Why sleep is important and what happens when you don't get enough?
Importance of sleep
Sleep is essential for a person’s health
and wellbeing, according to the National Sleep Foundation (NSF). Yet
millions of people do not get enough sleep and many suffer from lack of
sleep. For example, surveys conducted by the NSF (1999-2004) reveal
that at least 40 million Americans suffer from over 70 different sleep
disorders and 60 percent of adults report having sleep problems a few
nights a week or more. Most of those with these problems go undiagnosed
and untreated. In addition, more than 40 percent of adults experience
daytime sleepiness severe enough to interfere with their daily
activities at least a few days each month - with 20 percent reporting
problem sleepiness a few days a week or more. Furthermore, 69 percent
of children experience one or more sleep problems a few nights or more
during a week.
What are the signs of excessive sleepiness?
According
to psychologist and sleep expert David F. Dinges, Ph.D., of the
Division of Sleep and Chronobiology and Department of Psychiatry at the
University of Pennsylvania School of Medicine, irritability, moodiness
and disinhibition are some of the first signs a person experiences from
lack of sleep. If a sleep-deprived person doesn’t sleep after the
initial signs, said Dinges, the person may then start to experience
apathy, slowed speech and flattened emotional responses, impaired
memory and an inability to be novel or multitask. As a person gets to
the point of falling asleep, he or she will fall into micro sleeps(5-10
seconds) that cause lapses in attention, nod off while doing an
activity like driving or reading and then finally experience hypnagogic
hallucinations, the beginning of REM sleep. (Dinges, Sleep, Sleepiness
and Performance, 1991)
Amount of sleep needed
Everyone’s
individual sleep needs vary. In general, most healthy adults are built
for 16 hours of wakefulness and need an average of eight hours of sleep
a night. However, some individuals are able to ******** without
sleepiness or drowsiness after as little as six hours of sleep. Others
can't perform at their peak unless they've slept ten hours. And,
contrary to common myth, the need for sleep doesn't decline with age
but the ability to sleep for six to eight hours at one time may be
reduced. (Van Dongen & Dinges, Principles & Practice of Sleep
Medicine, 2000)
What causes sleep problems?
Psychologists
and other scientists who study the causes of sleep disorders have shown
that such problems can directly or indirectly be tied to abnormalities
in the following systems: Physiological systems
Brain and nervous system Cardiovascular system Metabolic ********s Immune system Furthermore, unhealthy conditions, disorders and diseases can also cause sleep problems, including:
Pathological sleepiness, insomnia and accidents Hypertension and elevated cardiovascular risks (MI, stroke) Emotional disorders (depression, bipolar disorder) Obesity; metabolic syndrome and diabetes Alcohol and drug abuse (Dinges, 2004) Groups
that are at particular risk for sleep deprivation include night shift
workers, physicians (average sleep = 6.5 hours a day; residents = 5
hours a day), truck drivers, parents and teenagers. (American Academy
of Sleep Medicine and National Heart, Lung, and Blood Institute Working
Group on Problem Sleepiness. 1997). http://www.apa.org
A
clear cloudless day-time sky is blue because molecules in the air
scatter blue light from the sun more than they scatter red light. When
we look towards the sun at sunset, we see red and orange colours
because the blue light has been scattered out and away from the line of
sight.
The white light from the sun is a mixture of all colours
of the rainbow. This was demonstrated by Isaac Newton, who used a
prism to separate the different colours and so form a spectrum. The
colours of light are distinguished by their different wavelengths. The
visible part of the spectrum ranges from red light with a wavelength of
about 720 nm, to violet with a wavelength of about 380 nm, with orange,
yellow, green, blue and indigo between. The three different types of
colour receptors in the retina of the human eye respond most strongly
to red, green and blue wavelengths, giving us our colour vision.
Tyndall Effect
The
first steps towards correctly explaining the colour of the sky were
taken by John Tyndall in 1859. He discovered that when light passes
through a clear fluid holding small particles in suspension, the
shorter blue wavelengths are scattered more strongly than the red.
This can be demonstrated by shining a beam of white light through a
tank of water with a little milk or soap mixed in. From the side, the
beam can be seen by the blue light it scatters; but the light seen
directly from the end is reddened after it has passed through the
tank. The scattered light can also be shown to be polarised using a
filter of polarised light, just as the sky appears a deeper blue
through polaroid sun glasses.
This is most correctly called the
Tyndall effect, but it is more commonly known to physicists as Rayleigh
scattering--after Lord Rayleigh, who studied it in more detail a few
years later. He showed that the amount of light scattered is inversely
proportional to the fourth power of wavelength for sufficiently small
particles. It follows that blue light is scattered more than red light
by a factor of (700/400)4 ~= 10.
Dust or Molecules?
Tyndall
and Rayleigh thought that the blue colour of the sky must be due to
small particles of dust and droplets of water vapour in the
atmosphere. Even today, people sometimes incorrectly say that this is
the case. Later scientists realised that if this were true, there
would be more variation of sky colour with humidity or haze conditions
than was actually observed, so they supposed correctly that the
molecules of oxygen and nitrogen in the air are sufficient to account
for the scattering. The case was finally settled by Einstein in 1911,
who calculated the detailed formula for the scattering of light from
molecules; and this was found to be in agreement with experiment. He
was even able to use the calculation as a further verification of
Avogadro's number when compared with observation. The molecules are
able to scatter light because the electromagnetic field of the light
waves induces electric dipole moments in the molecules.
Why not violet?
If
shorter wavelengths are scattered most strongly, then there is a puzzle
as to why the sky does not appear violet, the colour with the shortest
visible wavelength. The spectrum of light emission from the sun is not
constant at all wavelengths, and additionally is absorbed by the high
atmosphere, so there is less violet in the light. Our eyes are also
less sensitive to violet. That's part of the answer; yet a rainbow
shows that there remains a significant amount of visible light coloured
indigo and violet beyond the blue. The rest of the answer to this
puzzle lies in the way our vision works. We have three types of colour
receptors, or cones, in our retina. They are called red, blue and
green because they respond most strongly to light at those
wavelengths. As they are stimulated in different proportions, our
visual system constructs the colours we see.
Response curves for the three types of cone in the human eye
When
we look up at the sky, the red cones respond to the small amount of
scattered red light, but also less strongly to orange and yellow
wavelengths. The green cones respond to yellow and the more
strongly-scattered green and green-blue wavelengths. The blue cones
are stimulated by colours near blue wavelengths which are very strongly
scattered. If there were no indigo and violet in the spectrum, the sky
would appear blue with a slight green tinge. However, the most
strongly scattered indigo and violet wavelengths stimulate the red
cones slightly as well as the blue, which is why these colours appear
blue with an added red tinge. The net effect is that the red and green
cones are stimulated about equally by the light from the sky, while the
blue is stimulated more strongly. This combination accounts for the
pale sky blue colour. It may not be a coincidence that our vision is
adjusted to see the sky as a pure hue. We have evolved to fit in with
our environment; and the ability to separate natural colours most
clearly is probably a survival advantage.
A multi-coloured sunset over the Firth of Forth in Scotland.
Sunsets
When
the air is clear the sunset will appear yellow, because the light from
the sun has passed a long distance through air and some of the blue
light has been scattered away. If the air is polluted with small
particles, natural or otherwise, the sunset will be more red. Sunsets
over the sea may also be orange, due to salt particles in the air,
which are effective Tyndall scatterers. The sky around the sun is seen
reddened, as well as the light coming directly from the sun. This is
because all light is scattered relatively well through small
angles--but blue light is then more likely to be scattered twice or
more over the greater distances, leaving the yellow, red and orange
colours.
A blue haze over the mountains of Les Vosges in France.
Blue Haze and Blue Moon
Clouds
and dust haze appear white because they consist of particles larger
than the wavelengths of light, which scatter all wavelengths equally
(Mie scattering). But sometimes there might be other particles in the
air that are much smaller. Some mountainous regions are famous for
their blue haze. Aerosols of terpenes from the vegetation react with
ozone in the atmosphere to form small particles about 200 nm across,
and these particles scatter the blue light. A forest fire or volcanic
eruption may occasionally fill the atmosphere with fine particles of
500-800 nm across, being the right size to scatter red light. This
gives the opposite to the usual Tyndall effect, and may cause the moon
to have a blue tinge since the red light has been scattered out. This
is a very rare phenomenon--occurring literally once in a blue moon.
Opalescence
The
Tyndall effect is responsible for some other blue coloration's in
nature: such as blue eyes, the opalescence of some gem stones, and the
colour in the blue jay's wing. The colours can vary according to the
size of the scattering particles. When a fluid is near its critical
temperature and pressure, tiny density fluctuations are responsible for
a blue coloration known as critical opalescence. People have also
copied these natural effects by making ornamental glasses impregnated
with particles, to give the glass a blue sheen. But not all blue
colouring in nature is caused by scattering. Light under the sea is
blue because water absorbs longer wavelength of light through distances
over about 20 metres. When viewed from the beach, the sea is also blue
because it reflects the sky, of course. Some birds and butterflies get
their blue colorations by diffraction effects.
Why is the Mars sky red?
Images
sent back from the Viking Mars landers in 1977 and from Pathfinder in
1997 showed a red sky seen from the Martian surface. This was due to
red iron-rich dusts thrown up in the dust storms occurring from time to
time on Mars. The colour of the Mars sky will change according to
weather conditions. It should be blue when there have been no recent
storms, but it will be darker than the earth's daytime sky because of
Mars' thinner atmosphere.
In an informal poll of 10,000
junior-high-school children, Pluto was the overwhelming favorite among
the 9 planets. The poll was simply a measure of how much noise the
children made during a tour of the solar system in a planetarium show I
presented live to groups of 500 children at a time. They consistently
cheered the loudest for Pluto, especially when I recited the planets in
sequence, aided by the time-honored mnemonic My Very Educated Mother
Just Served Us Nine Pizzas.
But Pluto has “peculiar” written all
over it. Found by Lowell Observatory astronomer Clyde W. Tombaugh in
1930, Pluto was discovered the same year that Walt Disney created the
lovable, slow-witted bloodhound that shares its name. Pluto’s orbit
is tilted 17 degrees out of the plane of the solar system, 2 1/2 times
that of Mercury. Pluto moves in the most eccentric ellipse and is the
only planet whose orbit crosses that of another planet. Pluto has
tidally locked the rotation of its moon Charon, forcing it to forever
show the same face to Plutonians. Pluto is in good company here.
Earth has tidally locked the rotation of its moon (the Moon) so that it
always shows the same face to Earthlings. The embarrassing part is
that Charon is so large compared with Pluto that its tidal forces have
tidally locked Pluto’s rotation where both moon and planet show the
same side to each other as they waltz forever in space. With a diameter
of 1,400 miles, Pluto is, by far, the smallest planet. Seven moons in
the solar system are larger: Io, Europa, Ganymede, Callisto, Titan,
Triton, and of course, Earth’s Moon (although Mercury is smaller than
both Ganymede and Titan). Finally, neither rocky, nor gaseous, Pluto
is the only planet made primarily of ices.
Maybe Pluto isn’t really a planet.
Dare
I have made such a suggestion when Clyde Tombaugh’s body is barely
cold? Tombaugh died in 1997, at the age of ninety, seemingly secure in
his status as the third person ever to discover a planet in our solar
system. But there is no question that if Pluto were discovered today,
it would not be classified as a planet.
William Herschel
discovered Uranus in 1781, and Johann Galle discovered Neptune in
1846. Few people know, however, that Giuseppe Piazzi discovered the
planet Ceres in 1801, orbiting the Sun between Mars and Jupiter. But
astronomers rapidly determined that Ceres was much, much smaller than
any other planet: at 600 miles in diameter, it was dwarfed by Mercury,
the reigning smallest planet. Maybe an object can be too small to be
defined as a planet. Shortly after 1801, other small objects were
found in orbits similar to that of Ceres. A new class of object had
been identified: the rocky asteroids
Ceres was discovered first
because it is the brightest and largest. At twice the mass of all the
other asteroids combined, of which there are thousands known and
millions that await discovery, Ceres swiftly went from being the
smallest in the class of planet to being the largest in the class of
asteroid.
How about Pluto? The more we learned about Pluto, the
more it did not fit any reasonable classification scheme that applied
to the other planets. It was in a class by itself. But can you have a
class of one? Should you have a class of one?
In 1992, David
Jewitt of the University of Hawaii and Jane Luu of Harvard began to
discover icy bodies just beyond the orbit of Neptune. Since then,
nearly a thousand such objects have been discovered with similar
properties: They are small, they are icy, they all orbit just beyond
Neptune, they have somewhat eccentric paths, and their orbits are
tipped out of the plane of the solar system. This new class of objects
was duly named the Kuiper belt, in honor of the Dutch-born American
astronomer Gerard Kuiper, who in the 1950s advanced the idea that such
a belt of comets might exist.
Alas, Pluto, which is small and
icy and orbits just beyond Neptune and has an eccentric orbit that is
tipped out of the plane of the solar system, is none other than a
Kuiper belt object—a leftover comet from the solar system’s formation.
If Pluto’s orbit were ever altered so that it journeyed as close to the
Sun as Earth, Pluto would grow a tail and look like a jumbo comet. No
other planet can make this (possibly embarrassing) claim.
