Intrinsic brightness

The absolute magnitude is an auxiliary variable in astronomy, to compare the actual brightness, ie the luminosities of celestial objects can.

From Earth, we see a star with its apparent brightness as it is affected by its distance and interstellar matter.

For determining the absolute brightness using a uniform distance. This is 10 parsecs ( 32.6 light years) for stars and one astronomical unit ( AU) for ( reflective ) objects of the solar system. The relative brightness that would measure from this standard distance, an observer is called absolute brightness. In stars which are less than 10 Parsecs removed, the apparent brightness is greater than the absolute magnitude and vice versa. As with the apparent brightness, a smaller numerical value greater luminance.

Absolute magnitudes are as apparent brightnesses in magnitudes (mag ) specified. Especially in older works on astronomy one often finds the notation with a superscript M on the decimal point, for example, in a star of the third ( absolute ) size class. The use of the capital letter illustrates this is that it is an absolute brightness.

The brightest fixed stars reach absolute magnitudes of about -9 mag ( about 100,000 times the luminosity of the sun ), the faintest contrast 17 mag ( about one ten -thousandth of the solar luminosity).

Bolometric magnitude

This indicates the brightness of a star across the electromagnetic spectrum. The required correction depends on the sensitivity range of the instrument and of spectral type of the object in question. The photographic brightness of the sun is, the bolometric magnitude against it.

Distance modulus

The difference between apparent magnitude m and absolute magnitude M is called the distance modulus, because it is in a fixed relation to the distance. For the determination of levels of brightness follows:


Are you the Entfernungsmaßzahl as a dimensionless number, so it is

From the definition of parallax follows as the relationship between Entfernungsmaßzahl and annual parallax π ( as a dimensionless number in seconds of arc )

This then results in

With the help of this important for astronomy formula ( eg Cepheids or supernovae of type Ia ), the distance can be calculated for stars whose luminosity is known. In this way it was 1923, the distance of the Andromeda nebula can be determined.

Comparison Apparent / Absolute brightness of some stars in the visual

Objects in the solar system

When comets and asteroids, the term absolute magnitude is defined differently, as they only reflect light. Here the situation is assumed that the object ( comet or asteroid ) exactly one astronomical unit is removed from the sun and is observed from the Sun. The brightness of the object would be seen is referred to as absolute brightness.