النجوم وأطياف ضوئها .. كتاب في سبيل موسوعة علمية .. الدكتور أحمد ذكي

Stars and their light spectra

A physics student, in his high school or at university, passes a ray of white light through a three-sided glass prism, and this ray emerges from the other side, and it is decomposed into several colors, from red, to orange, to yellow, to green, to blue, to... Indigo to violet, this is the familiar light spectrum.

And the light spectrum that we get from the star
He gives us a lot of news about this star. Light is the only thing that connects us to the star, and the star connects us, and the spectrograph analyzes this light and reveals a lot to us about the state of the star.

From that, it tells us about the temperature of the star, how much it is. It tells us about the structure of a chemical star, what it is...
It tells us whether the star has an atmosphere surrounding it, like the sun, or not.
He tells us about the magnetism of the star, whether he has any luck with it or not.
It tells us about the starlight...how much it is. And about its color, what is it? All of this paves the way for us to unite the families of stars together, sometimes in harmony, and sometimes in disagreement, distance and proximity to us.

How far does this world extend? And where does he stand?
We built the deficit.
If we destroy those devices that we call...
(With spectroscopes, or spectrographs, spread in all the observatories of the world, and the devices that have developed into them, then we will stop knowing the science of the sky, the science of astronomy, forever.)

The stars are in constant motion:

There is no one among us who does not know the stars with comets, including the famous Halley’s Comet, which was named after him because this astronomer discovered it. He is the culprit about whom Abu Tammam said in the past:

They frightened people with dark cunning
If the western planet with a tail appears

This learned man was the first man to corrupt people
As long as they were not aware that the stars were fixed in the sky, as if they were hanging lanterns that would not move from their place, Halley revealed in the year 1718 the position of the star known as Sirius, which is the brightest star in the sky, and proved that it had shifted from its position which had been proven to him by the famous ancient astronomer Ptolemy, the Alexandrian citizen. Who lived in Alexandria in the second century AD. Halley revealed that the star Sirius moved over a period of time of about 15 centuries, by an amount that appears in the sky by the same amount that the disk of the moon appears to its observer when it was complete and became a full moon.

You ask: How long is the distance you move? Of course, it is a huge, huge distance if we consider the distance of Sirius from us.

The star is farther away from us, so our awareness of its movement becomes less, for it is a relative movement that appears over the patch of sky in which the star is moving, and behind it are stars that are farther away from it, and much farther away, to the point that we do not feel any movement or shifting in them. For us, they are considered fixed, through which we detect the movement of the stars that are closer to us. Attributed to those distant ones that we did not find any reason to consider as fixed.

This movement that we detect by comparing the star to the fixed, distant stars behind it is called, in our terminology, the Proper Motion of the Star.

But there is another movement that reveals the state of the star.
In terms of its proximity to us, or its distance from us. That is, the speed of the star in the line of sight from us to it. We detect this from the spectrum that we obtain from the light of this star, based on a phenomenon discovered by scientists, which is:

If the lines in the star's spectrum are compared to the normal light spectrum, I find that they shift toward the violet end. This indicates that the star is approaching us. If you find that it is shifting towards the red end, this indicates that the star is moving away from us.

We cannot go into more detail about this. The goal is that this phenomenon has greatly benefited us in knowing
The stars approach and move away from us.

By this phenomenon, we know that the sun (as it moves led by its north pole towards a special part of the sky) is approaching it and the stars of the sky that are heading towards it are competing for it. As for the stars behind it, they move away from it.
And another thing we knew from that phenomenon: that the stars

It rotates around its axis. This is because as the star rotates, its right side moves away from us, for example, and therefore its left side approaches us. We deduce this from their spectra. So the star rotates on its axis. We know in which direction it rotates, clockwise or counterclockwise.

(There are some stars that explode, and in their explosion, they eject huge amounts of their matter, and they are ejected with such force that they move away from the position of the star at a speed that may reach thousands of miles per second. An example of this is what we see in the sky today and we call it the Crab Nebula.
The Crab Nebula is one of the nebulae known as Super Nova, meaning extremely luminous stars. This nebula was observed by the Chinese in the year 1054 AD.)

When talking about movement, we should not forget the movement of our galaxy, the one in which our sun is one of the stars.
This galaxy, with its stars, which in terms of mass amount to about 100,000 million suns, revolves around its axis and completes its cycle in about 200 million years.

(To know the movement of the star, whether it is approaching us, or moving away from us, we take a photograph of its light spectrum with observatories. Then we compare it with the normal spectrum. We see how much the lines of the star’s spectrum have shifted from their positions. If the shift is toward the violet end, then the star is approaching. If it is toward the end. If the star is red, the star is moving away. In the upper comparison, the star shifts to the left (to the violet side), and in the lower comparison, the other star moves to the right (to the red side). From the amount of the shift, the amount of the star’s approach or distance is calculated.