54 | New Scientist | 19 February 2022
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Full terms and conditions at newscientist.com/lw-termsRed rainbow
My friend spotted a strange
red-only “rainbow” just after
sunrise (pictured below). There
was no rain, so what caused this?Daniel Bellhouse
Leeds, UK
Red rainbows form in the same
way as the usual multicolour
ones, from light reflecting off
the rear internal surface of water
droplets in the atmosphere.
However, during sunrise and
sunset, rays from the sun travel
a longer path through the lower
atmosphere. These rays are
scattered by air molecules and
dust. Shorter-wavelength blues
and greens are scattered the
most, so the remaining light
is richer in longer-wavelength
reds and yellows.
As the majority of the
transmitted light is now in the
red spectrum, this is the light
seen reflected back from the
water droplets, resulting in an
almost exclusively red rainbow.
This mechanism is also the
cause of beautiful red sunrises
and sunsets.Richard Swifte
Darmstadt, Germany
Rainbows with a red or pink
hue are ordinary rainbows that
happen to occur when the sun
is low in the sky and appear
redder than when it is higher up.
As for the absence of rain, it
may not have been raining at
the place where this photograph
was taken, but the picture shows
some clouds in the sky.
There was probably
a localised shower some
distance away in front of the
photographer, with enough
rain to produce the rainbow.GUY^ BEL
L/SHUTT
ER
ST
OCKYoung and loud
Babies and children make a lot
of noise when they cry and shriek.
Why do the young of other animals
seem generally much quieter?Vivienne Peters
Sydney, Australia
Young humans emit their
compelling cries to obtain
proximity to their caregivers,
who then provide food, protection
and reassurance. Babies aren’t
mobile for about nine months
after birth, so they need an
effective alternative method of
summoning help to optimise
their survival in infancy.
In human evolutionary history,
perhaps babies and young
children who were less vocal
received less care. Conversely,caregivers who didn’t feel
spurred on by the sound of their
offspring’s cry may have been
more inclined to disregard their
needs. Along with the ability
to smile and look cute, infants
who could wail and scream to
responsive and well-motivated
caregivers must have increased
their chances of survival.
If we look elsewhere in the
animal kingdom for creatures
that are equally immobile for
a period of time after birth, the
most obvious example is birds.
Baby birds in a nest can also make
a lot of noise, which prompts
their parents to attend to them.
Both humans and birds grow
up to be quite talkative as adults.
Perhaps the development of
human and bird language has
a direct relationship to the levelof helplessness seen in infancy.
Young children certainly cry less
and less as they become more
mobile and learn to use words
instead of cries.Peter Holness
Hertford, UK
Humans are apex predators.
Their babies tend to be safer than
the offspring of other animals.
Evolution has probably weeded
out youngsters of other species
that haven’t learned to “shut up
or get eaten”.David Muir
Edinburgh, UK
Babies and toddlers are
loud, demanding attention so
that they get the nurture and
nutrition needed for successful
development. As they are
generally under the protection
of their parents and aren’t
threatened by predation, human
young can afford to be noisy. The
offspring of other animals may
make a tasty snack for predators
when their parents are off looking
for food, so they have to keep quiet
to avoid unwanted attention.
When parents return with
food, young birds can certainly
be loud, as siblings compete for
parental attention and associated
sustenance. This short-term risk
is worth taking as any individual
advantage that results increases
that bird’s chances of passing on
its genes later in life.Nick and Loraine Baker
Colchester, Essex, UK
How does the questioner know
that animal babies don’t sound
just as loud to their animal
parents? (Here, we are referring
to large animals and birds, rather
than a wider range of organisms,
many of which don’t vocalise.)
A baby’s cry contains
frequencies to which the human
ear is most sensitive; a puppy’s
little whines and whimpers
probably sound annoyingly loudThis week’s new questions
Mood music I am a big fan of classical music. Why does some
music evoke certain emotions in the brain, even if it doesn’t
have any lyrics? Joseph Kostousov, Calgary, CanadaGreen eating We are told “eat your greens”, but is there any
reason why the green parts of plants are an essential part of
our diet? Tony Blake, Adelaide, South AustraliaWhat exactly is going on
to make some music tug
at the heartstrings?