Light show
Question: Why are the Northern and Southern Lights鈥攖he Earth鈥檚
auroras鈥攂oth made up of changing colours?
Answer: The auroras occur because charged particles from the Sun are carried
on the solar wind to the Earth.
These charged particles enter the Earth鈥檚 atmosphere and travel towards the
North and South Poles. While on their journey to the poles, the charged
particles interact with the different atoms that are present in our atmosphere,
making them glow.
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When atoms such as oxygen and nitrogen are hit, electrons are knocked away
and this leaves them in an excited state. The excited atoms emit radiation at
different wavelengths, creating the different colours that can be observed in
auroras.
The colours that you can see depend on the type of atom being struck by the
charged particle and at what height this collision occurs.
When the collisions between the charged particles and atoms occur near the
Earth鈥檚 surface, the molecules de-excite before they are able to radiate any
colour. However, if the collisions occur at altitude you will see a variety of
colours.
Blue colours are created by nitrogen when it becomes excited at less than 100
kilometres up in the ionosphere. Green-yellow colours occur when oxygen found
between 90 and 150 kilometres high is excited. Red colours occur when oxygen at
more than 150 kilometres or hydrogen at more than 120 kilometres high are struck
by the charged particles. If oxygen and nitrogen are both present, then an
interesting variety of blue, red and green colours can be observed.
Becky Morris (aged 13)
Deal, Kent
Answer: The minority gases in the atmosphere, such as neon, helium, hydrogen
and argon, give off visible light. However, because they are in smaller
concentrations than nitrogen and oxygen, they are rarely seen, except sometimes
as splashes of colour within an aurora.
Because auroras usually contain more than one type of gas, some displays may
have many colours at once. Near dawn or dusk an aurora may lie in direct
sunlight, making it appear purple. The display has to be reasonably bright for
the colour to be seen, otherwise the aurora appears white or colourless.
The most common colour for an aurora is green, caused by the presence of
oxygen.
Katrina McDonnell
Macquarie University, Sydney
Ancestral vinegar
Question: During the Second World War we would often find a jelly-like
substance in our vinegar bottle. My mother called it 鈥渕other-of-vinegar鈥�. Is it
true that if you put this into water it will turn into vinegar? Why don鈥檛 we see
it any more?
Answer: The jelly-like substance mother-of-vinegar is in fact a mass
of cells of the bacterium Acetobacter aceti var. xylinum.
Acetobacter species are used in the production of vinegar where they
oxidise ethanol to ethanoic (acetic) acid, the substance that gives vinegar its
characteristic sourness. Nowadays, commercial vinegar is pasteurised before
bottling, so you tend not to see mother-of-vinegar develop. In the past, this
was not the case.
The gelatinous character of the material is due to the bacterium鈥檚 ability to
produce copious quantities of cellulose. Some strains growing on the surface of
an alcoholic liquid can produce a solid gelatinous mass that can grow to several
centimetres thick. In the Philippines this property is exploited to make the
traditional product known as nata de coco or nata de pina.
These are simply cubes of bacterial cellulose sweetened and then eaten as a
dessert.
You will not produce vinegar if you add mother-of-vinegar to water, but you
will if you add it to an alcoholic liquid such as beer or wine and then leave it
exposed to the air for a while.
Martin Adams
Reader in Food Microbiology
School of Biomedical and Life Sciences
University of Surrey
This week鈥檚 questions
Glorious mud: While on holiday in North Wales recently I ventured out on the
Lavan Sands, a vast area of mud that is exposed when the tide retreats from the
Menai Straits. In no time at all, I found myself up to my knees in mud and
eventually returned to shore extremely dirty and minus my rubber Wellington
boots, sucked from my feet by the mire. Has anyone devised any footwear that
makes it possible to trek across soft mud? I would assume that the obvious
solution of round, flat 鈥渄uck鈥檚 feet鈥� shoes would fail, as suction would make
them stick to the mud鈥檚 surface, making walking nigh on impossible.
Molly Nicholas
Rickmansworth, Hertfordshire
Out of your skull: This is a question that has been haunting me for some time
and giving me many a sleepless night.
If your eyes were (very carefully) popped out of your head, turned upside
down, and placed back in their sockets would you see the world upside down?
Would the brain be capable of adjusting to this kind of change? And if so,
how?
And lastly, what would happen if you looked down at your feet?
Matthew Behrendt
Australia
Snails鈥� pace: Everyone knows that conventional letter post is referred to by
e-mail users as 鈥渟nail mail鈥�. I wonder if this dismissive term may be really
accurate.
The other day I posted a letter to my parents who live about 25 kilometres
away from me. It arrived two days later. I calcultaed that the average speed of
this letter鈥檚 journey was around 0.5 kilometres per hour.
If I had used the cheaper second-class post, the letter would typically
travel at 0.25 kilometres per hour.
How fast does a snail travel? Is snail mail now actually slower than a snail,
or does Britain鈥檚 Royal Mail still have some way to go before it is challenged
by a humble mollusc?
Jeremy Holland
London
Hot bodies: Why is the body temperature of mammals 37 掳C? It seems
extraordinarily high when you consider that it is hotter than most environments
on Earth. What purpose does this serve?
Michael Page
London