The Space Journey
Page 6
The Milky Way is often visible in the night sky as a faintly glowing band of stars. You can spot Andromeda without binoculars as well, but only as a dim speck of light that looks like a star.
All galaxies do not look like the Milky Way with its spiral arms. In some, for instance, the stars are gathered in the form of a squashed ball.
Well then, how many galaxies are there? Actually, nobody knows. Maybe they are infinite in number. But in the part of the universe that is visible to us from Earth, there are probably a couple of hundred billion galaxies.
14. Black holes
Black holes are some of the strangest things in space. They are called black holes because their force of gravity is so strong that not even light can get out of them. (“Hey, wait a minute!” says an alert reader now. “Earlier – under point 5 – you said that light particles don’t have any mass; then, how can the force of gravity have an effect on them?” Well, Newton wasn’t altogether right in his explanation of the force of gravity and Einstein did some revisions with his general theory of relativity; this shows that even massless particles are affected by extremely heavy objects.)
Black holes might be created when large stars die, that is, when their fuel runs out and the only thing that remains of them are ashes. At that moment, all the ash collapses, it is contracted by its own gravitational force, and the force can be so enormous that nothing can resist it. All of the large star’s ashes are eventually gathered into one small dot. The force of gravity in its vicinity is so strong that nothing that comes too close can get away. (Our own Sun isn’t big enough to become a black hole when it dies.)
At the centre of many galaxies, there seem to be huge black holes. It is almost 100 per cent certain that there is such a gigantic black hole at the centre of the Milky Way. It weighs several million times more than our Sun!
But how do you discover a black hole then? Well, around the hole spins a tremendous amount of small objects that react and create light and other particles, which we are able to see from Earth. With the help of calculations we have come to the conclusion that they must originate from a black hole.
If you would look at a rocket that went into a black hole, it would seem as if the time aboard the rocket went slower and slower and would eventually stop. But for those who were inside the rocket, time would pass at the same rate all the time. However, the rocket would pretty soon be crushed by the enormous gravitation that exists close to the centre of the black hole.
It is not yet known exactly what happens inside a black hole. Perhaps it takes a new Einstein or a Newton to explain it. Nevertheless, certain scientists speculate that there could be some sort of connection between different black holes in the universe; and, that this might be an avenue to “jump” from one place in the universe to another - even to move about through time. It is, nonetheless, so unlikely that almost no one really believes that this really works. So it is pure fantasy when Uncle Albert steers his rocket through the black hole and comes out much earlier in time. As a matter of fact, once you have passed the border of a black hole - the Schwarzschild radius - there’s no turning back and soon your time is up.
15. Centrifugal force
Everybody knows that you can tie something to a string, for example a conker, and then spin it round and round with your hand or your arm. It’s as if there’s a force dragging the conker outwards, away from your hand. The phenomenon is called centrifugal force and comes from the spinning itself. It is also the same phenomenon you experience in cars that turn quickly where you are pushed to the side - or on a merry-go-round.
16. Continental Drift - the parts of the world are moving
If you look at a map you will easily see the Earth’s separate landmasses surrounded by sea: Europe, Asia, America, Africa, Australia and the Antarctic. They are also called continents. In former days it was considered obvious that they were located where they were, and that they had always been in the same place. So when a scientist, Alfred Wegener, in 1912 claimed that the continents might be moving in relation to each other, he was almost thought to be a bit nuts. But the reason for his claim was, among other things, that if you look at the Atlantic Ocean it looks as if especially South America and Africa fit together just like pieces of a jigsaw puzzle. And, as time went by, it was shown that Wegener was right. The surface of the Earth is like a rough shell covering a fluid interior. The skin cracks sometimes and separate parts (continents) float about and occasionally they run into each other – causing mountain chains. Volcanic eruptions and earthquakes are results of this movement, as well.
About 225 million years ago, all the Earth’s landmasses weregathered in a gigantic continent called Pangaea (1). Later Pangaea broke up in severalparts. 65 million years ago (2), today’s continents (3) started to take their forms. Ho¬wever, you can see clearly that, among other things, the Atlantic Ocean was much narrower than today.
But this does not happen quickly. The parts of the world usually move just a few centimetres every year. Nevertheless, during 65 million years they have had time to move thousands of kilometres.
17. Dark Matter
The term dark matter means objects in space that have weight – thus they have mass – but which in no way are able to emit light; no type of light at all (point 8). It is however, not black holes we are talking about, but something else. Calculations of the galaxies’ movements and other phenomena, indicates that there is much more matter in the universe than we are able to see by means of the light that reaches us; in fact, about four times as much. This means that we cannot see most of the matter that exists in the universe, and we don’t even know what it is! But there are theories. The most frequent suggestion is that it is some type of miniscule particle, about the same thing as the protons, neutrons and electrons mentioned under point 1.
18. Dinosaurs and flying reptiles
Dinosaurs lived on Earth between 230 and 65 million years ago. They were the most important land animals of all, for 160 million years, until they suddenly died out. Some were gigantic, others not bigger than chickens. There were carnivores, peaceable herbivores, some quadrupeds, others bipeds, some with body armour, others with horns and so on. Some dinosaurs lived in flocks. Over 500 different species of dinosaur have been discovered, and it is believed that there have been about two thousand species.
The biggest dinosaurs of all were the sauropods. One of these was formerly known as the Brontosaurus [“thunder lizard”], known nowadays by the proper scientific name Apatosaurus (“deceptive lizard”). But the “Bronto-apato” lived 154 – 140 million years ago, so it couldn’t have been the type of animal that Markus and Mariana met. Perhaps it was some other species of sauropod which hasn’t been discovered yet. The biggest dinosaur known nowadays is Puertasaurus, which is estimated to have been up to 40 meters long and have weighed well over 100 tons.
A giant dinosaur, which did live at the end of the age of the dinosaurs, was Tyrannosaurus Rex, (“Tyrant lizard king”). It was 14 to 15 meters long, about 5 meters tall and may have weighed up to 10 tons. The head could have been up to 1, 5 meters long with some of the largest teeth known: 15 centimetres long. A Tyrannosaurus probably could have swallowed a human adult whole.
Ostrich dinosaurs lived at the end of the age of the dinosaurs, as well. They are called this because they somewhat resembled ostriches. They walked on their hind legs and had small short forelimbs. The hip height was about one and a half meters and they could run very quickly, perhaps up to 80 km/h over shorter distances.
Flying reptiles, or pterosaurs, were not dinosaurs even though they lived during the same period and died out at the same time. One of the largest was Quetzalcoatlus with a wingspan of 10 to 11 meters.
19. The Yukatan-asteroid and the extinction of dinosaurs
About 65 million years ago something dramatic occurred on Earth that led to the disappearance of two thirds of all the existing animal groups at that time; and, of the larger animals (over 25 kg) at least 90 per cent vanished. Among those were
all of the dinosaurs; almost anyhow. There is a lot that indicates that today’s birds are descended from early dinosaurs (and thus not from the flying reptiles); if that is the case, at least some descendants of dinosaur animals must have survived.
The most accepted explanation for the disaster is that a gigantic rock from space, an asteroid or a comet (at least 10 kilometres in diameter) collided with Earth 65 million years ago. Clear traces have been found of an impact site from that time in the Gulf of Mexico, off the Yucatan Peninsula – the Chicxulub Crater. When the asteroid/comet crashed into the Earth there must have been an explosion equalling the force of several million of the most powerful bombs ever made. It is believed that the explosion triggered gigantic global wildfires. The soot from these and all the dust from the explosion are said to have effectively blocked out the sunlight for many months, perhaps even years. It is easy to understand that many animals had great difficulties surviving this, and above all, it was the larger animals that suffered and died out. But some small mammals pulled through and, as time went on, they became the most important land animals on Earth. We humans, who are mammals as well, have evolved only recently – during the last million years.
Table of Contents
The Space Journey
Foreword
Kapittel 1
Kapittel 2
Kapittel 3
Kapittel 4
Kapittel 5
Kapittel 6
Kapittel 7
Kapittel 8
Kapittel 9
Kapittel 10
Kapittel 11
Kapittel 12
Kapittel 13
Fact and Fantasy