9702 · 25.1
Standard candles
Welcome to the world of **standard candles**, your cosmic tool for measuring vast distances in space! In this lesson, we'll explore how astronomers use specific celestial objects with known intrinsic brightness to gauge how far away stars and galaxies truly are. Understanding **luminosity**, **flux**, and key radiation laws will unlock the secrets of the universe's immense scale. This pilot aligns with **Senpai Corner** A Level notes (2025–2027) for topic **25.1**.
Need to know
What you need to know
- Luminosity L is defined as the total power output of radiation emitted by a star.
- It is measured in Watts.
- The observed amount of intensity F is the observed amount of intensity, or the radiant power transmitted normally through a surface per unit of area, of radiation measured on defined as Earth.
- Light leaving a star can be assumed to be a uniformly spread out like a spherical shell.
- Hence, the inverse square law of flux can therefore be calculated using 𝐹 = 𝐿 4𝜋𝑑 2 Here L is the luminosity of the source (watts), d is the distance between the star and Earth (m).
Explanation
Standard candles
- Luminosity L is defined as the total power output of radiation emitted by a star.
- It is measured in Watts.
- The observed amount of intensity F is the observed amount of intensity, or the radiant power transmitted normally through a surface per unit of area, of radiation measured on defined as Earth.
- Light leaving a star can be assumed to be a uniformly spread out like a spherical shell.