How do you define the brightness of a star in astronomy, or how do you visually distinguish its magnitude? Thanks

As early as more than 2,000 years ago, people began to divide the stars seen with the naked eye into six levels according to their brightness, and called this brightness level unique to astronomy magnitude. Very bright stars It is a 1st magnitude star, and a 6th magnitude star is just visible to the naked eye. Modern astronomy has continued this tradition and clearly stipulated that for every 1 magnitude difference, the brightness will differ by about 2.5 times. It is also stipulated that stars brighter than 1st magnitude stars are 0th magnitude stars, and brighter stars are represented by negative numbers.

With "zero magnitude" being the brightest, and "sixth magnitude" being the darkest, we can see it with the naked eye;

More are "seventh magnitude" and above star. It is now stipulated that for every 1 magnitude difference in a star, the brightness difference is 2.512 times. In this way, the brightness of a 1st magnitude star is exactly 100 times that of a 6th magnitude star. Sun -26.8, Moon -12.7, Saturn -0.4.

In fact, if you look at the starry night sky with the naked eye, the brightest stars you will find are 0-magnitude stars.

In order to measure the brightness of stars, astronomers created the concept of magnitude. The smaller the magnitude value, the brighter the star; the larger the magnitude value, the dimmer the star. The first person to classify the brightness of stars was the ancient Greek astronomer Hipparchus who lived in the 2nd century BC. He once compiled a catalog of stars. In the star catalog, he defined the 20 brightest stars as first-magnitude stars, and the stars just visible to the naked eye as sixth-magnitude stars. Then he divided four levels between first-magnitude stars and sixth-magnitude stars. This classification method is still used today. In 1850, the British astronomer Pousin proposed a unit for measuring the brightness of celestial bodies. A magnitude is defined as 2.512 times the brightness ratio. For example, a 5th magnitude star is 2.512 times brighter than a 6th magnitude star. Therefore, a magnitude difference of 5 magnitudes means a difference of 100 times in brightness. , because the magnitude range is too small, negative magnitude was introduced to measure extremely bright celestial objects. The apparent magnitude is the brightness of the celestial body seen by observers on the earth. The apparent magnitude of the sun is -26.7, and the full moon is about It is magnitude -11, and Sirius is magnitude -1.5. The absolute magnitude is the brightness seen at a distance of 10 parsecs (32.6 light years) from the celestial body. The absolute magnitude of the sun is 4.8 magnitude; the thermal magnitude is a measurement of the entire radiation of the star. Instead of measuring only a part of the visible light, the monochromatic magnitude is the magnitude obtained by measuring only a very narrow range of radiation in the electromagnetic spectrum; the narrow-band magnitude is the magnitude obtained by measuring a slightly wider frequency band. ; The measuring range of broadband magnitude is wider; the human eye is most sensitive to yellow, so visual magnitude can also be called yellow magnitude. Magnitude is an astronomical way of expressing the brightness of stars, recorded as m. Astronomy stipulates that the brightness of a star is expressed by magnitude. The smaller the magnitude number, the brighter the star. Every time the magnitude number differs by 1, the brightness of the star differs by approximately 2.5 times. The faintest stars we can see with the naked eye are 6th magnitude stars (6 m). The brightness in the sky is above magnitude 6 (that is, the magnitude is less than 6), which means we can see more than 6,000 stars. Of course, we can only see half of them every night, more than 3,000. When the moon is full, the brightness of the moon is equivalent to magnitude -12.6 (written as -12.6m in astronomy); the sun is the brightest celestial body we see, its brightness is -26.7m; and the largest astronomical telescope in the world today can see An object as dark as 24m. The "magnitude" we are talking about here actually reflects the brightness and darkness of celestial objects "as seen" from the earth, which is called "visual magnitude" in astronomy. The sun looks brighter than all the stars, and its apparent magnitude is much smaller than all the stars. This is just due to the light from its proximity to the earth. What's more, like the moon, it doesn't emit light at all, but only reflects some of the sun's light, making it the second brightest celestial body in people's eyes. There is also a concept of "absolute magnitude" in astronomy. This value can truly reflect the actual luminous ability of stars. The star equivalent obtained directly from the photometric measurement of a celestial body is related to the distance of the celestial body and is called the apparent magnitude, which reflects the apparent brightness of the celestial body. A very bright star can appear very dim because it is far away; and a star that is actually very dark can appear very bright because it is close. What is mentioned above is the apparent brightness of stars, that is, the apparent brightness. Visual brightness is expressed in terms of magnitude. The brightest stars we see are generally classified as 1st magnitude stars, and the dimmest stars that people with normal vision can barely see with the naked eye are classified as 6th magnitude stars. The bright star in the sky may really be a star with strong luminous ability, or it may only appear bright because it is very close to us. On the contrary, some dark stars are not necessarily really dark. Although they can only be observed through a telescope, their luminous ability may be extremely strong, but they appear dim because they are too far away from us. In order to compare the true luminous power of different stars, they should be compared at the same distance from us, just like a race must be on the same starting line. This "starting line" for stars is set at 10 parsecs, or 32.62 light years. The brightness of a star at this standard distance is specified as its absolute brightness, expressed in absolute magnitude. The absolute magnitude of a star is calculated. The apparent brightness of the Sun is unparalleled, but if you place it at 10 parsecs, which is 2.06 million times farther away than it is now, its absolute magnitude is only +4.8, making it a very dim star.

List of the fifty brightest stars: Sun -26.72 1 Sirius -1.46 8.6 2 Canopus -0.72 80 3 Rigel Kentaurus -0.30 4.3 4 Arcturus -0.04 30 5 Weaver actress Vega Tianqinzo 0.03 25 6 Five Capella Royal Poster 0.08 40 7 Rigel Orion 0.12 700 8 Nanhe PROCYON Picks 0.38 11 9 Victory Four Betelgeuse Orion 0.50 500 10 water committee 1 Hadar Centaur 0.61 330 12 Altair Aquila 0.77 16 13 Acrux Southern Cross 0.80 450 14 Aldebaran Taurus 0.85 60 15 Spica Virgo 0.97 350 16 Antares Scorpio 0.96 50 0 17 Pollux Gemini 1.14 35 18 Fomalhaut Fish 1.16 22 19 Deneb Cygnus 1.25 1800 20 Mimosa Southern Cross 1.25 500 21 Regulus Leo 1.35 70 22 Adhara Canis Major 1.50 600 23 Castor Gemini 1.58 50 24 Gacrux 1.63 80 25 Shaula 1.63 300 26 Bellatrix 1.64 400 27 Elnath Taurus 1.65 130 28 Miapla cidus Carina 1.68 50 29 Alnilam Orion 1.70 1300 30 Al Nair Crane 1.74 70 31 Alioth Ursa Major 1.77 60 32 Dubhe Ursa Major 1.79 70 33 Mirfak Perseus 1.80 500 34 Regor Sail 1.82 1000 35 Kaus Australis 1.85 120 36 Wezen 1.86 2800 37 Avior Carina 1.86 80 38 Alkaid 1.86 150 39 Sargas 1.87 200 40 Capella Menkalinan Auriga 1.90 60 41 Atria Triangulum 1.92 100 42 Alhena Gemini 1.93 80 43 Peacock 1.94 300 44 Mirzam Canis Major 1.98 700 45 Alphard 1.98 Hydra 110 46 Hamal Aries 2.00 70 47 Polaris Ursa Minor 2.02 400 48 Nunki Sagittarius 2.02 200 49 Diphda Cetus 2.04 60 50 Alnitak Orion