With this morning’s news of an exploding fireball in Russia injuring hundreds of people, you might feel that worry is the mildest of emotions! Fireballs happen when larger space rocks burn up in the Earth’s atmosphere and for the early morning commuters in Chelyabinsk it was quite a show! Youtube has plenty of videos of the event, showing the bright fireball, smoke train and even a few booms.
This fireball has made the news, but fireballs are fairly common. The American Meteor Society has 750 reports found in the last 30 days and that is only from the US. A fireball was seen from Ireland last September.
Fireballs are very bright meteors. Generally if a meteor is brighter than the planet Venus it is considered a fireball. The brightness will depend on the viewer’s distance from the meteor – it will be brighter if it passes directly overhead, since this means it will be closer. If it is seen nearer to the horizon, it is further away, so will seem dimmer.
Today’s meteor produced bangs and booms that are reported to have broken windows. This is less common, but has been heard before. This meteor was a piece of space rock that just happened to hit the Earth’s atmosphere. For it to be this bright, it was probably a large rock – perhaps as big as a car!
This is considerably smaller than asteroid 2012 DA14. This asteroid, discovered last year, is about 50 m across. It will pass within 30 000 km of the Earth’s surface at 19:25 UT tonight. The asteroid won’t be visible from Ireland at the time of closest approach, but it will rise above the horizon shortly afterwards. A great summary of the science and the near-miss nature of this asteroid is over at the Bad Astronomy blog of Phil Plait.
A list of positions and times for your own location can be produced from heavens-above.com. This is the table for Blackrock Castle Observatory; the website also offers a sky map. I suggest that you try to “stake out” the asteroid by observing a region of the sky near a brighter star and try to catch the much fainter moving object as it goes past.
note that a negative red altitude means the asteroid is below the horizon!
a good stake out position will be between the bright stars in the handle of the Plough: