scienceillustrated.com.au | 17HUMANS That grit in the corner of
the eye which many people experience
when they wake up in the morning is a
small, dried-up lump of dirt and dead
cells. During the day, the tear film of
the eye (consisting of water, oil-like
lipids and hydrophilic mucins) removes
the waste from the surface of the eye
as we blink. But at night, the dirt is no
longer carried away, collecting into a
small lump at the corner of the eye.
A few people produce grit during
the day, often due to the fact that
their tear film is less efficient. The
phenomenon can also occur if you are
in a room with very dry air, making the
tear fluid evaporate faster than the eye
glands can produce new fluid.Problems with extra grit in the eyes
are also experienced by people with
allergies, such as those connected
with hay fever. Large quantities of grit
might also be a sign of eye disease,
so if in doubt, consult your doctor.233 annual lightning bolts/km^2 - For 260 days a year, Lake
Maracaibo in Venezuela is tormented by a thunderstorm
known as “the everlasting storm”. The weather phenomenon
is probably due to the high location and air humidity.Lake Maracaibo, Venezuela
KAMPENE,
DR CONGO
177 annual
bolts/km^23 By Lake Kivu, solar
heating causes
intense air
currents which
mix with the
moisture from
the lake.CÁCERES,
COLOMBIA
172 annual
bolts/km^24 Moist winds from the wide
Cauca River and
the mountains
surrounding the
city make Cáceres
Colombia's
lightning capital.SAKE,
DR CONGO
143 annual
bolts/km^25 Intense thunder-
storms close to
the Equator place
the DR Congo
high on NASA’s
‘top 500’ list of
lightning locales.KABARE,
DR CONGO
205 annual
bolts/km^22 Kabare on the western shore
of Lake Kivu in the
DR Congo was the
world's lightning
capital until 2016,
when NASA pub-
lished a new map.TOP 5 · Where does lightning strike most frequently?
Eye grit consists of dirt and dead cells
which have not been removed.1
What makes up grit in the eyes?
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Launched in 2016, Jason-3 will be
Earth’s primary water level
satellite up until 2021.
local effects, such as in Scandinavia, where the
land mass is rising compared with the rest of the
world. The weight of ice masses during the most
recent ice age had pushed it down, but since the
glaciers melted approximately 20,000-15,
years ago and their weight disappeared, the
bedrock began to rise again. So a local water-level
marker in a harbour in the Gulf of Bothnia – such
as in Luleå in Sweden or Oulu in Finland – would
indicate that water levels there are falling by
about 1cm annually. However, satellite data
can show that this is a local effect, with no
relevance whatsoever to global water levels.
FLOATS REVEAL THE ORIGIN
OF WATER-LEVEL RISES
Three thousand ‘Argo’ floats measure
the temperature of the top 2000 metres
of the oceans. The data can reveal how much of
the ocean-level rise is caused by water being
warmer (and so taking up more space), and how
much is due to melting ice.
Editor: Morten Kjerside Poulsen