Dear Tom,
A friend in Iraq has told me that, besides a lot of heat and dust, they had a lightning
storm—no rain, no thunder—just lightning. How can you have lightning and no
thunder?
Mary Abuja, San Diego
Dear Mary,
Thunder is always a by-product of lightning, but sometimes we are too far away to
hear it.
A lightning spark can heat the air through which it passes to 54,000 degrees
practically instantaneously. Such extreme heating causes air to expand explosively,
followed immediately by cooling and rapid contraction. That physical process sets up
sound waves that blast outward, and we hear them as thunder.
However, thunder dampens quickly as it spreads and it rarely carries more than 15
miles from its source, whereas lightning bolts are often visible at distances beyond
50 miles if intervening clouds are not present.
