54 | New Scientist | 7 November 2020Double up
Why is it that when I sneeze,
I almost always do so twice?Geoff Broughton
Abingdon-on-Thames,
Oxfordshire, UK
Only twice? My wife always
releases a volley of six loud
sneezes. There is palpable
tension in the room if numbers
five and six are momentarily
delayed. How can her nasal
system reliably count to six
while under such strain?Taylor Rey
Suwanee, Georgia, US
Almost every time I sneeze, I
do so seven times in a row. The
sneezes come in fast succession,
but occasionally the last one
lags behind by a few seconds.Harsha Kariyawasam
Royal National Throat, Nose
and Ear Hospital, London, UK
Sneezing is an underappreciated
upper-airway event. It is a critical
airway protection mechanism thatprevents the entry and depositing
of potentially hazardous agents
into the nose.
It is normal to sneeze two or
three times a day. This indicates
that our nasal defences are active
and working. Frequently, one
sneeze isn’t enough, so it is
promptly followed by another
to ensure that any inhaled
threats are fully expelled.
In conditions such as hay
fever or rhinitis, there is often
irritation of the sensory nerves
of the nose such that the sneezing
reflex activation threshold is
lowered. This results in anything
from allergens to temperature
change and even strong smells
activating a sneeze.Want to send us a question or answer?
Email us at [email protected]
Questions should be about everyday science phenomena
Full terms and conditions at newscientist.com/lw-termsThe back pages Almost the last word
BEN^ HALL/NAT
UREPLThe brain doesn’t regulate or
“count” sneezes, as sneezing is
driven by a neuronal/muscular
reflex. It is an involuntary act.Rainbow riot
I have seen many double rainbows,
but can you get triple or quadruple
ones? If so, where are the best
places to see them? What is the
maximum number that could
occur at the same time?Len Winokur
Leeds, UK
We mostly only see rainbows
when the sun is behind us. The
reason is that light from the sun
is internally reflected by the back
of raindrops to re-emerge towards
us. As it enters and leaves the
drop, the white light is splitinto colours. Redder wavelengths
emerge at wider angles than
bluer ones, hence why red always
appears as the outermost band
of the primary bow and violet
as the innermost.
Not all the original light escapes
first time round, however. Some
of it undergoes a second internal
reflection before re-emerging.
This has three consequences.
Firstly, the secondary bow’s
colours now emerge at wider
angles than those of the primary
bow, so the second rainbow always
appears above the first. Secondly,
because it is formed by less light,
the secondary bow is fainter.
Thirdly, the colour sequence of the
secondary bow is flipped, with red
now being the innermost band.
Further rainbows do occur, but
they are so faint that only in thepast decade have these been
scientifically confirmed. The
caveat with the third and fourth
bows is that they would be
behind you, so seeing them
would require facing the sun,
and they would probably get
lost in the glare.
From ground level, we never
see a bow’s full circle because
the droplets projecting its lower
section are below the horizon.
But entire 360-degree rainbows
can be seen from the air.Hugh Pumphrey
University of Edinburgh, UK
The n-th rainbow is caused by light
reflecting n times from the inside
of raindrops before escaping. Until
recently, there were a variety of
claims to have observed a third
bow, but few were credible. In
the past decade, photographs of
third and fourth bows have been
taken, emerging when the
contrast in the photograph is
very strongly enhanced.Mike Follows
Sutton Coldfield,
West Midlands, UK
The use of laser light has revealed
rainbows up to the 200th order in
the laboratory, but nothing beats
seeing rainbows in the wild.Peter Bursztyn
Barrie, Ontario, Canada
Multiple rainbows are best seen
in bright sunlight when the air is
clear and free of dust. I saw nearly
complete arcs of three rainbows
in the Great Rift valley in Kenya
about half a century ago. The
conditions were perfect: a band
of rain had cleansed the air of
dust, the sun was low on the
horizon yet still very bright
and dark rain clouds formed
the rainbows’ background.
I have seen small portions of a
third rainbow in various other
places, but these never matched
the nearly complete triple arc that
I was treated to so many years ago.This week’s new questions
Satellite limits To what extent can satellites have satellites?
Could our moon have its own moon with its own moon, for
example? Is there a limit? Joe Roberts, St Austell, Cornwall, UKFrozen flight Birds fly at tens of thousands of metres high.
Ice forms on the wings of planes at this altitude, so why
don’t the birds freeze? Jane Pickett, Hitcham, Suffolk, UKWhy don’t birds freeze
when flying at extremely
high altitudes?“ I saw nearly complete
arcs of three rainbows
in the Great Rift valley
in Kenya after a band
of rain had cleansed
the air of dust”