The closest star to us is, of course, the Sun. The distance from the Earth to it is quite small in cosmic parameters: from the Sun to the Earth sunlight It only takes 8 minutes.

The Sun is not an ordinary yellow dwarf, as previously thought. This is the central body of the solar system, around which the planets revolve, with a large number of heavy elements. This is a star formed after several supernova explosions, around which a planetary system was formed. Due to its location close to ideal conditions, life arose on the third planet Earth. The Sun is already five billion years old. But let's figure out why it shines? What is the structure of the Sun and what are its characteristics? What does the future hold for him? How significant an impact does it have on the Earth and its inhabitants? The Sun is a star around which all 9 planets of the solar system, including ours, revolve. 1 a.u. (astronomical unit) = 150 million km - the same is the average distance from the Earth to the Sun. The Solar System includes nine large planets, about a hundred satellites, many comets, tens of thousands of asteroids (minor planets), meteoroids, and interplanetary gas and dust. At the center of it all is our Sun.

The sun has been shining for millions of years, which is confirmed by modern biological research obtained from the remains of blue-green-blue algae. If the temperature of the surface of the Sun changed by even 10%, all life on Earth would die. Therefore, it is good that our star evenly radiates the energy necessary for the prosperity of humanity and other creatures on Earth. In the religions and myths of the peoples of the world, the Sun has always occupied the main place. For almost all peoples of antiquity, the Sun was the most important deity: Helios - among the ancient Greeks, Ra - the sun god of the ancient Egyptians and Yarilo among the Slavs. The sun brought warmth, harvest, everyone revered it, because without it there would be no life on Earth. The size of the Sun is impressive. For example, the mass of the Sun is 330,000 times the mass of the Earth, and its radius is 109 times greater. But the density of our star is small - 1.4 times greater than the density of water. The movement of spots on the surface was noticed by Galileo Galilei himself, thus proving that the Sun does not stand still, but rotates.

Convective zone of the Sun

The radioactive zone is about 2/3 of the internal diameter of the Sun, and the radius is about 140 thousand km. Moving away from the center, photons lose their energy under the influence of collision. This phenomenon is called the phenomenon of convection. This is reminiscent of the process that occurs in a boiling kettle: energy coming from heating element, much Furthermore the amount of heat removed by conduction. Hot water, located close to the fire, rises, and the colder one goes down. This process is called convention. The meaning of convection is that denser gas is distributed over the surface, cools and again goes to the center. The mixing process in the convective zone of the Sun is carried out continuously. Looking through a telescope at the surface of the Sun, you can see its granular structure - granulations. It feels like it's made of granules! This is due to convection occurring beneath the photosphere.

Photosphere of the Sun

A thin layer (400 km) - the photosphere of the Sun, is located directly behind the convective zone and represents the “real solar surface” visible from Earth. Granules in the photosphere were first photographed by the Frenchman Janssen in 1885. The average granule has a size of 1000 km, moves at a speed of 1 km/sec and exists for approximately 15 minutes. Dark formations in the photosphere can be observed in the equatorial part, and then they shift. Strong magnetic fields are a distinctive feature of such spots. And the dark color is obtained due to the lower temperature relative to the surrounding photosphere.

Chromosphere of the Sun

Chromosphere of the Sun ( colored sphere) is a dense layer (10,000 km) of the solar atmosphere, which is located directly behind the photosphere. The chromosphere is quite problematic to observe due to its close location to the photosphere. It is best seen when the Moon covers the photosphere, i.e. during solar eclipses.

Solar prominences are huge emissions of hydrogen, resembling long luminous filaments. The prominences rise to enormous distances, reaching the diameter of the Sun (1.4 mm km), move at a speed of about 300 km/sec, and the temperature reaches 10,000 degrees.

The solar corona is the outer and extended layers of the Sun's atmosphere, originating above the chromosphere. The length of the solar corona is very long and reaches values ​​of several solar diameters. Scientists have not yet received a clear answer to the question of where exactly it ends.

The composition of the solar corona is a rarefied, highly ionized plasma. It contains heavy ions, electrons with a helium core, and protons. The temperature of the corona reaches from 1 to 2 million degrees K, relative to the surface of the Sun.

The solar wind is a continuous outflow of matter (plasma) from the outer shell of the solar atmosphere. It consists of protons, atomic nuclei and electrons. The speed of the solar wind can vary from 300 km/sec to 1500 km/sec, in accordance with the processes occurring on the Sun. The solar wind spreads throughout solar system and, interacting with magnetic field The Earth causes various phenomena, one of which is the northern lights.

Characteristics of the Sun

Mass of the Sun: 2∙1030 kg (332,946 Earth masses)
Diameter: 1,392,000 km
Radius: 696,000 km
Average density: 1,400 kg/m3
Axis tilt: 7.25° (relative to the ecliptic plane)
Surface temperature: 5,780 K
Temperature at the center of the Sun: 15 million degrees
Spectral class: G2 V
Average distance from Earth: 150 million km
Age: 5 billion years
Rotation period: 25.380 days
Luminosity: 3.86∙1026 W
Apparent magnitude: 26.75m

The characteristics of celestial bodies can be very confusing. Only stars have apparent, absolute magnitude, luminosity and other parameters. We will try to figure it out with the latter. What is the luminosity of stars? Does it have anything to do with their visibility in the night sky? What is the luminosity of the Sun?

Nature of stars

Stars are very massive cosmic bodies that emit light. They are formed from gases and dust as a result of gravitational compression. Inside stars there is a dense core in which nuclear reactions occur. They contribute to the glow of stars. The main characteristics of luminaries are spectrum, size, brilliance, luminosity, and internal structure. All these parameters depend on the mass of a particular star and its chemical composition.

The main “designers” of these celestial bodies are helium and hydrogen. In smaller quantities relative to them, they may contain carbon, oxygen and metals (manganese, silicon, iron). Young stars have the largest amounts of hydrogen and helium; over time, their proportions decrease, giving way to other elements.

In the inner regions of the star, the situation is very “hot”. The temperature in them reaches several million Kelvin. Here there are continuous reactions in which hydrogen is converted into helium. On the surface the temperature is much lower and reaches only a few thousand Kelvin.

What is the luminosity of stars?

Thermonuclear reactions inside stars are accompanied by energy releases. Luminosity is a physical quantity that reflects exactly how much energy a celestial body produces in a certain time.

It is often confused with other parameters, such as the brightness of stars in the night sky. However, brightness or visible value is an approximate characteristic that is not measured in any way. It is largely related to the distance of the star from the Earth and describes only how well the star is visible in the sky. The smaller the number of this value, the greater its apparent brightness.

In contrast, the luminosity of stars is an objective parameter. It does not depend on where the observer is. This is a characteristic of a star that determines its energetic power. It can change during different periods of the evolution of a celestial body.

Approximate to luminosity, but not identical, is absolute. It denotes the brightness of a star visible to an observer at a distance of 10 parsecs or 32.62 light years. It is commonly used to calculate the luminosity of stars.

Determination of luminosity

The amount of energy a celestial body emits is measured in watts (W), joules per second (J/s), or ergs per second (erg/s). There are several ways to find the required parameter.

It can be easily calculated using the formula L = 0.4(Ma -M), if you know the absolute magnitude of the desired star. Thus, the Latin letter L denotes luminosity, the letter M is the absolute magnitude, and Ma is the absolute magnitude of the Sun (4.83 Ma).

Another method involves greater knowledge about the luminary. If we know the radius (R) and temperature (T ef) of its surface, then the luminosity can be determined by the formula L=4pR 2 sT 4 ef. Latin s in this case means a stable physical quantity - the Stefan-Boltzmann constant.

The luminosity of our Sun is 3.839 x 10 26 Watts. For simplicity and clarity, scientists usually compare luminosity cosmic body exactly with this value. Thus, there are objects thousands or millions of times weaker or more powerful than the Sun.

Star luminosity classes

To compare stars with each other, astrophysicists use various classifications. They are divided by spectra, sizes, temperatures, etc. But more often than not, several characteristics are used at once for a more complete picture.

There is a central Harvard classification based on the spectra that the luminaries emit. It uses Latin letters, each of which corresponds to a specific color of radiation (O - blue, B - white-blue, A - white, etc.).

Stars of the same spectrum can have different luminosities. Therefore, scientists have developed the Yerke classification, which takes this parameter into account. It separates them by luminosity based on absolute magnitude. In this case, each type of star is assigned not only the letters of the spectrum, but also numbers responsible for luminosity. So, they distinguish:

• hypergiants (0);
• brightest supergiants (Ia+);
• bright supergiants (Ia);
• normal supergiants (Ib);
• bright giants (II);
• normal giants (III);
• subgiants (IV);
• main sequence dwarfs (V);
• subdwarfs (VI);
• white dwarfs (VII);

The higher the luminosity, the lower the absolute magnitude. For giants and supergiants it is indicated with a minus sign.

The relationship between the absolute magnitude, temperature, spectrum, and luminosity of stars is shown by the Hertzsprung-Russell diagram. It was adopted back in 1910. The diagram combines the Harvard and Yerke classifications and allows us to view and classify the luminaries more holistically.

Luminosity difference

The parameters of stars are strongly interrelated with each other. The luminosity is influenced by the temperature of the star and its mass. And they largely depend on the chemical composition of the star. The mass of a star becomes greater, the less heavy elements it contains (heavier than hydrogen and helium).

Hypergiants and various supergiants have the largest mass. They are the most powerful and brightest stars in the Universe, but at the same time, they are also the rarest. Dwarfs, on the contrary, have low mass and luminosity, but make up about 90% of all stars.

The most massive star currently known is the blue hypergiant R136a1. Its luminosity exceeds that of the sun by 8.7 million times. The variable star in the constellation Cygnus (P Cygnus) exceeds the luminosity of the Sun by 630,000 times, and S Doradus exceeds this parameter by 500,000 times. One of the smallest known stars, 2MASS J0523-1403, has a luminosity of 0.00126 solar.

Visually, the stars look different to an observer on earth: some shine brighter, others dimmer.

However, this does not yet indicate the true power of their radiation, since the stars are at different distances.

For example, the blue Rigel from the constellation Orion has a visible magnitude of 0.11, and the brightest Sirius, located nearby in the sky, has a visible magnitude of minus 1.5.

However, Rigel emits 2,200 times more visible energy than Sirius, and appears fainter only because it is 90 times farther away from us than Sirius.

Thus, the apparent magnitude itself cannot be a characteristic of the star, since it depends on the distance.

The true characteristic of a star’s radiation power is its luminosity, i.e., the total energy that the star emits per unit time.

Luminosity in astronomy, the total energy emitted by an astronomical object (planet, star, galaxy, etc.) per unit time. Measured in absolute units: watts (W) - in International system SI units; erg/s – in the GHS system (centimeter-gram-second); or in units of solar luminosity (solar luminosity L s = 3.86·10 33 erg/s or 3.8·10 26 W).

Luminosity does not depend on the distance to the object; only the apparent magnitude depends on it.

Luminosity is one of the most important stellar characteristics, allowing comparison between Various types stars on the diagrams “spectrum - luminosity”, “mass - luminosity”.

where R is the radius of the star, T is the temperature of its surface, σ is the Stefan-Boltzmann constant.

The luminosities of stars, it should be noted, are very different: there are stars whose luminosity is 500,000 times greater than the Sun, and there are dwarf stars whose luminosity is approximately the same amount less.

The luminosity of a star can be measured in physical units (say, watts), but astronomers more often express star luminosities in units of solar luminosity.

You can also express the true luminosity of a star using absolute magnitude.

Let's imagine that we have placed all the stars side by side and are viewing them from the same distance. Then the apparent magnitude will no longer depend on distance and will be determined only by luminosity.

The standard distance is 10 ps (parsec).

The apparent magnitude (m) that a star would have at that distance is called absolute magnitude (M).

Thus, absolute magnitude is a quantitative characteristic of the luminosity of an object, equal to the magnitude that the object would have at a standard distance of 10 parsecs.

Since illumination is inversely proportional to the square of the distance, then

where E is the illumination created by a star that is r parsec distant from the Earth; E 0 - illumination from the same star from a standard distance r 0 (10 pc).

Using Pogson's formula, we get:

m – M = -2.5lg(E/E 0) = -2.5lg(r 0 /r) 2 = -5lgr 0 + 5lgr.

this implies

M = m + 5lgr 0 - 5lgr .

For r 0 = 10 pc

M = m + 5 - 5lgr. (1)

If in (1) r = r 0 = 10 pc, That M = m– by definition of absolute magnitude.

The difference between the visible (m) and absolute (M) magnitudes is called the distance module

m - M = 5 lgr - 5 .

While M depends only on the star's own luminosity, m also depends on the distance r (in ps) to it.

For example, let's calculate the absolute magnitude for one of the brightest and closest stars to us - Centauri.

Its apparent magnitude is -0.1, its distance is 1.33 ps. Substituting these values ​​into formula (1), we get: M = -0.1 + 5 - 5lg1.33 = 4.3.

That is, the absolute magnitude of a Centauri is close to the absolute magnitude of the Sun, equal to 4.8.

One should also take into account the absorption of star light by the interstellar medium. This absorption weakens the star's brightness and increases the apparent magnitude m.

In this case: m = M - 5 + 5lgr + A(r), where the term A(r) takes into account interstellar absorption.

Luminosity
Apparent and absolute magnitudes
Wikipedia