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Most stars visible to the naked eye are within a few hundred parsecs of the Sun, with the most distant at a few thousand parsecs, and the Andromeda Galaxy at over 700,000 parsecs. [3] The word parsec is a shortened form of a distance corresponding to a parallax of one second, coined by the British astronomer Herbert Hall Turner in 1913. [4]
The apparent magnitude, the magnitude as seen by the observer (an instrument called a bolometer is used), can be measured and used with the absolute magnitude to calculate the distance d to the object in parsecs [14] as follows: = + or = (+) / where m is the apparent magnitude, and M the absolute magnitude. For this to be accurate, both ...
For objects within the immediate neighborhood of the Sun, the absolute magnitude M and apparent magnitude m from any distance d (in parsecs, with 1 pc = 3.2616 light-years) are related by = = (), where F is the radiant flux measured at distance d (in parsecs), F 10 the radiant flux measured at distance 10 pc.
Isolating from the equation =, finds that the distance (or, the luminosity distance) in parsecs is given by = + The uncertainty in the distance in parsecs ( δd ) can be computed from the uncertainty in the distance modulus ( δμ ) using δ d = 0.2 ln ( 10 ) 10 0.2 μ + 1 δ μ ≈ 0.461 d δ μ {\displaystyle \delta d=0.2\ln(10)10^{0. ...
Knowing the apparent magnitude (m) and absolute magnitude (M) of the star, one can calculate the distance (d, in parsecs) of the star using = (/) (see distance modulus). The true distance to the star may be different than the one calculated due to interstellar extinction. [3]
Absolute magnitude is defined as the apparent magnitude that a star or object would have if it were observed from a distance of 10 parsecs (33 light-years; 3.1 × 10 14 kilometres; 1.9 × 10 14 miles). Therefore, it is of greater use in stellar astrophysics since it refers to a property of a star regardless of how close it is to Earth.
Newcomb's value for the solar parallax (and for the constant of aberration and the Gaussian gravitational constant) were incorporated into the first international system of astronomical constants in 1896, [48] which remained in place for the calculation of ephemerides until 1964. [49]
This is known as the distance modulus, where d is the distance to the star measured in parsecs, m is the apparent magnitude, and M is the absolute magnitude. If the line of sight between the object and observer is affected by extinction due to absorption of light by interstellar dust particles , then the object's apparent magnitude will be ...