If you raise your head up on a clear cloudless night, you can see a lot of stars. So many that it seems impossible to count at all. It turns out that the celestial bodies visible to the eye are still counted. There are about 6 thousand of them. This is the total number for both the northern and southern hemispheres of our planet. Ideally, you and I, being, for example, in the northern hemisphere, should have seen about half of their total number, namely, somewhere around 3 thousand stars.
Myriad winter stars
Unfortunately, it is almost impossible to consider all the available stars, because this will require conditions with a perfectly transparent atmosphere and the complete absence of any light sources. Even if you find yourself in an open field away from city light on a deep winter night. Why in winter? Yes, because summer nights are much brighter! This is due to the fact that the sun does not set far below the horizon. But even in this case, no more than 2.5–3 thousand stars will be available to our eye. Why is that?
The thing is that the pupilThe human eye, if we imagine it as an optical instrument, collects a certain amount of light from different sources. In our case, the light sources are stars. How many we will see them directly depends on the diameter of the lens of the optical device. Naturally, the lens glass of binoculars or a telescope has a larger diameter than the pupil of the eye. Therefore, it will collect more light. As a result, a much larger number of stars can be seen using astronomical instruments.
Starry sky through the eyes of Hipparchus
Of course, you have noticed that stars differ in brightness, or, as astronomers say, in apparent brilliance. In the distant past, people also paid attention to this. The ancient Greek astronomer Hipparchus divided all the visible celestial bodies into stellar magnitudes that have VI classes. The brightest of them "earned" I, and he described the most inexpressive ones as category VI stars. The rest were divided into intermediate classes.
Later it turned out that different stellar magnitudes have some kind of algorithmic connection between them. And the distortion of brightness in an equal number of times is perceived by our eye as a removal by the same distance. Thus, it became known that the radiance of a category I star is brighter than the radiance of II by about 2.5 times.
A star of class II is brighter than class III by the same number of times, and a celestial body of III, respectively, is brighter than IV. As a result, the difference between the glow of stars of I and VI magnitudes differs by 100 times. Thus, the celestial bodies of the VII category are beyond the threshold of human vision. It is important to know that the starmagnitude is not the size of a star, but its apparent brilliance.
What is absolute magnitude?
Star magnitudes are not only visible, but also absolute. This term is used when it is necessary to compare two stars with each other by their luminosity. To do this, each star is referred to a conventionally standard distance of 10 parsecs. In other words, this is the size of a stellar object that it would have if it was at a distance of 10 PCs from the observer.
For example, the magnitude of our sun is -26.7. But from a distance of 10 PCs, our star would be a barely visible object of the fifth magnitude. It follows from this: the higher the luminosity of a celestial object, or, as they say, the energy that a star radiates per unit time, the more likely it is that the absolute magnitude of the object will take a negative value. And vice versa: the lower the luminosity, the higher the positive values of the object will be.
The brightest stars
All stars have different apparent brilliance. Some are slightly brighter than the first magnitude, the latter are much weaker. In view of this, fractional values were introduced. For example, if the apparent stellar magnitude in its brilliance is somewhere between categories I and II, then it is considered to be a class 1, 5 star. There are also stars with magnitudes 2, 3…4, 7…etc. For example, Procyon, which is part of the equatorial constellation Canis Minor, is best seen throughout Russia in January or February. Her apparent brilliance is 0.4.
It is noteworthy that Imagnitude is a multiple of 0. Only one star almost exactly corresponds to it - this is Vega, the brightest star in the constellation Lyra. Its brightness is approximately 0.03 magnitude. However, there are luminaries that are brighter than it, but their magnitude is negative. For example, Sirius, which can be observed in two hemispheres at once. Its luminosity is -1.5 magnitude.
Negative stellar magnitudes are assigned not only to stars, but also to other celestial objects: the Sun, the Moon, some planets, comets and space stations. However, there are stars that can change their brightness. Among them there are many pulsating stars with variable brightness amplitudes, but there are also those in which several pulsations can be observed simultaneously.
Measurement of stellar magnitudes
In astronomy, almost all distances are measured by the geometric scale of stellar magnitudes. The photometric measurement method is used for long distances, and also if you need to compare the luminosity of an object with its apparent brightness. Basically, the distance to the nearest stars is determined by their annual parallax - the major semi-axis of the ellipse. Space satellites launched in the future will increase the visual accuracy of images by at least several times. Unfortunately, other methods are still used for distances greater than 50–100 PCs.
Excursion to outer space
In the distant past, all celestial bodies and planets were much smaller. For example, our Earth was once the size of Venus, and even earlier, the size of Mars. Billions of years ago, all the continents covered our planet with a continuous continental crust. Later, the size of the Earth increased, and the continental plates parted, forming oceans.
All stars with the advent of "galactic winter" increased temperature, luminosity and magnitude. The measure of the mass of a celestial body (for example, the Sun) also increases with time. However, this was extremely uneven.
Initially, this small star, like any other giant planet, was covered with solid ice. Later, the star began to increase in size until it reached its critical mass and stopped growing. This is due to the fact that the stars periodically increase in their mass after the next galactic winter, and decrease during the off-season periods.
The entire solar system grew along with the Sun. Unfortunately, not all stars will be able to follow this path. Many of them will disappear into the depths of other, more massive stars. Celestial bodies turn in galactic orbits and, gradually approaching the very center, collapse onto one of the nearest stars.
Galaxy is a supergiant star-planetary system that originated from a dwarf galaxy that originated from a smaller cluster that emerged from a multiple planetary system. The latter came from the same system as ours.
Limiting star size
Now it is no longer a secret that the more transparent and darker the sky above us, the more stars or meteors you can see. Limit starmagnitude is a characteristic that is better determined due not only to the transparency of the sky, but also to the vision of the beholder. A person can see the radiance of the dimmest star only on the horizon, with peripheral vision. However, it is worth mentioning that this is an individual criterion for each. When compared with visual observation from a telescope, the essential difference is the type of instrument and the diameter of its lens.
The penetration force of a telescope with a photographic plate captures the radiation of dim stars. Modern telescopes can observe objects with a luminosity of 26–29 magnitudes. The penetrating power of the device depends on many additional criteria. Among them, image quality is of no small importance.
The size of a star image directly depends on the state of the atmosphere, the focal length of the lens, emulsion, and the time allotted for exposure. However, the most important indicator is the brightness of the star.
