Smelling flowers and rain; Seeing the Leonid meteor shower
How do we smell a flower? Susan K. and her father, Ron, Albuquerque, New Mexico
We inhale gardenia molecules (blue) and some drift to the
smellers (yellow) lining the upper nasal cavity. Photo courtesy of
Bartleby.com, Gray's Anatomy
A: You smell the sweet scent of a gardenia because molecules escape the
flower's surface, and float into the air where your nose can detect them. A
smell travels from gardenia to nose because molecules in the air bop around,
banging into other molecules like zigzagging, tiny pool balls. Gardenia
molecules eventually reach your nose. A gardenia smells stronger when it's
warmer because warm molecules move faster. Faster molecules have more energy to
escape the surface and so more do.
Smelling is a strange sense: not like seeing or hearing. You can see a
far-away object because you receive its light waves. Likewise you hear something
from afar by receiving sound waves. Smelling--perceived in the most primitive
part of our brain--is an ancient sense, chemical in nature.
Let's return to the gardenia. You breathe in the gardenia molecules that
meandered to your nose. A paltry five percent (by volume) of your nasal cavity
receives the gardenia molecules and smells them. The smellers are postage-stamp
sized, thin patches of yellowish gray moist tissues. One on each side of the
nose, they are located behind and barely beneath the bridge of your nose. They
line the upper part of the nasal cavity directly below the brain. These are the
smell targets. Only about two to ten percent of the inhaled gardenia molecules
reach the target. There they dissolve in the wet mucus that coats the target
lining so they can reach the smell receptors.
Tiny hair-like threads--the smell receptors--cover the lining, dangle into
mucus, and reach out like antennae for matching molecules. The hairs, made of
protein and separated only by the thin goo layer from the outside world, are
extensions of your brain. And they do get damaged in that exposed location.
These unusual nerve cells last only about four to six weeks before new ones
replace them. Most nerve cells never regenerate.
Some searching hairs--which respond chemically--detect, connect, and react to
the gardenia molecules. If a receptor nerve cell reacts, it sends an ON signal.
Otherwise its message is OFF. This begins a cascade of reactions that, in a
fraction of a second, creates a perception of gardenia odor in the brain.
The olfactory circuitry can send signals corresponding to a theoretical limit
of sixteen million different smells. In 1991 neuroscientists at Harvard and
Columbia Universities discovered nearly 1,000 distinct odor receptors in humans.
Moreover, our nerve cells can recognize and respond to some 10,000 chemical
odors--an amazing repertoire.
Why does it smell so nice those first few minutes just when it starts to rain?
Susan K. and her father, Ron, Albuquerque, New Mexico
Approaching thunderstorm with lead gust front.
Rain-cooled air scuttles in front of the storm. Photo courtesy of NOAA.
A: What a delightful question! Several things cause the good smell of
rain--but the main one is humidity. Much water exists in the air just before it
rains. That moisture makes plants release aromas so there are more scents in the
air both immediately before and during rains. Also your nose functions better
when cleaned by moist air so you notice more.
This is our present knowledge. Now let's speculate on some causes. I asked
scientists around the world.
Ken Doxtader, professor of soils and crop science at Colorado State
University, says that soil contains bacteria that make aromatic gas. When you
dig in soil, you disturb the gas and free its aroma. Likewise when it rains. The
rain floods the space between soil particles, displacing the bacteria's gas, and
you smell an earthy fragrance.
Cloud water droplets form around tiny airborne clay particles. Steve Goodwin
with NASA's Lightning and Atmospheric Research thinks downdrafts associated with
rainstorms can bring those clay particles close to your nose and you may notice
an earth scent,.
The breezes and winds that swirl rain also stir up smells around you--plants,
soil, gases--so you notice them, says Robin Hicks of Melbourne, Australia's
Bureau of Meteorology.
J. Hallet at the Desert Research Institute mentions how even surface bugs
release odors when they get wet.
Why does rain stop smelling so good as it rains longer?
Susan K. and her father, Ron, Albuquerque, New Mexico
When an odor molecule reaches a nerve hair on the smell lining in the
nose, it fills a spot there. If the smell is strong (i.e., many molecules), soon
all the hairs that respond to that particular odor are filled. Those receptor
hairs have sent their smell messages to the brain and cannot send more until
they detatch their present odor chemicals. So the receptors are quiet and the
brain no longer perceives that smell. That is why you quit noticing the good
smell of rain.
Which day (18 or 19 November) will I be able to see a good meteor shower
from Mumbai, India? "About meteor shower", Mumbai, India
You can see the shower in Mumbai, India at its peak about 6 am, your time on
Nov. 19, 2007. You're lucky, because the moon sets a little after
midnight, so the skies should be dark ó at least out in the country. Of
course, Mumbai (formerly Bombay and the biggest city in India) is another story. Good luck!
Albuquerque ó half a world away ó gets to see the shower 3 am the day before,
on the 18th.
Observatory: World Time Zone Map
Observatory: U.S. Time zones
U.S. Naval Observatory:
(Answered Nov. 15, 2002; updated April 11, 2009)