Radiation Pressure Calculator
Calculate electromagnetic radiation pressure from stellar sources and inside stars
Calculate Radiation Pressure
Opaque surfaces absorb photons, reflective surfaces reflect them
Total energy output of the star per second
Distance from the radiation source
Angle between light beam and surface normal (0° = perpendicular)
Outside Star Formula
x: surface factor, L: luminosity, α: angle,
R: distance, c: speed of light
Radiation Pressure Results
Pressure Analysis
Example: Solar Pressure on Earth
Given Data
Surface: Opaque (x = 1)
Solar luminosity: 1 L☉ = 3.828×10²⁶ W
Distance: 1 AU = 1.496×10¹¹ m
Angle: 0° (perpendicular)
Result
p = (1 × 3.828×10²⁶ × 1) / (4π × (1.496×10¹¹)² × 3×10⁸)
p = 4.54 μPa
Tiny but measurable for solar sails!
Example: Inside Sun's Corona
Given Data
Temperature: 5,000,000 K
Stefan-Boltzmann: σ = 5.67×10⁻⁸ W/(m²·K⁴)
Speed of light: c = 3×10⁸ m/s
Result
p = (4 × 5.67×10⁻⁸ × (5×10⁶)⁴) / (3 × 3×10⁸)
p = 157.6 GPa
10¹⁷ times greater than Earth!
Radiation Pressure Basics
Photon Momentum
Light carries momentum p = E/c
Energy-momentum relation for photons
Surface Interaction
Absorption vs reflection affects pressure
Reflective surfaces experience 2× pressure
Stellar Balance
Radiation pressure balances gravity in stars
Prevents stellar collapse
Applications
Solar Sails
Spacecraft propulsion using sunlight
Stellar Physics
Understanding star structure and evolution
Optical Tweezers
Manipulating microscopic particles
Astrophysics
Comet tails and dust grain dynamics
Physical Constants
Note: These constants ensure accurate calculations across astronomical scales
Understanding Radiation Pressure
What is Radiation Pressure?
Radiation pressure is the physical pressure exerted upon a surface due to the exchange of momentum between electromagnetic radiation and the surface. When photons (particles of light) hit a surface, they transfer their momentum, creating a small but measurable force.
Surface Types
- •Opaque surfaces: Absorb photons completely (x = 1)
- •Reflective surfaces: Reflect photons back (x = 2)
- •Real materials: Partially absorb and reflect (1 < x < 2)
Two Calculation Methods
Outside Star (Solar Pressure)
p = (x × L × cos²(α)) / (4π × R² × c)
Used for calculating pressure from distant sources like the Sun on planets, solar sails, or spacecraft.
Inside Star (Internal Pressure)
p = (4σT⁴) / (3c)
Used for calculating internal radiation pressure that balances gravitational collapse in stellar interiors.
Stellar Physics Significance
In stellar physics, radiation pressure plays a crucial role in preventing gravitational collapse. The hot interior of a star generates intense electromagnetic radiation that creates outward pressure, balancing the inward gravitational force.
For massive stars (> 20 solar masses), radiation pressure can dominate over gas pressure, affecting stellar structure and evolution. This is why very massive stars are unstable and have shorter lifespans than smaller stars like our Sun.