SPIDERS (ARACHNAE)
House Spider
Garden Spider
Spiders are not insects. They have eight legs rather than six, have only two sections to their bodies and have eight single eyes instead of two compound ones. There are over 3,000 species of spiders in North America, and only two are considered dangerous, the black widow (Latrodectus) and the brown recluse (Loxosceles reclusa). In comparison with many other countries, a small child can be allowed to wander barefoot without worrying that they will be bitten or even killed.
The common house spider (Tegenaria atrica) is completely harmless, though it can be quite large in country settings and moves worryingly quickly across the floor when it senses danger.
Another common sight in wooden sheds everywhere is the garden spider (Arachneus diadematus). Again, these can grow quite large with a good supply of flies and smaller spiders. It makes funnel-style webs and can be tempted out by touching a leaf or pencil to the edge of one.
There are many other species of spider and many thousands more insects with different and interesting lives and habits. The more you learn about insects, the more you understand what an incredibly complex world this actually is.
Juggling
THIS IS THE SKILL of tossing objects in the air and catching them. First of all you will need three round balls, about the size of tennis balls. You can make excellent ones by putting a couple of handfuls of rice or flour into a balloon. If you use fruit, it will be very messy, so be prepared to eat them bruised. Alternatively, juggling balls can be bought from any toy store. It looks difficult, but on average it takes about an hour to learn, two at most.
1.Hold one ball in your right hand and gently lob it into your left. Now lob it back in the direction it came. Go back and forth with this until you are comfortable.
2.Now let’s add another ball! Hold one ball in your right hand and one in your left. As you lob the ball from your right hand to your left, release the ball in your left hand and catch the incoming ball. The hard part is releasing the left-hand ball so that you lob it back to your right hand and catch it. This will take some practice, or you might pick it up immediately. Make sure both balls are flowing in a nice arc from hand to hand. This will give you more time to release and catch.
3.Ball three! Hold two balls in your right hand. Hold the third ball in your left hand. Lob the first ball from right to left and as you catch it in your left hand, release the second ball lobbing it back to your right. (This is just step 2, holding a third ball.)
The hard bit is releasing that third ball as you catch the second ball in your right hand, and lobbing the third ball back to your left hand. You must keep this lob-release-catch going from hand to hand. Practice, practice, practice!
Now for a fancy trick. Start in the beginning position (two balls in the right hand, one in the left), put your right hand behind your back and throw the two balls forward over your shoulder. As they sail over to the front, lob the left hand ball up as normal and catch the two coming over in your left and right hand. Yes, this is as hard as it sounds. Quickly lob the right-hand one to your left and catch the one in the air coming down. You are into the routine. This is an impressive start to juggling three balls, but it is very hard, so the best of luck.
Questions About the World—Part Two
1. How do we measure the earth’s circumference?
2. Why does a day have twenty-four hours?
3. How far away are the stars?
4. Why is the sky blue?
5. Why can’t we see the other side of the moon?
6. What causes the tides?
1. HOW DO WE MEASURE THE EARTH’S CIRCUMFERENCE?
The simple answer is that we use Polaris, the Pole Star. Imagine someone standing at the Equator. From their point of view the Pole Star would be on the horizon—as in the diagram. If the same person stood at the North Pole, Polaris would be almost directly overhead. It should be clear, then, that in moving north, Polaris appears to rise in the sky. A sextant can confirm the changing angle.
The angle through which the Pole Star rises is equal to the change in the observer’s latitude. If Polaris rises by ten degrees, you have traveled ten degrees of latitude.
All the observer has to do is measure how far he has traveled when Polaris has risen by one degree. Multiply that distance by 360 and you have your circumference of the earth. Easy.
The actual circumference is 24,901 miles (40,074 km) around the Equator and 24,859 miles (40,006 km) around the poles—or in rough terms 25,000 miles around, with a slightly fatter Equator. As you can see, this is not a perfect globe. The correct term is “geoid,” which just means “shaped like the earth.” When you’re a planet, you get your own word.
2. WHY DOES A DAY HAVE TWENTY-FOUR HOURS?
Well, because we say it does. The modern world uses the Roman system of measuring time from midnight to midnight—as opposed to the Greek system of measuring from sunset to sunset. The Romans also divided daylight into twelve hours. This caused difficulties, as summer hours would be longer than winter hours. When the system was made more accurate, it was sensible enough to double the twelve for the night hours. Most of the way we measure time is based on the number twelve, fractions and multiples of it, in fact—which is why we have sixty minutes and sixty seconds. The architects of the French Revolution were eager not only to introduce a decimal number system and meters to the world, but also a ten-day week, a hundred-minute hour, and a hundred-second minute. Needless to say, no one else was quite as eager.
3. HOW FAR AWAY ARE THE STARS?
Light travels at 186,000 miles (300,000 km) a second. In a year it would travel almost 6 million, million miles.
A light-year is 6 trillion miles. That is a long way by anyone’s standards.
The closest star to us is Proxima Centauri—about four and a third light-years away. That is even further. To put it another way, the light from Proxima Centauri has taken four and a third years to get here. The actual star could have blown up yesterday, but we wouldn’t know for almost five years.
The furthest stars we can see are more than a thousand light years away.
4. WHY IS THE SKY BLUE?
To understand this, it’s important to understand that color doesn’t exist as some separate thing in the world. What we call blue paint just means paint that reflects light in certain wavelengths we have learned to call “blue.” Color-blind people have eyes that work perfectly well but are different from most other eyes in just this area—how they register light wavelengths. Take a moment and think about this. Color does not exist—only reflected light exists. In a red light, blue paint will look black, as there is no blue light to reflect. In a blue light, red paint will look black.
Now, the sky is blue because blue light comes in on a short wavelength and wallops into oxygen atoms of roughly the same size. When we look up and see a blue sky, we are seeing that interaction.
At sunset, we see more red because the sunlight is passing through many more miles of atmosphere at that low angle near the horizon. The blue light interacts with the oxygen and is scattered as before—but cannot reach the eye through the extra miles this time. Instead, we see the other end of the spectrum, the red light.
5. WHY CAN’T WE SEE THE OTHER SIDE OF THE MOON?
Until the late twentieth century, mankind had no idea what lurked on the dark side of the moon. This is because the same face was presented to observers on earth all the way through the lunar cycle.
The moon takes twenty-nine and a half days to go around the earth. It does actually rotate on its own axis, completing a full turn in . . . twenty-nine and a half days. As these two are the same, it always shows the same face.
The best way to demonstrate this is with a tennis ball and a basketball. Mark the side of the tennis ball and place the basketball somewhere where it can’t roll away—or have someone hold it. Now move the tennis ball around your earth, keeping the same side always inward. By the time you have gone all the way arou
nd, the tennis ball will also have turned on its own axis.
6. WHAT CAUSES THE TIDES?
Following neatly on from the last question, the answer is gravity—from the moon and the sun. The moon’s massive presence overhead actually pulls oceans out of place. These two diagrams are deliberately exaggerated to show the effect. They are not to scale!
Spring Tide—New Moon
Spring Tide—Full Moon
The seas move more easily than land, though the whole planet is actually affected. What happens in practice is that the earth’s own spin produces two high and two low tides each day. It takes twelve hours to expose the other side of the earth to the moon’s gravity, a little like squeezing a balloon twice around the middle in twenty-four hours. Both ends bulge to create high tides and then withdraw to create low tides.
The diagram above is actually of a “spring” tide, which occurs twice a month at the new and full moon. The name has nothing to do with the season. When the moon is in line with the sun and the earth, the tide is particularly strong. The weakest tides are known as “neap” tides, and occur at the quarter moon, as in this diagram. The moon’s effect is lessened by being out of line with the sun.
Neap Tide—Quarter Moon
Astronomy—the Study of the Heavens
ASTRONOMY IS NOT ASTROLOGY. Astrology is nonsense. The idea that our lives can be affected by the flight of planets is not even slightly plausible. Venus may have been named after a goddess of love, but its movement can have no bearing on our own chances for romance. The planet could equally have been called by another name, after all. The first (and last) point about star watching is that it is science and not superstition—but the stories of ancient heroes like Orion can be fascinating. Knowing Orion chases Taurus works as a mnemonic—an aid to memory.
There are eighty-eight constellations that can be seen in the night sky at different times of the year and all the visible stars have names, or at least numbers. As the earth rotates, so their positions change and you can follow them through the seasons (see Star Maps).
This chapter is an introduction to sky watching. Most of us live and work in noisy, artificial environments. Light pollution from cities hides the glories of the night sky, but those who are curious always find ways to explore beyond them. Naked-eye astronomy is easy and fun and can be done alone or with friends. This chapter will make you more familiar with the wonders of the universe.
Look at the stars! look, look up at the skies!
O look at all the fire-folk sitting in the air!
The bright boroughs, the circle-citadels there!
Gerard Manley Hopkins
Since the dawn of time, mankind has grouped stars into constellations, filling the heavens with heroes, gods and fantastic creatures. The myths and histories of lost civilizations can be found above us and help us understand the legends and stories that chart our own time.
One of the most easily recognizable constellations, and a great way to start finding your way around the skies, is Ursa Major, the Great Bear.
This constellation gets its name from the Greek legend of Callisto, a nymph transformed by Zeus into a she-bear. Many Native American tribes have also seen this constellation as a bear. Maybe the ancient Greeks sailed further than we realize! Particularly famous is the group of seven stars often called the Big Dipper or the Plow. In Cherokee legend, the handle of the Big Dipper is seen as a team of hunters chasing the bear, who is visible high in the sky in spring until he sets on autumn evenings. Each day they chase the bear further west. Boys, you will need your compass.
This distinctive star system has been noted by Shakespeare and Tennyson. In Hindu mythology, the Big Dipper is seen as the home of the seven great sages. The Chinese saw them as the masters of heavenly reality; the Egyptians, as the thigh of a bull. The Europeans saw a wagon and the Anglo-Saxons associated it with the legends surrounding King Arthur.
In ancient times, north could be plotted using the star Alkaid, in the Big Dipper. Today north can be found in Ursa Minor, a constellation that lies almost alongside Ursa Major. In Greek legend this constellation was named after Arcas, the son of Callisto. He too was changed into a bear and left to follow his mother eternally around the north celestial pole.
Finding north, and with it all other points on the compass, is as important as knowing your address. It is one of the first steps to understanding where you are. The key star is called Polaris (see below), the Pole Star for the northern hemisphere.
From the Big Dipper, mentally draw a line through the stars Dubhe and Merak, extend upward five times its length and you hit Polaris. Face Polaris and you are facing north. If there is light pollution, it may be the only star visible in Ursa Minor.
If you are in the southern hemisphere, then finding south is just as important, and almost as easy. First identify the Southern Cross (see below) and mentally extend a line down from the long arm. To the left are two stars, Rigil Kentaurus and Hadar, known as the pointers. Extend a line down from between them until it crosses the first line. This point is directly above south.
On a clear night in winter in the northern hemisphere if you face south, away from the Pole Star, the constellation of Orion is the chief attraction. It is characterized by its three belt stars with the red star Betelgeuse above and Rigel below.
In Greek mythology, Orion was a great hunter. Artemis, the goddess of the moon and the hunt, fell in love with him and neglected her duties of lighting the night sky. As punishment, her brother, Apollo, tricked her into slaying him from afar with an arrow. When she realized what she had done, she put his body in the sky with his two war dogs, Canis Major and Canis Minor. According to ancient Greek astronomers, her grief explains the sad, cold look of the moon.
The brightest star in the sky is in Canis Major—Sirius, the Dog Star. Sirius rises in the east in late summer, at the heels of Orion, hunting with him through the winter.
Above and to the right of Orion and his dogs is their prey, Taurus, the bull. Its red eye looks back nervously—the star Aldebaran. Since the time of the ancient Babylonians, some 5000 years ago, this constellation has been seen as a bull. Bulls have been worshipped since ancient times as symbols of strength and fertility. The Greeks saw the constellation as Zeus disguised as a bull. In this form he seduced the princess Europa and swam to Crete with her on his back. Only the forequarters are visible in the constellation, as it emerges from the waves.
In the shoulder of Taurus is the most famous open star cluster in the sky, the Pleiades, also known as the Seven Sisters.
The legend tells that the sisters were being chased by Orion and called out to Zeus to protect them. Zeus turned them into doves and placed them in the sky. In a Native American tale, the Pleiades are seven girls who are walking through the sky and get lost, never making it home. They remain in the sky, huddled together for warmth. The seventh sister is hard to see because she really wants to go home and her tears dim her luster. On a reasonably clear night you should be able to pick out six of the sisters. The whole star cluster actually has more than 500 stars, but it is possible to see as many as nine with the naked eye.
On the other side of Polaris from the Big Dipper is the striking W-shaped figure of Cassiopeia. (Careful not to mix this up with the Little Dipper.) This is the most prominent constellation in the winter sky, visible all year round in the northern hemisphere. If the Big Dipper is low in the sky then the W of Cassiopeia will be high. It is not as accurate in finding north but it does point in the general direction of the Pole Star.
In Greek mythology, Cassiopeia was the Queen of Ethiopia. The Romans saw her as being chained to her throne and placed in the heavens to hang upside down, for boasting that her daughter, Andromeda, was more beautiful than Aphrodite. Arab cultures pictured the constellation as a kneeling camel.
Finding your way around the night sky can be quite a challenge for the beginner. In this chapter we have described a few of the brighter stars and constellations from which you will be able to explore fu
rther. There are many good periodicals about astronomy that will open up the sky to you. The stories that surround our heavens are wonderful and colorful and as easy as reading a road map, with a little work!
Remember that all stars twinkle—the light shifts and flickers as you concentrate on it. Planets do not. If you narrow your eyes, you can see the disk of Jupiter even without binoculars.
Making a Paper Hat, Boat and Water Bomb
THERE IS SOMETHING ridiculously simple about these, but how to make them is something every boy should know. After all, with a little luck, you may one day have children of your own, and seeing a paper boat bobbing along on water is a pleasure.
THE HAT
First—the hat. The boat is just a few extra folds on the hat.
Fold a sheet of letter-sized paper in half, as shown.
Fold a central line in the half page and open out again.
Turn down the corners to that central line.
Fold one long strip up.
Fold over the corners on the dotted lines.
Fold up the other edge and you now have a paper hat—open it. This also works well with newspaper, but printer paper can be painted or colored. In theory, you don’t need to fold the corners over if you’re stopping at a hat—but we’re going on to turn it into a boat.
THE BOAT
The Dangerous Book for Boys Page 11
