Absolute limit stellar magnitudes: description, scale and brightness

If you raise your head upwards in a clear, cloudless night, you can see many stars. So much that, it seems, can not be counted at all. It turns out that the heavenly bodies, visible to the eye, are still counted. They number about 6 thousand. This is the total number for both the northern and southern hemispheres of our planet. Ideally, you and I, for example, in the northern hemisphere, should have seen about half of their total number, namely somewhere around 3 thousand stars.

The myriad of winter stars

Unfortunately, it is almost impossible to consider all the available stars, because for this you need conditions with a perfectly transparent atmosphere and complete absence of any light sources. Even if you find yourself in a clear field away from city illumination on a deep winter night. Why winter? Yes, because the summer nights are much lighter! This is due to the fact that the sun is not far behind the horizon. But even in this case, no more than 2.5-3 thousand stars will be available to our eye. Why is it so?

The thing is that the pupil of the human eye, if presented as an optical device, collects a certain amount of light from different sources. In our case, the sources of light are stars. How much we see them, directly depends on the diameter of the lens of the optical device. Naturally, the lens glass of a binocular or a telescope has a larger diameter than the pupil of the eye. Therefore, it will collect more light. Because of this, with the help of astronomical instruments you can see a much larger number of stars.

Starry sky with the eyes of Hipparchus

Of course, you noticed that the stars differ in brightness, or, as the astronomers say, by apparent brilliance. In the distant past, people also paid attention to this. Ancient Greek astronomer Hipparch divided all visible celestial bodies into stellar magnitudes having VI classes. The brightest of them "earned" I, and the most inexpressive, he described as stars of the VI category. The rest were divided into intermediate classes.

Later it became clear that different stellar magnitudes have some kind of algorithmic relationship. And the distortion of brightness in an equal number of times is perceived by our eye as the removal by the same distance. Thus, it became known that the radiance of a star of the 1st category is brighter than that of the sun II by approximately 2.5 times.

In the same time the star of class II is brighter than III, and the celestial star III, respectively, is IV. As a result, the difference between the luminescence of stars I and VI values is 100 times different. Thus, the heavenly bodies of the VII category are beyond the threshold of human sight. It is important to know that the star magnitude is not the size of the star, but its apparent brilliance.

What is the absolute stellar magnitude?

Star values are not only visible, but absolute. This term is used when it is necessary to compare two stars according to their luminosity. To do this, each star is referred to a conditionally standard distance of 10 parsecs. In other words, this is the magnitude of the stellar object that it would have if it was 10 PC away from the observer.

For example, the star magnitude of our sun is -26.7. But from a distance of 10 pc, our star would have been a barely perceptible eye of the object of the fifth magnitude. Hence follows: the higher the luminosity of the celestial object, or, as they say, the energy that the star radiates per unit time, the greater the probability that the absolute stellar magnitude of the object will take a negative value. And vice versa: the smaller the luminosity, the higher will be the positive values of the object.

The brightest stars

All stars have different visible luster. Some are slightly brighter than the first, while the latter are much weaker. In view of this, fractional quantities were introduced. For example, if the apparent stellar magnitude in its brilliance is somewhere between the I and II category, then it is considered to be a star of the 1.5 class. There are also stars with values of 2.3 ... 4.7 ... etc. For example, Procyon, which is part of the equatorial constellation of Small Dog, is best seen throughout Russia in January or February. Its apparent brilliance is 0.4.

It is noteworthy that I stellar magnitude is multiples of 0. Only one star almost exactly corresponds to it - this is Vega, the brightest star in the constellation of Lyra. Its brightness is about 0.03 magnitude. However, there are luminaries that are brighter than it, but their stellar magnitude is negative. For example, Sirius, which can be observed immediately in two hemispheres. Its luminosity is -1.5 magnitude.

Negative stellar magnitudes are assigned not only to stars, but to other celestial objects: the Sun, the Moon, some planets, comets and space stations. However, there are stars that can change their brilliance. Among them, there are a lot of stars pulsating, with varying amplitudes of brightness, but there are also some that can observe several pulsations simultaneously.

Measurement of stellar magnitudes

In astronomy, almost all distances measure the geometric scale of stellar magnitudes. The photometric method of measurement is used for distant distances, and also if it is necessary to compare the luminosity of an object with its apparent brilliance. In general, the distance to the nearest stars is determined from their annual parallax - the semimajor axis of the ellipse. Launched in the future, space satellites will increase the visual accuracy of the images by at least several times. Unfortunately, while for distances of more than 50-100 PC other methods are used.

Excursion to the open space

In the distant past, all the celestial bodies and planets were much smaller. For example, our Earth was once the size of Venus, and even in an earlier period - with Mars. Billions of years ago, all continents sheltered our planet with a continental continental crust. Later, the size of the Earth increased, and the continental plates dispersed, forming oceans.

All stars with the arrival of the "galactic winter" were growing temperature, luminosity and stellar magnitude. The measure of the mass of the heavenly body (for example, the Sun) increases with time. However, this was extremely uneven.

Initially, this small star, like any other giant planet, covered the solid ice. Later, the luminary began to increase in size until it reached its critical mass and did not stop growing. This is due to the fact that the stars periodically increase in their mass after the coming of the next galactic winter, and in inter-seasonal periods they are reduced.

Together with the Sun, the entire solar system grew. Unfortunately, not all the stars can go that route. Many of them disappear in the depths of other, more massive stars. The celestial bodies travel through the galactic orbits and, gradually approaching the very center, crumble to one of the nearest stars.

The galaxy is a super- gigantic star-planetary system that originated from a dwarf galaxy that emerged from a smaller cluster that emerged from a multiple planetary system. The latter came from the same system as ours.

Limit value of stars

Now it is no longer a mystery that the more transparent and darker the sky above us, the more stars or meteors you can see. Limit stellar magnitude is a characteristic that is better defined due to not only the transparency of the sky, but also to the vision of the beholder. A person can see the radiance of the faintest star only on the horizon, with a lateral vision. However, it is worth mentioning that this is an individual criterion for everyone. Compared to visual observation from a telescope, the essential difference is in the type of instrument and the diameter of its lens.

The permeability force of a telescope with a photographic plate fixes the emission of dim stars. In modern telescopes you can observe objects with a luminosity of 26-29 stellar magnitudes. The permeatory force of the device depends on a number of additional criteria. Among them, the quality of images is of no small importance.

The size of the star image directly depends on the state of the atmosphere, the focal length of the lens, the photographic emulsion, and the time allotted to the exposure. However, the most important indicator is the brightness of the star.