Expert: Tom Whiting - 7/19/2009

Question
Hello Tom.

I've been wondering: do meteor/ite, asteroids that impact the earth come from totally random directions or do they tend to come from a particular area of space and so are "likely" to hit within a certain range of direction and angle?

thanks,
Dan

Answer
Hi Dan,
Sporadic meteors (and other space junk) can come in from any direction at any time (same for comets entering the inner Solar System)...in both cases, there is no preferred direction, and there is no preferred entry angle either.  We do observe more sporadic
meteors in our summer months as opposed to our N. Hemisphere winter
months, but why the one side of the orbit is more "dirty" than the
other remains a mystery.

Now meteors coming from a specific annual meteor shower are different.  As we, the Earth, intercept and pass through an old
(or current) comet's orbit, all those meteor shower members do have the same direction from which they come (called the radiant point in the sky) and a preferred entry speed, as you would guess.  But since annual meteor showers are simply "comet dust"...no known shower member has ever made it down all the way to hit the Earth and become a meteorite.
We enjoy some 60-100 meteors per hour in a dark sky on the nights
of August 11 (Perseids), October 21 (Orionids), November 17
(Leonids), and December 13 (Geminids) every year as they are annual
events.  And there are many minor showers throughout the year producing 1 to 5 meteors per hour, but astronomers don't usually
go out of their way to watch them.
Oh, for terminology, a meteor is the proper term when the body
is visible and giving off light and heat. Before atmospheric impact,
it's a meteoroid and if it strikes the Earth, a meteorite. Try to
avoid terms like shooting or falling stars, as these have nothing
to do with stars, as was originally thought a long time ago.
Clear Skies,
Tom Whiting
Erie, PA USA