|
Big noisy bug, Mount Everest weather, ‘seeing’ electromagnetic waves
Q: Is the loud buzzing sound we hear in the summer due to the heat? Or is
it just a big bug in the trees like I always thought? — Nila
Singing males [Jim Kalisch, University of Nebraska, Entomology Department]
A: It’s a big bug in the trees. With a wingspan of up to eight inches (20
cm), it is a big insect and has the loudest insect voice. At 120 decibels, a
cicada rivals a jet engine taking off. It’s so loud that the singing male "stops
up his ears" (creases his hearing apparatus) so his own song doesn’t, literally,
deafen him.
Adult cicadas hang around in trees high on trunks or among branches and
foliage. For almost all species, the male does the singing. Some species sing in
the heat of the day, others at dusk or dawn. The terrible racket has a purpose —
to attract females. "Males in these choruses alternate bouts of singing with
short flights until they locate receptive females," says John Cooley,
entomologist at the University of Connecticut. Females can hear the males’ call
a quarter of a mile (0.4 km) away.
The cicada sings louder than grasshoppers or crickets, which rub a ridge over
a roughened edge like a fiddle bow. The cicada, on the other hand, makes a
popping noise like pressing on the top of a bulging tin can. A pair of
resonating chambers amplifies the pop, which he repeats 100 to 500 times a
second to make a buzzing roar.
His musical sound box lies at his abdomen base. It consists of drum-like
membranes held by a stiffly elastic ring, like a tambourine ring with give.
The insect doesn’t hit the membrane like a drum. Instead he pulls the
membrane down by tightening a muscle attached to it. This presses the membrane
down as we might press down on the tin can lid. He relaxes the muscle and the
membrane pops back as the lid does.
Each species sings its own unique song. Muscles attached to the ring change
the character of the sound: its shape, volume, and quality. Thus, the male
produces a signature tune, calling to only his own kind.
Further Surfing:
University of
Nebraska: Periodical cicada life stages
University of Michigan: Periodical cicada page
Rainforest-Australia.com
Mount Everest weather
Q: What is the temperature of Mount Everest? — Leeds, UK
Mount Everest [mnteverest.net, ©1999, used with permission]
A: It’s a cold place. The temperature never rises above freezing. In January,
the coldest month, it can drop to -76 degrees F (-60 C) and averages -33 (-36
C). Even in July, the warmest month, it averages -2 (-19 C).
The wind is deadly. Our highest mountain (29,029 feet [8848 m]) thrusts
itself almost into space. In the winter, the high-flying jet stream hurtles in
from the north and batters Mount Everest with hurricane-force winds exceeding
177 mph (285 km/h).
Climbers only venture onto the glacier-carved pyramid a few weeks of the
year. In May and sometimes October winds abate enough for attempts. Mountaineers
fear the unexpected. Everest drops ten feet (3 m) of snow in a blink of an eye.
Storm-force winds spring alive, carrying sand, small stones, snow, and ice aloft
to slash struggling souls.
Further Surfing:
The Weather Doctor:
The jet stream
THE WEATHER DOCTOR
WonderQuest: Lightning on Mount Everest?
AdventureWeather.com: Mount Everest weather
‘Seeing’ electromagnetic waves
Q: Your answer about light got me wondering how we "see" other
electromagnetic waves — like ultraviolet light, infrared light, and radio waves.
Why can’t we see them all? — Jack, Falls Church, Virginia
An S-band antenna that Apollo 14 astronauts used to send color live
telecasts from the Moon. [NASA]
A: All electromagnetic waves are basically the same. They carry energy
through empty space at the speed of light. We can’t see all such waves, however,
since our eyes evolved on Earth while receiving the Sun’s radiation. That’s the
kind of electromagnetic radiation we see — visible light. In the daytime, we see
blue-green light best — the peak energy from the Sun.
Our skin extends the range of electromagnetic waves that we sense beyond
visible light. We feel heat (infrared light) and sunburn (ultraviolet light).
To "see" the rest — radio waves through X-rays — we use receivers that are
sensitive to those wavelengths. The receivers translate what they "see" into
something we can sense. Some chemicals impregnated in film are sensitive to
X-rays, for example. We see the X-rays’ effects on the film after we develop it.
The rays pass through soft body parts and darken the film but are blocked by
bones and teeth.
Think of sea waves. The water undulates: peaks and valleys. The distance
between two peaks is the wavelength.
Although all electromagnetic waves are the same phenomenon, they differ
vastly in their wavelengths. Radio waves on the AM dial are about 3 football
fields long. X-rays are a hydrogen-atom long. (Related picture:
the
electromagnetic spectrum )
Our eyes can’t handle such a range of wavelengths so we supplement their
reception with radios, cameras, and the like.
Further Surfing:
HyperPhysics: The electromagnetic spectrum
Cornell University: Quicktime movie of a shockwave ‘seen’ via an X-ray camera
WonderQuest: Infrared night-vision
WonderQuest: Seeing with X-rays
HyperPhysics: Infrared ear thermometer
(Answered Nov. 21, 2003)
|