Cosmology Revision Notes

These notes are to aid in the understanding of cosmology as part of the OCR A Level Physics syllabus.

Key Concepts and Units

• Astronomical Unit (AU): A standard unit of measurement in astronomy.
• Parsec (pc): Another unit of distance used in astronomy, equivalent to approximately 3.26 light-years.
• The relationship between these units often involves trigonometric calculations like tangent (tan).

Angular Measurements

• Arcsecond Conversion:
  • 1 degree = 3600 arcseconds
  • Trigonometric calculations often convert arcseconds into other units for parallax measurements.

Important Formulas

• Parallax Formula:
  • tan(θ) = opp / adj
  • Used to calculate distances in parsecs from observed parallax angles.
• Doppler Effect Formula (for light):
  • Δλ/λ = v/c where:
  • Δλ is the change in wavelength
  • λ is the original wavelength
  • v is the relative velocity between the source and observer
  • c is the speed of light. A positive Δλ indicates redshift (source moving away).

Example Calculations

• Distance Calculations:
  • Given example numbers such as 1.471 x 10^11 or 1.521 x 10^11 for specific calculations.
  • Conversion constants like 1.496 x 10^11 which may relate to AU measurements.

Velocity and Frequency

• Frequency (f) and Velocity (v):
  • Important for understanding wave-related phenomena in cosmology, specifically light and sound waves.
• Speed of Light (c):
  • Standard constant c = 3.00 x 10^8 m/s

Cosmological Constants

• Various constants are used throughout the notes, often denoted with powers of ten, such as 4.13 x 10^16 or 3.1 x 10^16.

Example Problems

• Example Values:
  • Numbers like 0.768 = 1.30 pc relate to specific problem solutions.
  • Used in calculations to find distances in the cosmos.

The Doppler Effect in Cosmology

• The Doppler effect explains the redshift observed in the light from distant galaxies. As galaxies move away from us, the wavelength of their light is stretched, causing a shift towards the red end of the spectrum. This redshift is used to measure the expansion rate of the universe.