First-class starStellar brightnessCategory.The brightness of a star is closely related to its temperature. With the naked eye, we can distinguish different brightness among stars. The ancient GreeksHipachasAccording to the different brightness levels, the starlight is divided into six grades, the first grade star is the brightest, and the sixth grade star is the darkest.The difference between the brightness of each order star is 2.512 times, and the difference between the actual brightness of the first order star and the sixth order star is 100 times.These six levels are calledApparent magnitudeThe apparent magnitude, regardless of the distance of the star, is the brightness we show when looking at the star on the earth.
Differences in the brightness of stars in the night sky
The apparent magnitude, regardless of the distance between stars, is the brightness we show when looking at stars on the earth.But in fact, some stars that look extremely bright may not be very luminous, just because they are very close to us.Similarly, some stars that look very dark may be very bright stars, just because they are far away from us.
People extend the brightness level division to the range of decimal and negative numbers.According to this classification, the brightness of the moon at full moon is - 12.6 stars, and the sun on sunny days is - 26.8 stars.Besides the sun, the brightest stars in the sky areSiriusIt is a star of - 1.6 magnitude.Compared with Sirius, the difference between the sun and Sirius is only 25.2the magnitudeBut in fact, the brightness difference between them is 12 billion times.The darkest star that astronomers can see with modern telescopes is a star of class 20. If you take photos, you can see a star of class 23.
Absolute magnitude
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32.62 Light year equidistant measurement
Absolute magnitudeIt measures the luminous ability of stars. Theoretically, such stars are ubiquitous and numerous, such asVegaThe absolute magnitude of is+0.65, soHerotuOn the same sequence as itMain sequence starAll the stars darker than it are first class stars.If the absolute magnitude is represented by M,Apparent magnitudeRepresented by m, the distance of a star becomesSecond gapIf the number is r, then M=m+5-5lgr.Therefore, given a star (measured apparent magnitude) and known distance, the absolute magnitude can be directly calculated.
Therefore, in order to compare the luminosity emitted by the stars themselves, astronomers assume that all the stars are placed at the same distance (32.6 light-years), so as to determine their luminosity and absolute magnitude.In terms of absolute magnitude, the sun is just a weak star visible to the naked eye, which belongs to 4.8 absolute magnitude.Sirius belongs to 1.3Absolute magnitude, so it is 25 times brighter than the sun.
Magnitude division
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There is a difference between light and dark stars.Obviously bright star ratioDark starMuch more.In order to show the brightness of stars, people use "magnitude" to grade the stars in the whole sky: the darkest star visible to the naked eye is 6, the star brighter than 6 is 5, the brightest is 4... the brightest is 1.
A star of magnitude 1 is about 2.5 times brighter than a star of magnitude 2 and 6.2 times brighter than a star of magnitude 3.
Altair is a first order star.VegaNiulang StarIt is still bright, set as 0, etc.Those brighter than stars of magnitude 0 are - 1, - 2, and so on. Sirius, the brightest star in the sky, has a magnitude of - 1.6.
On the other hand, the stars that are darker than the sixth class stars are the seventh, eighth and ninth class stars... They have to be observed with telescopes.TelescopicObjective apertureThe larger, the darker stars can be observed.The world's largest telescope can observeDark celestial body。
After measuring the magnitude of each star in the sky, you can count aMagnitude rangeInternalNumber of starsHas.For example, we classify stars of less than 1.5 degrees as "first-class stars", those of 1.6 to 2.4 degrees as "second-class stars", and those of 2.5 to 3.4 degrees as "third-order stars".
Generally speaking, the darkest star that can be seen by people with visual acuity of 1.5 is close to 6.5.This can only be achieved on a high mountain far from the city lights and with a completely dark sky.
According to legend, the ancient GreeksHipachasThe brightness of stars in the sky was first divided into six grades.The lightest one is level 1, the second lightest one is level 2, and the darkest one is level 6. This method is rough.Later, someone subdivided each magnitude into 10 or 100 degrees, so that the magnitude has a decimal. For example,the galaxy(Tianhe) East BankNiulang StarThe star magnitude of is 0.77, which is taken to one decimal place. According to the rounding rule, it is 0.8, and more simply, it is 1.
If a star is brighter than Altair, its magnitude is 0.0 originally means "no", but it means "yes" in star magnitude, that is, it is brighter than a star of magnitude 1.For example, on the west bank of the Milky WayVegaIs a star of magnitude 0.
There are many stars in the sky that are brighter than Vega. Astronomers came up with the idea of using a number preceded by a "-" sign (pronounced negative here).For example, the magnitude of Sirius is - 1.6.At night, except the moon, the brightest stars in the whole day can be seenVenusIts brightest star magnitude is - 4.5.The greater the negative number, the brighter the stars.According to this method, the magnitude of the full moon is - 16, and the magnitude of the sun is - 27.
The stars that are darker than the sixth order are in order of magnitude 7 and 8.Such stars can only be observed with telescopes.China's largestAstronomical telescope(diameter 2.16m, installed onXinglong Observatory of Beijing Astronomical Observatory）A star of 19 degrees can be observed.The world's largest telescope (with a diameter of 6 meters, installed on thecaucasus mountains Above), stars of 22 degrees can be observed.
