by Megan Argo

Stand outside under a clear night sky at any time of year for more than a few minutes, and you will eventually see a shooting star somewhere in the sky.  Pick certain times of year and you may see over one hundred in an hour.  These celestial fireworks are caused by tiny particles of rock as they fall into the Earth's atmosphere at high speed.  Our Solar System contains many billions of such particles, but they are so small and difficult to detect that we (usually) only know they are there when they interact with our atmosphere.  Many of these particles are leftover from the early solar system, or left behind when asteroids collide, but the dense streams of particles which give us the famous yearly meteor showers are left behind in the orbital paths of comets and asteroids.  Understanding the distribution of these particles is vital for keeping our satellites safe, ensuring the continued operation of the GPS and broadcast services on which our civilisation is now so reliant, and ensuring the safety of astronauts in orbit.

Looking Down on a Shooting Star" by ISS Expedition 28 crew - NASA Earth Observatory. Licensed under Public Domain via Wikimedia Commons


Fireballs are exceptionally bright events which happen when a larger meteoroid passes through the atmosphere.  Recently there have been some excellent fireballs with many thousands of witnesses, the most well-known being the bolide which exploded over Chelyabinsk, Russia, on February 15th 2013.  That event was also captured on many dashboard cameras, providing a lot of information to researchers looking for any debris left behind, allowing them to calculate an accurate trajectory.  Not all fireballs result in a ground-fall, but any material which does reach the surface of the Earth can be analysed chemically, and the results of these investigations tell us something about the parent body (a comet or asteroid) and even something about the history and formation of our Solar System.

More recently, the night of Sunday March 15th 2015 saw a massive fireball over southern Germany, Austria, Switzerland, and eastern France.  Witnesses from the region have reported the event to the International Meteor Organization (IMO), and more than 280 eyewitness reports have been collected so far.  Robin from Tuttlingen said: "The fireball was so bright that it illuminated the sky and landscape around me to twilight brightness levels."  It was also witnessed by the captain of Alitalia flight AZ153 from Brussels to Milano Linate, who spotted it from the cockpit over Alsace, France

A heat map showing the locations where people reported seeing the March 15th fireball. Courtesy of the International Meteor Organisation.


Twenty witnesses near Zurich reported a rumbling boom sound shortly after the fireball appeared.  These types of sonic effects indicate the fireball penetrated deep into the Earth's atmosphere.  An estimated trajectory, computed from the eyewitness reports, shows the fireball was travelling from north to south, starting about 25 km south of Stuttgart and ending approximately 20 km east of Zurich.  Like the Chelyabinsk event, the March 15th event was also captured by several dashboard cameras and other automated video systems.  One camera, operated by Thomas Tuchan, nicely caught the path of the fireball across the sky.

Meteors are caused by small pieces of rock, generally less than a millimetre in size.  They range in brightness from too faint to be seen with the naked eye, right up to brighter than the full moon.  The majority of meteors are at the faint end of this scale, while fireball events like these are at the extreme upper end of this range.  Almost all small meteoroids disintegrate during their passage through the atmosphere.  But sometimes, very bright fireball events can result in a meteorite fall, where the meteoroid (or parts of it, in the case of an explosion) reaches the ground.  If this happens, reports from people who saw the event are vital in determining the likely location of the debris.

Whether a fall occurs or not, the details of fireball events like this can only be determined from combining the information from many eyewitness reports.  If you see a fireball, you can help researchers by reporting what you saw in as much detail as possible.  The best way to do this is though the IMO's fireball report form.  The form is simple and guides you easily through the process of reporting your sighting, assuming no specialist knowledge of astronomy, and is available in more than 25 languages.

So, what is the best method of watching for meteors and fireballs?  Find a nice dark site, string up a hammock, and relax!

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Megan Argo is a radio astronomer who spends her working days using networks of radio telescopes to watch what happens when galaxies collide.  She is also interested in meteors and is currently the press officer for the IMO.  In her spare time she likes to go hiking and camping in wild places, and can often be found lying in a hammock under a dark sky.
Megan Argo is a radio astronomer who has worked at four institutes across three countries and two continents. She regularly observes with networks of radio telescopes spread across (at least) fifteen countries and three continents, and has conducted outreach activities from inner city Manchester to rural India and the remote outback of Western Australia.  She loves a challenge. - See more at: http://www.astronomerswithoutborders.org/321-awb-blog/dark/gam-2014-blog/2155-communication-challenges.html#sthash.HtH9cRJD.dpuf
Megan Argo is a radio astronomer who has worked at four institutes across three countries and two continents. She regularly observes with networks of radio telescopes spread across (at least) fifteen countries and three continents, and has conducted outreach activities from inner city Manchester to rural India and the remote outback of Western Australia.  She loves a challenge. - See more at: http://www.astronomerswithoutborders.org/321-awb-blog/dark/gam-2014-blog/2155-communication-challenges.html#sthash.HtH9cRJD.dpuf