In ancient times, they came to have the idea that the universe was just the Earth, and perhaps it looked like a huge place because they had no means of transportation to help them travel great distances. Aristotle proposed that the Earth was the center of the universe and that it was surrounded by the Moon, the Sun, the planets and a black sphere with perforations, better known as stars, which allowed us to see a hidden fire.

Stories told through a legend are known as cosmogonies, which are undoubtedly fantastic explanations of the origin of the universe; However, in addition to the origin of the whole, there are factors that interest humanity, such as the carrying out of space expeditions, which allow them to leave the atmosphere and reach outer space.

In the universe, especially on planet Earth, distance, mass, volume, density and temperature can be measured.

Planet Earth has its own measurement units, like the examples just cited, but in the universe, star brightness, declination, wavelength, and some other magnitudes are also measured.

Who tried to measure the universe in the first instance was Archimedes of Syracuse. He wanted to calculate how many grains of sand would fit in the cosmos, from that idea, it was necessary for him to measure the cosmos, through the model of Aristarchus of Samos, who was the first to place the Sun and not the Earth. the center of the universe, that is, the heliocentric model of the solar system.

Archimedes, he kept imagining that the limit of the universe was a sphere with fixed stars, since he didn't have the instruments to detect that they were moving at different speeds. So, using angles and mathematical calculations, I came to the conclusion that the universe must measure about 100 billion stadia or 19 billion kilometers, or as scientists mention 2 light years, for example, the closest star to the Sun, " Proxima centauri" is at a greater distance, approximately 4.2 light years.

Light years are the distance in space that an object, or in this case a star, is from the Earth or place in the universe.

To understand the size of the universe, start with something more familiar, Earth, its diameter is about 12,000 kilometers. In turn, the Earth is part of the solar system that measures approximately 4,500 million kilometers.

The solar system is part of the galaxy called the Milky Way, which turns out to be 10,000 times larger and measures 500 billion kilometers at its longest part, approximately 50 light-years, in fact, in 1920 astronomers considered that the stars were contained in the Way. Milky, but with studies of the universe and technological advances, they discovered that other galaxies existed. In the 90s the Hubble telescope managed to photograph an image, in which each bright spot is a galaxy that contains its own stars and planets, on the other hand, the Milky Way where our solar system is is like that. Image.

Therefore, we are very small, almost as if we were an atom, represented by a galaxy. However, the Milky Way is part of a family called the local group, which contains about 50 galaxies and is estimated to have a diameter of 10 million light years and still belong to the immense Virgo cluster.

Therefore, the universe is bigger than we could imagine and we represent a very small part, but

Why is it measured in light years?

To understand this unit of measure, just make the following statement: a year has 365, that is, the year is a unit of time. At some point you've heard of light years, to know how many days are in a light year, you'll be surprised to learn that the light year isn't used to measure time, it's used to measure distances as well as specific units are used to measure little things, the light year is used to measure astronomical distances. On the other hand, the speed of light is exaggeratedly fast, for example, a photon of light travels a distance of 300 million meters per second, if you could measure the speed at which light leaves a laser, you would get a value of 300 million per second, so if a photon of light has traveled for a year, it travels 9 trillion 460 thousand 730 million 473,000 kilometers, that amount is the equivalent of one light year.

These are very long distances to travel that, if you were to travel that distance at the average speed of a car, it would take many years to travel.

Now that you start measuring distances in the universe, there are variations in distances, such as light-hour, light-minute and second light, the latter is the distance that light travels in one second, for example, the Earth is just over 384,000 kilometers from the Moon; Light reflected from the Moon takes just over a second to reach Earth, so the Moon is said to be 1.3 light seconds from Earth, it takes 8.3 minutes for the Sun's light to reach Earth and it is said Since the Milky Way has a diameter of 100,000 light years, these measurements are approximations.

There are different ways to measure the universe, one of which is star brightness or stellar magnitude, for example, ancient Greek astronomers called first-size or first-magnitude stars the brightest stars that appeared after sunset. And the last ones that appeared. disappeared after sunrise or sunrise, the magnitude scale is considered from magnitude 1 to magnitude 6. Where magnitude 6 is the weakest star to the naked eye and magnitude 1 corresponds to the brightest star.

So, according to stellar magnitude, you could say that the brightest star is because it's located closer to Earth, but that could be relative, as it actually depends on proximity and size, the brighter a star. moves away and changes to a red hue, for example a neutron star, due to its bright characteristics due to its own radiation, can be very far away and glow even though it is dying.

The brightness of a star doesn't always depend on how far it is from the Earth, so how do you know how far away the stars are?

Measuring these astronomical distances seems impossible and has been for a long time; For example, if on a clear night you look at the sky, it will look like all those points of light are at the same distance, like a vault, if you repeat this observation for many days in a row, you will notice that some of these points change position in relation to other stars. The ancient astronomers or sky watchers noticed this and called the restless stars planets, meaning "wanderers."

Everything is based on observation, so they imagined that the Earth was at the center of the universe, with the Moon, Sun and stars revolving around it and the rest of the stars all at the same distance. . Now, it is known that this is not the case and the stars are at different distances, but how do scientists or astronomers determine these distances?

Two techniques are used: the first is called parallax, this method is very similar to how close distances are distinguished on Earth, this is due to the fact that we have two eyes. To understand this concept, do the following exercise.

Exercise: parallax

Parallax is the change of movement of the observer's vision, to understand how it works, extend your arm a little forward and lift your thumb, now look at the thumb alternating eyes, first with the right eye closed and then with the left one closed, Repeat this exercise a few more times, increasing the speed of opening and closing your eyes.

Now bring your finger a little closer to your face and repeat the action of opening and closing your eyes a few more times.

What did you notice?

When you close one eye and open the other, your finger seems to move from side to side in contrast to the more distant objects in the background, so does the star you want to know your distance from, will be seen in a different position depending on, If you see it when the Earth is at one point in its orbit, for example, in summer, or at another point in the same orbit, maybe in winter.

Thus, the way in which one can know the distance that exists between a star and the Earth, depends on carrying out the observation in two of the different seasons of the year to know exactly its distance. This occurs when one observes that the Moon is sometimes seen closer to the Earth and other times it appears to be much more distant, also changing in size due to its relative position.

The distance between Earth, Sun and observation gives the angle to calculate the distance to the star and a trigonometric operation is used.

However, there are stars where their angles are very small or indistinguishable, it is even very difficult to measure and this makes it difficult or impossible to know how far away the star is. This is what limits this "parallax" technique, for that there is another alternative.

In science there are different alternatives to perform calculations, that when a method is limited, there is another with greater amplitude that will allow it to be done; for example, the parallax system only works on stars that are less than 400 light-years away. For more distant stars, the technique used is the relationship between the color and brightness of the stars.

By studying nearby stars, especially some with very peculiar characteristics known as standard candles, it is determined that a certain star color corresponds to a certain brightness or absolute magnitude, seen at a distance of 10 parsecs. The calculation of the distance is carried out with more advanced calculations such as the law of the inverse square, which indicates that the intensity is inversely proportional to the square of the distance, which is decir, while the brightness of the star is found further.

Units of measurement such as the meter and the kilometer are very small in astronomy. Therefore, other distance units are used, such as light years and astronomical units, better known as AU, which are the most common units present in astronomical calculations that represent the average distance between the Earth and the Sun. and the parsec that is related distance measurements made in arcseconds.

One parsec is the distance that a star would be if the angle that forms with an astronomical unit of an arcsecond, on the other hand, an arcsecond and a degree divided between 3,600, therefore, a parsec equals 3.26 light-years.

Looking at the universe from a distance is looking at the past, distant objects allow us to understand that talking about the universe is practically talking about infinity. But there is still a data that serves as a reference to know the distances at which the distant stars are, for that it is necessary to know how far the Sun is from the Earth. How is it possible to measure the distance from the Sun to the Earth?

To answer this question, it is necessary to know that the first star from which the distance was calculated was the second century BC Moon. Eratosthenes had already calculated approximately the Earth's diameter, just after Hipparchus of Nicaea observed a lunar eclipse and saw how long it took the Moon to cross the Earth's shadow, he calculated that the Earth was three and a half times larger than the Moon. Thanks to Eratosthenes, the closest measurement to Earth was already known, about 12,700 kilometers, according to the metric system, which facilitated the calculation of the Moon's diameter, giving an approximate total of 3628 kilometers.

Another of Hipparchus' most relevant studies was that he held a coin in front of him, until the coin was the same size as the Moon, he measured the coin, then measured the distance between the coin and his eye and determined that the distance was 108 times the diameter of the coin. Therefore, the distance to the Moon must be the same ratio, 108 times the diameter of the Moon, resulting in 391,878 kilometers, very close to the current measurements of 384,400 kilometers.

Therefore, the way measurements are made in the universe is the same way Hipparchus used to know distances, the parallax, which is occupied by the nearest stars.

The difference is that they used stadiums as a unit of measure. This may explain the variation that exists between the distance I calculate to the Moon and the current record.

Returning to the previous question, who made the first calculation of the distance, from Earth to Sun, was Aristarchus of Samos, he deduced that when exactly half of the Moon was seen from his city, it meant that an imaginary line connecting the Earth with the Moon had to be at a right angle to the line from Moon to Sun. However, he did not perform the measurements well and assumed that the angle was 87°, so his calculation was wrong to determine the distance between the Earth and Sun, resulting in a distance 20 times greater than the distance between the Earth and the Moon. However, for a long time, no one was able to improve this calculation, today it is known that the distance is not 20 times, but 400 times the distance distance from Earth to Moon.

In this session, you learned how the universe is measured in addition to measurement units. The universe is infinitely big, it's wonderful to discover what it contains. Next time you have the opportunity to look at the stars, you'll remember that to know how far each one is, you had to know how far there is from the Sun to Earth.

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