Dear reader of my articles on WordPress ! I could easily imagine that you are sitting or lying casually somewhere and probably have a certain relaxing feeling ! Absolutely nothing could be further away from the current reality.
But be careful, because you are actually being whirled around in circles at this moment, because the earth is rotating, you are racing around the sun on the earth orbit, and you are racing through the cosmos with the milky way. We human beings behave like travellers on a spaceship called the Earth.
How does the Earth move in our solar system?
The most important movements of the earth are the daily rotation (also called spin) and the annual orbit around the sun, everyone should know these movements……..
The axis of the earth points all year round in the same direction (on Polaris)…….
…….it is the main star of the system, Polaris Aa, it is a supergiant and about 2000 times brighter than our sun. It’s about 430 light-years away from us. But Polaris Ab is a dwarf star, it orbits Polaris Aa at a distance of about 20 AU= 3 billion kilometers, it is about the distance of the planet Uranus from the Sun) within about 30 years in a retrograde (temporal or spatially distant) orbit.
…..and further……the average distance Earth-Sun is 1 AU or about 150 million kilometers. In one year our earth runs once around the sun with an average speed of 107,5 thousand km/h and the earth rotates therefore every day around its axis = (1 day).
The axis I am talking about is an imaginary connecting line from the North Pole through the centre of the Earth to the South Pole. So you, the earth rotates from west to east – if I would look from the north pole in counter-clockwise direction and from this we can conclude that the sun and stars in the east rise and set in the west. I can imagine that probably everyone of you has already experienced this and thus naturally recognized it that way. But another question : has anyone thought about the speed with which it rotates ? Because we cannot feel this rotation of the earth; it is a considerable rotational speed.
If you are not close to the North or South Pole or if you are living somewhere else, you are spinning around the earth’s axis with more than 1000 km/h – and that is faster than the cruising speed of most airplanes I know. But watch out, it gets even better, so while the earth rotates at the speed mentioned above, it naturally also orbits the sun at the same time. A short note about the distance of the earth from the sun, it is called astronomical unit (AE), you have surely heard of it, because it is about 150 million kilometers. We also do not feel these effects of the movement. But one thing I can say already now, this speed is more than impressive: And here it comes, truly at any time we race with more than
100 000 km/h around the sun.
That’s 100 times faster than a bullet can ever be and faster than any spacecraft ever launched. We know that the Earth’s orbit defines a plane, the plane of the ecliptic.
The axis of the Earth is inclined at 23.5 degrees to a line that is perpendicular to that plane. So this inclination of the Earth’s axis of rotation points almost exactly to the star Polaris, the North Star.
Please note that this axis inclination is only useful in relation to the plane of the ecliptic. Because the term „inclination“ itself has no meaning in space, because there is no absolute up or down. In space, „up“ and „down“ merely mean „directed away from the center of the Earth (or another planet)“ or „directed towards the center of the Earth“. Note, of course, that the Earth moves around the Sun in the same direction in which it rotates around its axis: counterclockwise when viewed from the North Pole. I am not talking about coincidence here. It is nothing other than a consequence of the way in which our planet was created. As I will report in one of the next articles, the Earth and the other planets were formed in a rotating gas cloud that surrounded our still young sun. The direction of rotation and orbit are therefore in the same direction in which this cloud rotated at that time.
How does our solar system move through the Milky Way?
But the rotational and orbital motion is only a small part of the movement of the spaceship Earth, which is on a long journey, within the Milky Way.
The local neighbourhood of our sun
Let’s start with the motion of our solar system within the local solar environment, i.e. the region where the Sun and its neighboring stars are located.
Let me just point out: this solar environment is just a tiny part (you can’t get any smaller) of the whole Milky Way (and this just made remark just points to the incredible size of the Milky Way….and please, let this stay in your memory forever.
Now a little easier explained : Imagine the smallest point you could draw in a DIN A5 picture of the Milky Way. Even if this point were 10 000 times smaller than the whole image, it would still cover a region that contains more than 10 million stars! (For calculate calmly : one ten thousandth of 100 billion stars of the Milky Way are 10 million stars).
We speak of a local solar environment when there is a region covering only between a few thousand and a few million of the nearest stars. The stars within the local solar neighbourhood (or the stars within any other small region of the Milky Way) move against each other essentially at random and also move quite fast. As an example, we move relatively to nearby stars at an average speed of about 70 000 kilometers per hour. This is more than three times the speed required by the International Space Station on its way around the Earth. In that case, would we really need to see the stars racing across the sky at such high speeds? But they do not! Or has anyone ever seen it? The reason for this is their huge distances from us.
You have probably also noticed that when a far away airplane seems to move slower in the sky than an airplane passing close by.
That is why the constellations do not seem to change. Nevertheless, in 10,000 years the constellations will be very different from those of today. In 500,000 years, they will no longer be visible. If you could watch a time-lapse movie spanning millions of years, you could really see the stars racing across the sky.
Of course, even stars are so far away that even at speeds of 70,000 km/h, their movements would only be visible to the naked eye if you observed them for a few thousand years.
Look at leaves floating in a river, their movements relative to each other are purely random, the same happens to the stars of the local solar environment. Now look very carefully, it becomes clear that all leaves are driven in the same direction by the current. Now take a careful look into the nearer surroundings of the sun, the seemingly random movement of the stars turns out to be a simpler and even much faster movement: For the entire Milky Way is therefore spinning.
At a distance of about 28 000 light years from the galactic centre, our solar system needs about 230 million years to orbit the Milky Way. Even if we could watch from outside, this motion would not be visible to the naked eye. But if you calculate the speed of our solar system on its orbit around the galactic center, you get a value of 800 000 km/h.
Very interesting for many of you is certainly the carefully made study of galactic rotation, because it reveals one of the greatest secrets of science. The stars at different distances from the Galactic center orbit the center at unexpectedly different speeds. By measuring these speeds, we can determine how mass is distributed throughout the galaxy.
The results obtained from such investigations were a big damn surprise: …….It seems that the stars in this galactic disk are only the tip of the iceberg compared to the mass of the entire galaxy.
This means that most of the mass of the Milky Way seems to be outside the visible disk, in the so-called galactic halo …..and we don’t know what this matter is made of, but it’s called dark matter, because it’s also known that it doesn’t emit light. This has naturally led to investigations of other galaxies and these have shown that they too are made up largely of dark matter. This mysterious matter must therefore exceed the normal matter of which planets and stars are made up many times over. And that’s not the end of the amazement: an even more mysterious dark energy seems to make up the largest part of the total energy content of the universe. Dear Amateur Scientists, I will also discuss the mysteries of Dark Matter and Dark Energy in a future article.
How do galaxies move through the universe?
Even the billions of galaxies in the Universe, which is overpowering for many, move relative to each other…….Within the Local Group, some galaxies even move towards us, others move away from us and at least two small galaxies (the Small and the Large Magellanic Cloud) orbit our Milky Way. And again I cannot avoid mentioning the speeds. Because these speeds are more than gigantic by earthly standards.
Example: The Milky Way moves with about 300 000 km/h in the direction of the Andromeda Nebula. Despite these high speeds we do not need to worry about a collision in the foreseeable future. Even if the Milky Way and the Andromeda Nebula were moving directly towards each other (which need not be the case), it would still take billions of years before the collision would start and then mankind would definitely not exist anymore !
However, if we take a look outside the Local Group, there are two astonishing facts that were first discovered in the 1920s by Edwin Hubble – the Hubble Space Telescope is named after him.
To 1. almost every galaxy outside the Local Group is moving away from us.
Re 2: The further away the galaxy is, the higher its speed.
This sounds almost as if we are suffering from a contagious cosmic disease, but there is a much simpler explanation: The entire universe is expanding (it is expanding). I will give more details about this later in more articles. But before I will give a small example : The following basic idea can be understood by a simple analogy. Let’s look at a raisin cake in the oven. Imagine you would like to bake a raisin cake. In the necessary dough the distance between adjacent raisins is one centimeter. But now you put the cake into an oven, of course it will inflate during baking.
After about an hour you take the cake out of the oven, which has inflated so much that the distance between adjacent raisins has increased to three centimetres…….and lo and behold, the expansion of the cake is quite obvious. But how would this process appear to you if you were to live in the cake as we live in the actual universe? Pick any raisin (any raisin); we’ll call it the Local Raisin and look at it in the cake before and after baking. For example, raisin 1 is 1 cm away before baking and 3 cm away after baking. So during baking it is two centimetres away from the local raisin. Its speed, measured from the local raisin, is therefore 2 cm/h. Raisin 2 moves from its initial distance of two centimetres to a distance of six centimetres after baking, so it has moved 4 cm away from the local raisin for one hour. Its speed is therefore 4 cm/h, i.e. twice as fast as raisin 1. In general, the expansion of the cake causes all raisins to move away from the local raisin, with raisins further away moving faster.
So Hubbles has discovered that galaxies move in a very similar way to the raisins in our cake, that most galaxies are moving away from us, and the further away they are, the faster it means that our universe is expanding in a similar way to the raisin cake.
If you now replace the Local Raisin with the Local Group and the other Raisins with more distant galaxies or clusters of galaxies, you will have a basic idea of how the Universe is expanding. Just as the dough expands between the raisins, the space itself expands between the galaxies. More distant galaxies move away from us faster because they are carried along by the expansion like the raisins in an expanding cake. At many billions of light-years away, we see galaxies that are moving away from us at almost the speed of light.
There is, however, an essential difference between the raisin cake and the universe: A cake has a center and edges, but the universe, to our knowledge, does not. Every being in any galaxy in the expanding universe sees exactly the same thing that we see: Other galaxies are receding and the more distant galaxies are receding faster. Because this impression is the same from any point in the Universe, no place can be more „central“ than another. The fact that the Universe has no center and no edge may seem strange and cannot be easily illustrated. However, as you will see in my contributions, space and time do not necessarily correspond to your usual conception.
Einstein showed that the three dimensions of space – length, width and height – are connected to a fourth dimension, which we perceive as time. Once you have learned to view the universe as four-dimensional, its centerlessness and lack of edges will not seem so strange. We must realize that, unlike a raisin cake, Hubble could not directly see how the galaxies move with time – the distances are too great to see any movement during a human lifetime. Instead, he determined the speed of the galaxies by fanning their light into a spectrum and observing something we call the Doppler shift. We still use the same technique today, which shows how much modern astronomy depends on both careful observation and today’s understanding of the laws of nature.
Do we ever stand still?
As we have seen, we never stand still. We rotate around the Earth’s axis at more than 1000 km/h, while our planet revolves around the sun at more than 100 000 km/h. Our solar system moves at a typical speed of over 70 000 km/h between the stars of the local solar environment and simultaneously orbits the galactic centre at a speed of over 800 000 km/h. Our Milky Way is moving between the galaxies of the Local Group, while all other galaxies are moving away from us at speeds that are increasing with distance in our expanding universe. So spaceship Earth is taking us on an extraordinary journey.