed a lot: "In a normal night, you will see five to ten shooting stars per hour. Only at centennial events, like the Leonids shower of 1999, it is possible to count as many as 1,000 shooting stars per hour.
Jürgen Oberst from the German Aerospace Center (DLR) told DW that the DLR is organizing regular Perseid monitoring events to collect credible and reliable data.
The International Meteor Organization has also been gathering data on a regular basis since 2007. The Astronomers are using the Zenithal Hourly Rate (ZHR) - a figure that decribes how many shooting stars a person can see on a defined visual surface.
What does the data from recent years tell us?
Between 2007 and 2014, the average upper limit of shooting star detections varied between 50 and 90 per hour.
This year, the upper limit was around 80, for those who looked at exactly the right time and had a clear view of the night sky. The average on the night of August 12, the peak of the Perseid shower, lay at 60 shooting stars per hour. Compared to recent years, this was indeed a rather "average" value - so it's possible to understand the disappointment of those star-gazers who expected a firework, but got a measly one shooting star per minute.