PHYSICS S5 Unit 14: Stellar Distance and Radiation.

What Will You Learn?

• The course Unit 14: Stellar Distance and Radiation will teach you the core methods and physical laws that astrophysicists use to measure the vast distances to stars and analyze the light they emit to determine their fundamental properties, such as temperature, size, and composition.
• I. Measuring Stellar Distance
• You will learn the techniques used to determine the scale of the Universe:
• • Parallax: You will study the trigonometric parallax method, the most direct technique for measuring nearby stars. This involves measuring the apparent shift in a star's position as the Earth orbits the Sun and using trigonometry to calculate the distance (d) in parsecs (pc).
• • Standard Candles (Conceptual): You will be introduced to the concept of objects with a known intrinsic brightness (luminosity), called Standard Candles (e.g., Cepheid variables), used to find distances to galaxies far beyond the reach of parallax.
• • Inverse Square Law: You will apply the principle that a star's apparent brightness decreases with the square of its distance, allowing distance to be calculated once its intrinsic luminosity is known: B α 1/d2.
• II. Stellar Radiation and Properties
• This section focuses on analyzing the light stars emit, treating them as massive blackbody radiators:
• • Wien's Displacement Law: This law relates a star's surface temperature (T) to the wavelength at which it emits the maximum amount of radiation (λmax):
• λmax α 1/T
• This is key to determining a star's color and temperature (e.g., blue stars are hotter than red stars).
• • Stefan-Boltzmann Law: This law relates a star's total luminosity (L) to its temperature (T) and its radius (R):
• L = 4πR2σT4
• By measuring L and T, this law allows for the calculation of the star's physical size.
• • Spectroscopy: You will learn how analyzing the absorption and emission lines in a star's spectrum reveals its chemical composition and, via the Doppler shift, its radial velocity (motion toward or away from us).
• III. Stellar Classification and Evolution
• The unit culminates in organizing and interpreting this vast amount of data:
• • Hertzsprung-Russell (H-R) Diagram: You will study the H-R Diagram
• , the primary tool for classifying stars, which plots luminosity against surface temperature.
• • Key Stellar Groups: You'll identify the main groups on the diagram: the Main Sequence (where most stars spend their lives), Giants, Supergiants, and White Dwarfs.
• • Stellar Evolution: Understanding a star's position on the H-R Diagram is crucial for inferring its age and predicting its future evolutionary path.