The American Meteor Society has so far received over 100 reports so far of a bright fireball over California and Nevada. What is unusual about this event is that it occurred near 8:00am PDT Sunday morning April 22th, in full daylight! Being seen during daylight, most of the reports are of a white object with blue and green being most mentioned secondary colors.Â The average brightness reported by witnesses was between that of the sun and the light produced by a full moon. This event occurred near the maximum of the Lyrid meteor shower, but was most likely not associated with this shower.
There were also many reports of a sonic boom associated with this event. This indicates a portion of the meteoroid survived to low levels of the atmosphere (>5 miles altitude). Two days after this event meteorites have been found in the towns of Lotus and Coloma, California.
A fireball is a meteor that is larger than normal. Most meteors are only the size of tiny pebbles. A meteor the size of a softball can produce light equivalent to the full moon for a short instant. The reason for this is the extreme velocity at which these objects strike the atmosphere. Even the slowest meteors are still traveling at 10 miles per SECOND, which is much faster than a speeding bullet. Fireballs occur every day over all parts of the Earth. It is rare though for an individual to see more than one or two per lifetime as they can also occur during the day (when the blinding sun can obscure them), or on a cloudy night, or over the ocean where there is no one to witness them. Observing during one of the major annual meteor showers can increase your chance of seeing another bright meteor.
Fireballs often appear much closer than they really are. The AMS receives countless reports that an object landed just over the hill when in fact it was several hundred miles away and was witnessed over several states or provinces. It is your perspective that makes meteors appear to strike the horizon when in fact they are still high in the atmosphere. This is much like a jetliner seen low in your sky. It appears low to you and close to the ground, but for someone located many miles away in that direction, the jetliner is passing high overhead. Meteors become visible at approximately 50 miles above the Earth’s surface. Friction slows these objects down until they fall below the velocity necessary to produce light. At this point they still lie at least 5 miles high in the sky. They are invisible below this altitude and cannot be seen as they basically free falling to the ground at 200mph. Very few meteors actually reach the ground as 99.99% completely disintegrate while still 10-20 miles up in the atmosphere.
In the AMS fireball table, refer to event #588 for 2012.