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--- courses:ast403:photometry-and-spectroscopy [2026/02/12 08:49] – shuvo
+++ courses:ast403:photometry-and-spectroscopy [2026/02/12 08:50] (current) – shuvo
@@ Line 7: / Line 7: @@
 **Surface Brightness and Isophotes:** The fundamental measurement in galaxy photometry is surface brightness ($I(\mathbf{x})$), defined as the amount of light per square arcsecond at a specific point in a galaxy's image. Mathematically, it is expressed as:
 $$I(\mathbf{x}) = \frac{L}{4\pi D^2}$$
-where $L$ is luminosity and $D$ is the physical diameter of a patch of the galaxy. Surface brightness is typically measured in $mag \ arcsec^{-2}$ or $L_\odot \text{ pc}^{-2}$. A crucial property of surface brightness is that it is independent of the observer's distance, except at very large cosmological distances where the expansion of the Universe causes it to dim. Contours of constant surface brightness are called isophotes.
+where $L$ is luminosity and $D$ is the physical diameter of a patch of the galaxy. Surface brightness is typically measured in $\rm mag \ arcsec^{-2}$ or $L_\odot \text{ pc}^{-2}$. A crucial property of surface brightness is that it is independent of the observer's distance, except at very large cosmological distances where the expansion of the Universe causes it to dim. Contours of constant surface brightness are called isophotes.
 **Structural Profiles**: Astronomers use mathematical models to describe how a galaxy's light is distributed: