The largest fireball since the Chelyabinsk blast in February 2013 has been revealed, detected on February 6 at 2 p.m. UTC in the South Atlantic Ocean. But this event happened in the middle of the ocean, about 1,850 kilometers (1,150 miles) south-east of Rio de Janeiro in Brazil, so it likely wasn't seen directly or caught on camera.
Data released by NASA shows that the meteor released an energy equivalent to 12,000 tonnes (13,000 tons) of TNT, and it was moving at over 15.5 kilometers per second (9.6 miles per second). It disintegrated at a height of about 31 kilometers (19 miles) and it had a diameter of about 7 meters (23 feet), calculated based on its kinetic energy.
While 12,000 tonnes of TNT seems like a very large number, it pales in comparison to the Chelyabinsk impact, which was 40 times more energetic and released 450,000 tonnes (500,000 tons) of TNT. The Chelyabinsk event, although not incredibly dangerous in itself, injured over 1,000 people due to windows breaking. If this event had happened over a populated area, it would have at most rattled some windows and scared a few people, according to Phil Plait at Slate.
Relative location of the fireball. Google Maps
The report and information on the event were given to NASA by the U.S. government. Detecting atmospheric explosions is most likely a high priority of several branches of the U.S. military, so a fireball of such magnitude could have been easily picked up. Satellite imagery and infrasound atmospheric microphones could both be used to detect an impact like this.
These events, although unusual, are not as uncommon as one might think. Meteoroids of about 10 meters (33 feet) in diameter hit Earth about once every 10 years, although some argue that it might be closer to a yearly occurrence, and we get hit with much smaller debris every day. NASA has a list of some of the brightest fireballs, the NASA's Fireball and Bolide page, but it's certainly not an exhaustive list as detection is not easy.
Meteors are made up of fragments of asteroids and comets that impact our planet atmosphere. They burn quickly on their way to the ground and most of them are disintegrated high in the atmosphere. If fragments manage to reach the ground, they are called meteorites.