The hot plasma within the sunspot can't move as freely as the plasma
elsewhere on the sun's surface, because it is kept pinned in place by
the magnetic field. It cools off, making that part of the sun look
Like the magnetic fields that cause them, sunspots have north and
south poles. Once created, they last for days or weeks as they move
gradually from the polar regions towards the solar equator. Sunspots
appear with varying frequency, their numbers waxing and waning on an
eleven year cycle.
What clock keeps time for the whole planet?
The source clock for the planet is the US Naval Observatory's Master
Clock. It's a network of dozens of extremely accurate clocks located
all over the planet!
These clocks communicate by electronic messages every 100 seconds.
Together, they make a very stable time standard. Their time signal is
used for many purposes, including the satellite-based Global
Positioning System and many kinds of electronic navigation systems.
Do you have a self-setting clock? Self-setting clocks receive a radio
signal that originally comes from the USNO Master Clock, and reset
themselves as needed!
What kind of creature creates underground farms?
Leaf cutter ants of Central and South America create underground
gardens of fungus for their food!
The workers cut circular pieces of leaves, then carry them into
underground chambers. They chew them up, mix them with fungus spores,
and deposit the mixture in the garden chambers.
The ants can't eat the leaves because they can't digest the cellulose
they contain. The fungus converts the cellulose into sugars, and
grows filaments (called hyphae) with swollen ends which are harvested
for food by the ants. In return, the ants protect the fungus from
competing species of fungus.
What's the best vacuum ever achieved artificially?
The best artificial vacuum is created behind the Wake Shield, a four
meter (13 feet) disk, dragged several miles behind the Space Shuttle
as it orbits the Earth. The experiment is designed to produce a super
vacuum to test new manufacturing processes.
Behind the Wake Shield, the average distance between atoms is one
millimeter (the width of a rice grain). That's ten times larger than
the best vacuum we can make on Earth!
That's still much denser than interstellar space, where atoms are
about a centimeter (under half an inch) apart, or intergalactic space,
where they can be ten meters (thirty three feet) apart.
What's the fastest sea bird?
Frigate birds are not only the fastest, but also the most acrobatic
ocean-going birds. Able to fly as fast as 93 miles per hour, they can
steal food from other birds while in flight, and snatch flying fish
right out of the air!
Specialized for flight, they are unable to land on the water and
awkward on land. They build crude nests under low bushes, and lay
only one egg at a time.
The male frigate bird has a bright red pouch on the underside of
neck, which he can inflate to attract females. When inflated, the
pouch can be seen for great distances.
Who was the first person to identify radio signals from outer space?
In 1931, a scientist named Karl Jansky was trying to find the sources
of radio static. He discovered that, while some of it came from
thunderstorms, there was also a steady hiss that repeated every day at
the same time.
Using star charts, Jansky realized that the signal was coming from
center of the Milky Way Galaxy! Since then, scientists have
discovered that there are millions of close-packed stars there, and
probably a huge black hole.
Jansky's discovery was the first radio signal known to come from
space, and it was the beginning of the field of radio astronomy.
Does the Earth ever stop vibrating?
Even when there are no earthquakes, the planet still vibrates all the
time! The tiny vibrations have recently been detected, by
high-sensitivity gravimeters (devices that sense gravitational
The Earth rings like a bell. There are several vibration patterns
repeating with cycle times of hundreds of seconds. Researchers
suspect the vibrations are caused by turbulence in the atmosphere,
but no one knows for sure.
Of course, when there is an earthquake, the entire planet vibrates
a much larger scale, as the waves spread right through the center and
out to the other side.
Where are the oldest known human footprints?
The oldest known footprints of a true, modern human were made 117,000
years ago near what is now Capetown, South Africa. They were
discovered in 1995, on a sandstone ledge at Langebaan Lagoon.
The three footprints were probably made by a woman or a young boy
walking in wet sand near the seashore. Soon after, dry sand blew
across them, and much later, the beach was buried under layers of
sediment and the prints turned to sandstone.
Scientists are excited by the find, because there are very few traces
of humans from that time period. The footprints support current
theories that humans evolved first in Africa, then spread out to the
rest of the world.
What complex creatures were the very first to evolve?
The first non-microscopic animals appeared in the Cambrian Period, 570
-505 million years ago. During that time, some amazingly strange
creatures lived in the oceans!
Cambrian ecology was very different from today's. There was no life
on land. Underwater, shrimp-like creatures crawled on the mud, eating
algae or each other. There were also sponges, mollusks, and
jellyfish, plus mysterious creatures that do not seem to fit any known
There were no fish, but there were simple swimming creatures, called
chordates, with straight, reinforced nerve tubes. These primitive
creatures were our ancestors!
What kind of worm lures its prey with a light?
The New Zealand glow worm, Arachnocampa luminosa, captures flying
insects that are attracted to its glowing body! The hungrier the worm
gets, the brighter it glows.
The glowworm is the larva of a fungus gnat, a kind of small fly.
worms are found on the dark undersides of rocky outcrops, often over
They dangle long, sticky threads that contain a paralyzing poison.
They catch and eat many kinds of small flying insects, including
adults of their own species.
The most famous place to see them is Waitomo Cave, where thousands
glowworms make the cave ceiling look like the night sky.
What's the saltiest body of water on Earth?
The saltiest natural body of water on Earth is the Dead Sea, on the
border of Jordan and Israel. It's so salty that the only life forms
that can live in it are bacteria and primitive cells called archaea.
The Dead Sea came into being millions of years ago, when a rift opened
between Syria and Africa, exposing layers of ancient, mineral-rich
stone. The salts in the Dead Sea are quite complex, including high
levels of calcium, potassium, and magnesium.
The shore of the Dead Sea is the lowest point on the surface on Earth,
about 400 meters below sea level.
How did people do math before there were calculators?
For more than three centuries before hand-held calculators became
common, the slide rule was an important tool for higher math. By
aligning two scales and moving a sliding hairline, one could do
multiplication, division, and many other functions.
The slide rule was invented in 1654, using the idea of logarithms,
developed by John Napier. The sliding scales are ruled in logarithmic
series, making it possible to do many operations by simply adding and
subtracting the distances along the scales.
The best slide rules can do calculations to three decimal places
accuracy, if you have sharp eyes and a steady hand.
Is the North Pole always in the same place?
The geographic North Pole moves by as much as 6 meters (18 feet) in a
cycle with a repeat time of about 435 days! This movement is called
the Chandler Wobble. The movement is caused by interactions between
atmospheric wind patterns and the rotating Earth, and by tidal
interactions with the Moon and Sun.
The magnetic North Pole also moves, at a much faster rate, currently
about 10 kilometers per year. Its movement is caused by changes in
the circulation of liquid iron deep within the core of the planet.
Over millions of years, the geographic poles have moved by many
thousands of miles. These much slower but much larger changes were
caused by shifts in the balance of the land and ice masses, as the
continents slowly moved around.
What kind of insect uses mothballs to protect its nest?
Naphthalene is the active ingredient in mothballs, which humans use to
kill many kinds of insects. However, there is an insect, the Formosan
subterranean termite, Coptotermes formosanus, which uses it to repel
invaders in its own nest!
The termites insulate their nests with "carton", which is a cement
made of chewed up wood. This substance is imbued with naphthalene.
Current research cannot yet explain how the naphthalene is produced or
why it is not harmful the termites.
Although traces of naphthalene occur in magnolia flowers and
secretions of white tailed deer, no other insects are known to use it
When did the first human-powered aircraft fly?
The first significant flight by a fully human-powered aircraft
happened on August 23, 1977. The craft was the Gossamer Condor,
designed and built by Paul MacCready and flown by Bryan Allen. It was
made out of cardboard, balsa wood, Mylar plastic, and piano wire!
The Gossamer Condor was powered by a single pedal-driven propeller,
and steered by flexing the wing tips. It had a 96-foot wing span, and
it weighed only 70 pounds.
The flight won the coveted Kremer Prize for the first human-powered
aircraft, by completing a 1-mile long figure-8 course. Today the
Gossamer Condor hangs in the Smithsonian, next to the Wright brothers'
What's the coldest star known?
The coldest known star is an unnamed star in a binary system (two
stars orbiting each other) about 160 light years from Earth. Its
surface temperature is only 1700 Kelvin (2600 F) which is 4100
Kelvin (7400 F) cooler than the sun!
Why is this star so cool? The other star in the binary is a smaller,
but much heavier star called a white dwarf. It orbits so close (only
about as far away as the Earth is from the moon!) that the much
heavier white dwarf has been stealing away its companion's mass.
The cool star is now only about 1/25 the mass of the sun, and still
shrinking! It's now far too small to support nuclear fusion, so it
has cooled down to a dull red glow.
When was the first paper invented?
The first true paper was made around 100 AD in China, or possibly
slightly earlier, using hemp and mulberry fibers. Later, other fibers
were used, such as tree bark and bamboo. Paper has been made from
many kinds of fibers, including even seaweed!
Although rolls of papyrus were created about 5,000 years ago in
ancient Egypt, and the word paper actually derives from the Greek and
Latin words for papyrus, technically papyrus is not paper. The same
is true for rice "paper." Both kinds of "paper" are plant materials
that have been cut or flattened.
Real paper is made by macerating (separating by soaking) the original
plant fibers and recombining them into the flat sheets, then pressing
and drying the sheets. A gluey substance is used as sizing, to hold
the fibers together and give the paper strength.
What life form has survived as spores for 30 million years?
Some bacteria trapped in amber 30 million years ago are still able to
grow into colonies! The long-lived spores were retrieved from the
abdomens of bees preserved in ancient amber, then grown on plates made
from the gelatinous material agar.
Over time, DNA in living creatures undergoes gradual changes because
of mutations. The DNA of the bacteria, which is different from
today's similar species, shows that they are genuinely ancient.
Which is the Largest Tortoise?
The Aldabra tortoise is the largest of all the tortoises. The male
Aldabra has an average shell length of about 48 inches (1.2 meters)
and an average weight of about 265 pounds (120 kilograms). Some
sources claim that males can reach 500 pounds (around 230 kilograms)
in weight. Female Aldabras tend to be significantly smaller than
Aldabra tortoises are from the Aldabra Islands in the Indian Ocean
near the Seychelles. They live in grasslands, scrub areas, and
mangrove swamps. The Aldabra tortoise feeds on grasses, sedges,
herbs, and the leaves of trees, which it fells with its enormously
Which planet is less dense than water?
Saturn is the only planet in the solar system that is less dense than
water. This means that any object with the same density as
the planet Saturn will actually float on water!
Saturn is the second largest planet in the solar system. It is
composed mainly of hydrogen gas, with a core that is probably made of
liquid hydrogen, and a small rocky body in the center.
The planet rotates so fast (once every 10 hours, 39 minutes) that
is visibly flattened at the poles due to centrifugal force. It has
eighteen known moons, more than any other planet, and it is circled by
a spectacular system of rings and ringlets made of icy particles.
Who was the first person to predict a solar eclipse?
The first person to predict an eclipse of the sun was reputedly Thales
of Miletus, a Greek philosopher, statesman, and scientist. According
to the Greek writer Xenophanes, he predicted an eclipse that took
place in 585 BC!
Thales read Babylonian astronomical records and noticed patterns
eclipse dates which allowed him to predict the date of the next
eclipse. Most scholars believe that his prediction was accurate to
within one year of the actual eclipse date.
Thales also studied mathematics, and was the first person to prove
that opposite angles of intersecting lines are equal, along with
several other important theorems. He was one of the Greek "Seven Wise
Men" whose sayings were recorded in the temple at Delphi.
Which rocket engines are the most powerful?
The three main engines of the Space Shuttle weigh less than 7,000
pounds each, but each one puts out almost a half-million pounds of
thrust. These are currently the most powerful rocket engines: each
is as powerful as seven Hoover Dams!
The Shuttle's main engines are designed to be used continuously,
and over, for as long as seven hours. Older rockets had to be
replaced after being fired just once.
Each shuttle main engine is controlled by an electronics package
containing two computers, dozens of sensors, and hundreds of other
components. Thrust, fuel mix, and steering are delicately adjusted
What was the largest predator that ever lived?
The largest predator was the megatooth shark, Carcharodon megalodon.
Their maximum length is widely debated, but most estimates are around
Megalodon evolved during the early Miocene epoch, about twenty million
years ago, and lived until about two or three million years ago.
Scientists suspect that the megatooth's main prey were the large
whales, which evolved at about the same time.
Today, the closest relative of the megatooth is the relatively puny
great white shark, which seldom gets as big as twenty feet.
What kind of man-made stuff is floating in the ocean?
Millions of objects have been lost at sea over the years! Single
accidents have released 500,000 cans of beer, 29,000 yellow ducks (and
other bathtub friends), 80,000 Nike sneakers, 5 million Lego toy
pieces, and hundreds of thousands of rubber sandals.
In addition, at any one time there are millions of chunks of trash
other objects, and fifty or more abandoned vessels, all floating free,
carried by the currents on the open ocean.
Each year, thousands of these items wash ashore on beaches around
world. Some people study their patterns of distribution, which can
reveal much about currents and ocean circulation. When an accident
releases a vast number of items, special alerts go out to beachcombers,
who watch for them and report the time and place where each object is
What clouds are the tallest, from base to top?
The tallest individual clouds are thunderstorm or cumulonimbus
clouds, which can be 60,000 feet tall, twice the height of Mt.
A thunderstorm forms when warm, moist air rises and expands. As the
air cools, some of the water vapor condenses into cloud droplets,
releasing more heat. The added heat causes the moist air to rise
In a mature thunderstorm, the updrafts can be as fast as 100 feet
second. A single thunderstorm can lift over 500,000 tons of water
into the sky, most of which falls as rain before the storm dissipates.
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