# 絕對星等

## 恆星與星系的絕對星等M

 星名 参宿四 参宿七 天津四 天狼星 太阳 绝对星等 -5.3 -6.7 -7.2 1.4 4.83 视星等 0.45 0.18 1.25 -1.46 −26.8

### 换算

${\displaystyle M=m+5\log _{10}{\frac {d_{0}}{d}}\!\,}$

${\displaystyle M=m+5(1+\log _{10}{\pi })\!\,}$

${\displaystyle m=M-5\log _{10}{\frac {d_{0}}{d}}\!\,}$

${\displaystyle m=M-5(1+\log _{10}{\pi })\!\,}$

#### 例子

M参宿七 = 0.18 + 5*log10(32.616/773) = -6.7

M织女星 = 0.03 + 5*(1 + log10(0.133)) = +0.65

m南门二 = 4.37 - 5*(1 + log10(0.750)) = -0.01

### 全波段星等

${\displaystyle M_{\mathrm {bol,\star } }-M_{\mathrm {bol,\odot } }=-2.5\log _{10}\left({\frac {L_{\star }}{L_{\odot }}}\right)}$

${\displaystyle {\frac {L_{\star }}{L_{\odot }}}=10^{0.4\left(M_{\mathrm {bol,\odot } }-M_{\mathrm {bol,\star } }\right)}}$

L是太陽的光度（全波段光度）
L是恆星的光度（全波段光度）
Mbol,⊙是太陽的全波段星等
Mbol,★是恆星的全波段星等。

## 太陽系天體的绝对星等H

### 计算

${\displaystyle H=m_{Sun}-5\log _{10}{\frac {{\sqrt {a}}r}{d_{0}}}\!\,}$

### 例子

${\displaystyle a_{Moon}\!\,}$  = 0.12, ${\displaystyle r_{Moon}\!\,}$  = 3476/2 km = 1738 km
${\displaystyle H_{Moon}=m_{Sun}-5\log _{10}{\frac {{\sqrt {a_{Moon}}}r_{Moon}}{d_{0}}}=+0.25\!\,}$

## 註釋

1. ^ IAU XXIX General Assembly Draft Resolutions Announced. [2015-07-08]. （原始内容存档于2021-04-18）.
2. IAU Inter-Division A-G Working Group on Nominal Units for Stellar & Planetary Astronomy. IAU 2015 Resolution B2 on Recommended Zero Points for the Absolute and Apparent Bolometric Magnitude Scales (PDF). Resolutions adopted at the General Assemblies (International Astronomical Union). 13 August 2015 [2018-11-02]. Bibcode:2015arXiv151006262M. . （原始内容 (PDF)存档于2016-01-28）.