Earth is the fifth largest planet in the system. It has a magnetic field and a liquid nickel-iron core.
ROTATION AROUND THE SUN (Earth year): 365.25 days.
It has an elliptical orbit that means the Sun–Earth distance varies from 91 to 95 million miles at different times. The Earth rotates on the same plane as nearly all of the other planets in the system (except for Pluto), as if they are imbedded in the surface of an invisible plate. Very neat. We call it home.
MOONS: One, which rotates around the Earth in 27.3 days. With an astonishing lack of imagination, we call it “The Moon.” (This is a bit like the London Times calling itself The Times because it was first, while all other Times newspapers include a city—the Boston Times, the New York Times, and so on.)
MARS
Fourth planet from the Sun, at an average of 141 million miles (226 million km).
GRAVITY: One-third that of Earth’s.
No significant magnetic field, which suggests the core is now solid, though it may have been liquid in the past.
ROTATION AROUND THE SUN: 686.98 days.
AVERAGE TEMPERATURE: –55°C (–67°F).
Mars has ice caps at both north and south poles, made up of water ice and frozen carbon dioxide. It has an atmosphere of 95% carbon dioxide, 3% nitrogen, and 2% argon and trace gases. Like Earth, it is tilted on its polar axis and experiences seasons, which can involve ferocious dust storms. Despite various probes and landings, we have yet to set foot on the red planet.
MOONS: Two, named Phobos (Fear) and Deimos (Panic). Mars was named after the Roman god of war. The Greek version of Mars was the god, Ares, who had two sons. The moons are named after them.
JUPITER
The fifth planet from the Sun, at an average: 484 million miles (778 million km).
Jupiter is by far the largest planet in the solar system and the fourth brightest thing in our sky, after the Sun, the Moon, and Venus. It takes twelve years to orbit the Sun. It is sometimes called the amateur’s planet, because it can be found easily with a basic telescope, or even binoculars.
We haven’t been to Jupiter and we probably never will—so our knowledge is based on observation and the occasional orbiter and probe. Science means we are not blind, however. For example, an effect of gravity is that it causes a passing object to accelerate, which is why you will occasionally see film sequences of spaceships using a “slingshot around the Sun” effect. The increase in speed can be measured and compared to other figures we already know. Piece by piece, we build up a picture of a planet—even one where the pressure and gravity is so crushing that we are unlikely ever to ever get a probe down to the surface.
Jupiter’s mass can be predicted from its effect on its moons—318 times that of Earth. However, if Jupiter were hollow, more than a thousand Earths could fit inside, which means it must be composed of much lighter gaseous elements. This was confirmed by the Galileo probe in 1995, which dropped into the outer reaches of the atmosphere and found them composed of helium, hydrogen, ammonia, and methane. In many ways, Jupiter is a failed sun—80 times too small to ignite.
Beneath the gas layers, pressure increases to more than 3 million Earth atmospheres. At that level, even hydrogen has properties of a metal and Jupiter has a solid core that must be one of the most hostile places imaginable. Winds there will range up to 400 mph and at those pressures, the chemistry of the universe that we think we understand will be completely alien. At temperatures of between –121 and –163°C (–186 to –261°F), ammonia will fall as white snow.
MOONS: Around 61, with a faint ring of debris. There are hundreds, perhaps thousands, of rocks orbiting Jupiter. Whether they are referred to as moons or not is a matter of opinion. Galileo discovered the four largest in 1610. They are: Io, Europa, Ganymede and Callisto. Given their size, they deserve a special mention. They are named after lovers of the chief god of the Greeks, Zeus, whom the Romans called Jupiter. Io. The closest to Jupiter, pronounced “EYE-oh.” It has a diameter of 1,942 miles (3,125 km), a little less than the Earth’s moon. It is intensely volcanic and its closeness to Jupiter’s magnetic field generates three million electrical amps that flow into Jupiter’s ionosphere. It orbits Jupiter in 1.77 days, at a distance of 220,000 miles (354,000 km).
Europa. The smoothest object in the solar system. It takes 3.55 days to orbit Jupiter. Its surface is ice, but a weak magnetic field of its own may indicate that there is liquid salt water below the surface. It has a diameter of just over 1,961 miles (3,155 km). Europa orbits Jupiter at a mean distance of 420,000 miles (670,000 km).
Ganymede. The largest moon of Jupiter and the largest moon in the solar system, with a diameter of 3,400 miles (5,471 km). It orbits Jupiter at a mean distance of 664,000 miles (1,068,000 km), taking 7.15 Earth days. Ganymede is larger than Mercury.
Callisto. The last of the Galilean moons. It has a diameter of 3,000 miles (4,828 km) and orbits at 1,170,000 miles (1,880,000 km) from Jupiter. It is similar in size to Mercury and orbits in 16.7 Earth days.
SATURN
The sixth planet out from the Sun, at 856 million miles (1,377 billion km).
Like Jupiter, it is a gas planet, with atmospheric pressure condensing hydrogen into liquid and even metal toward the core. Still, we think the overall density would be low enough for Saturn to float on water. It takes 29.5 years to orbit the Sun.
ATMOSPHERE: composed of 88% hydrogen, 11% helium and traces of methane, ammonia and other gases. Wind speeds on the surface are more than 1,000 mph (1,600 kph).
The rings stretch out more than 84,000 miles (135,000 km) from Saturn’s center. They were first seen by Galileo in 1610, though he described them as handles, as he saw them end on. The Dutch astronomer Christiaan Huygens was the first to recognize them as rings, separate from the planetary surface.
TEMPERATURE: –130°C (–202°F) to –191°C (–312°F). (Very cold!)
MOONS: Quite a large number if you count very small pieces of rock, but there are fifteen reasonably sized moons, ranging from Titan, the largest (second only to Ganymede in the solar system and even possessing a thin atmosphere), down to Pan, which is about 12.5 miles (20 km) across. The NASA probe Huygens landed on Titan in 2005.
Saturn is the Roman name for the Greek god, Cronus, who was father to Zeus.
URANUS
The seventh planet from the Sun, at an average distance of 1.78 billion miles. (2.86 billion km).
It has 11 rings and more than 20 confirmed moons, though as with Saturn and Jupiter, there are probably many more we haven’t spotted yet. It is 67 times bigger than Earth, but has a mass only 14.5 times that of Earth, qualifying it for gas giant status, though on a smaller scale to Saturn and Jupiter.
The space probe Voyager 2 reached Uranus in 1986, our only source of knowledge at the time of writing, apart from Earth observation.
ROTATION AROUND SUN: 84 Earth years, though it spins on its own axis even faster than Earth—17.25 hours.
Uranus has an atmosphere of 83% hydrogen, 15% helium, and 2% methane. The planet core is nothing more than rock and ice. It has a huge tilt on its polar axis, so that one pole then the other points at the Sun. This means each pole receives sunlight for 42 Earth years. Average temperature: –197°C (–323°F) to –220°C (–364°F).
MOONS: 27. All named after Shakespeare characters, with names like: Cordelia (closest), Ophelia, Bianca, Puck, Rosalind, Desdemona, and so on.
In mythology, Uranus was the father of Saturn, grandfather to Zeus/Jupiter.
NEPTUNE
The eighth planet from the Sun at 2.8 billion miles (4.5 billion km).
Neptune is the fourth largest in the system. It has four rings and eleven known moons. It is the last of the gas giant or Jovian planets—seventy-two times Earth’s volume, seventeen times its mass.
It is believed to be composed of ice around a rock core, under an atmosphere of hydrogen, helium, and methane.
Every 248 years, Pluto’s erratic orbit brings it inside the “shell” of Neptune’s orbit,
making it the farthest planet from the Sun for a twenty-year period. The last time this happened was from 1979 to 1999, when Pluto moved back out. Neptune is the last of those planets that orbit on the same flat plane as Earth.
The existence of Neptune was predicted before it was seen, like Halley’s Comet. The orbital track of Uranus seemed to be affected by the gravity of a large mass. The path and location of that mass were mathematically plotted, then searched for—and Neptune was found. It was first observed in 1846.
The only vehicle from Earth to reach Neptune was Voyager 2, in 1989.
ROTATION AROUND THE SUN: 164.79 Earth years. It has an axial tilt of 29.6° compared to Earth’s 23.5°, suggesting it has a similar movement of seasons, though to be honest, it’s so cold, you’d hardly notice, or care.
PLUTO
Distance from the sun: 3.65 billion miles (5.87 billion km).
Pluto is what happens when a stray lump is slowly drawn in to an orderly solar system. In 2006, a group of astronomers declassified Pluto as a planet. However, it will always be a matter of opinion. As far as we are concerned, two things matter: Pluto is big enough to have spun itself into a sphere at some point in the unimaginably distant past—and it has an orbiting moon, called Charon. That makes it a planet.
Pluto is large enough to affect on the orbits of Neptune and Uranus. It is so small and distant that, even knowing it was there, it still took the telescopes of the world 25 years to find it for the first time in 1930. It took until 1978 for anyone to spot the single moon.
We haven’t managed to get a probe out that far, but the Hubble telescope has mapped 85% of Pluto’s surface. It has polar caps and seems to be a ball of rock and dirty ice. It does have a thin atmosphere of nitrogen, carbon dioxide, and methane.
Being a dark and miserable place, Pluto was named after the Roman god of the Underworld (Hades to the Greeks). Charon was the boatman who ferried the souls across the River Styx.
SEDNA—BUT IS IT A PLANET?
In 2004, Dr Mike Brown of the California Institute of Technology announced the discovery of another planet—one about three-quarters the size of Pluto, more than 8 billion miles (13 billion km) away from the Sun. Sedna is reddish-colored, has no moon, and its classification as a planet is looking extremely unlikely, especially with the current debate over Pluto.
AND FINALLY, COMETS, ASTEROIDS, AND OTHER DEBRIS . . .
The Sun is such a massive object that its gravity affects a vast volume of space, trapping objects such as Halley’s Comet. These tend to be dirty balls of ice, sometimes just a few miles across. Halley’s was large enough to have an effect on the orbital paths of the system and Edmund Halley’s achievement is that he predicted this mathematically without seeing the comet. In fact, he never saw it. It wasn’t until sixteen years after his death, in 1758, that sky watchers on Earth saw the comet once more. It is visible from Earth every 75–79 years and has been recorded since 240 BC. The next appearance is in 2061. It is extremely unlikely that the authors of this book will see it, but there is a chance you will . . .
The inner asteroid belt lies between the orbits of Mars and Jupiter. It is composed of hundreds of thousands of rocks varying in size from grains to large ones hundreds of miles across. It may be debris from a planet-sized collision, or just the building blocks of the system, left over after everything started cooling.
Meteors reach the system as it travels in space on the end of the Milky Way galaxy. They are usually made of stone silica, more rarely iron or nickel or a mixture of all three. They can make a bright trail as they reach the Earth’s atmosphere and hit friction. If they don’t burn up, they can hit the planet below with more force than an atomic bomb—but that almost never happens. (See Dinosaurs.) The best time to look for them is August 9–16 and December 12–16. Meteors in the summer shower are known as the Perseids, as they appear in the constellation of Perseus. At its height, one a minute can be seen. Meteors in the winter meteor shower are known as the Geminids, as they appear in Gemini, near Orion. Both showers should be visible even from urban locations. They won’t last forever—the Geminids only came into existence in 1862.
That’s it. The rest is space and cosmic radiation.
The Ten Commandments
WHAT COMPILERS of modern versions of the Bible sometimes fail to appreciate is that the language of the King James Version has a grandeur, even a power, that their versions simply lack. It is no hardship to “walk through a dark valley.” On the other hand, “the valley of the shadow of death” is a different matter. Frankly, the rhythm and poetry are part of the effect and not to be lightly cast aside. We can find no better example of this than the Ten Commandments themselves. Book of Exodus, Chapter 20, Verses 1–17:
And God spake all these words, saying, I am the Lord thy God, which have brought thee out of the land of Egypt, out of the house of bondage.
Thou shalt have no other gods before me.
Thou shalt not make unto thee any graven image, or any likeness of any thing that is in heaven above, or that is in the earth beneath, or that is in the water under the earth: thou shalt not bow down thyself to them, nor serve them: for I the Lord thy God am a jealous God, visiting the iniquity of the fathers upon the children unto the third and fourth generation of them that hate me; and shewing mercy unto thousands of them that love me, and keep my commandments.
Thou shalt not take the name of the Lord thy God in vain; for the Lord will not hold him guiltless that taketh his name in vain.
Remember the sabbath day, to keep it holy. Six days shalt thou labor, and do all thy work: but the seventh day is the sabbath of the Lord thy God: in it thou shalt not do any work, thou, nor thy son, nor thy daughter, thy manservant, nor thy maidservant, nor thy cattle, nor thy stranger that is within thy gates: for in six days the Lord made heaven and earth, the sea, and all that in them is, and rested the seventh day: wherefore the Lord blessed the sabbath day, and hallowed it.
Honour thy father and thy mother: that thy days may be long upon the land which the Lord thy God giveth thee.
Thou shalt not kill.
Thou shalt not commit adultery.
Thou shalt not steal.
Thou shalt not bear false witness against thy neighbor.
Thou shalt not covet thy neighbor’s house, thou shalt not covet thy neighbor’s wife, nor his manservant, nor his maidservant, nor his ox, nor his ass, nor any thing that is thy neighbor’s.
Verses 18 and 19:
And all the people saw the thunderings, and the lightnings, and the noise of the trumpet, and the mountain smoking: and when the people saw it, they removed, and stood afar off. And they said unto Moses, Speak thou with us, and we will hear: but let not God speak with us, lest we die.
Common Trees
IF YOU HAVE ever hiked through a vast American forest, you might wonder at the fact that just a century ago, a lot of states had less than half the woodland they have now. The natural environment in temperate regions does favor trees, but human activity does not. Still, though we have to keep working to preserve our national forests and parks, hardwoods (like maple and pine) and conifers (think Christmas trees) cover the country. Fire and ax cleared a lot of ground in the preceding centuries, but over the years, the young trees have managed to regain at least some of their former grandeur.
To our ancestors, forests were an essential part of the rural economy, providing timber for houses, animals to trap, charcoal for fuel, and wild mushrooms and herbs. A system evolved called “coppicing,” where an area of undergrowth and small trees was grown for periodic cutting and managed like any other crop. It is a good idea to know the common trees and how to identify them, since it is as important to understand the earth around you as it is the heavens above. Such knowledge might even be useful when it comes to making things from wood.
RED OAK (QUERCUS RUBRA)
Oak trees have been considered sacred by people throughout the ages, from the Greeks and Romans to the Christian Church. These trees are especially prone to
being hit by lightning, even when they are surrounded by other trees: an oak tree is ten to twenty times more likely to be hit than a beech tree, even if it is surrounded by beeches. When an oak tree is hit by lightning, it will likely burst into flame. An oak, if not felled by man or nature, can live for 200 to 300 years.
Bark: When young, gray and smooth. As the trees age, the bark develops flat ridges that are separated by fissures.
Leaves: Longer in length than width; curve between lobes.
Buds: Shiny, reddish-brown, pointy.
SUGAR MAPLE (ACER SACCHARUM)
This is the state tree in Vermont, New York, and New Hampshire—and it was favored by the ancient Romans, too, who used shafts of the wood to make their spears. The sugar maple is particularly beloved nowadays for its sweet sap, which has been poured liberally atop many a breakfast pancake. Each spring, a sugar maple produces 1 to 8 pints of sap. It can take forty pints of sap to make one pint of maple syrup.
Bark: Gray and dark with long, flat ridges that curl out in one direction.
Leaves: Wide with a U-shaped space between two lobes and three main veins. Smooth edges. The leaves grow in opposite pairs on the branch.
Buds: Reddish-brown and pointy.
SILVER BIRCH (BETULA PENDULA)
Silver birch is not native, but commonly planted in dry and sandy soils. Fast-growing, they rarely last longer than 100 years. At maturity, they can reach 100 ft (30.5m). Distinguished by stiff branches and dropping twigs. Spring sap can be tapped into bottles and tastes like clear, sugary water. However, if the hole is left unplugged or too much is taken, the tree will die.
The Dangerous Book for Boys Page 25
