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15 - Patterns in the Stars

Important Concepts for This Unit

  1. Stars can be grouped based on properties such as temperature and luminosity
  2. The Main Sequence organizes stars by their properties.
  3. A star's position on the Main Sequence helps us determine many of its properties. The Main Sequence for astronomers is akin to the periodic table for chemists.

The HR Diagram – Study Guide

 Important topics are below. The test will be in 2 parts, 60 minutes total.

Part A of the test (conceptual, no HR Diagram provided)

Stellar Classification

  • The history behind the stellar spectral types (OBAFGKM)
  • The physics underlying the Stellar Spectral Types
  • Classify stars spectral class and luminosity class by examining/interpreting spectra

HR Diagram

  • Be able to draw it, with labeled axes, including spectral type, and Luminosity Classes.
  • Properties of stars on the Main Sequence vs. other areas of the HR Diagram.
  • Masses and lifetimes along Main Sequence
  • Luminosity and stellar radii relationships
  • Be able to place stars on the HR diagram based on various properties (spectral class, luminosity class, etc.)

Part B of the test (mathematical, HR Diagram provided), after Part-A is collected.


  • Compute a star’s luminosity and distance using spectrum, flux, and parallax information
  • Calculate stellar properties using HR Diagram and spectrum information
  • Compute stellar lifetimes using mass and luminosity values

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Read 15.1 and 15.2. Do problems 1, 2, 3, 4, 6, 7, 9, 10, 11, 12, 14, 49, 50 December 14, 2017  
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Near Star Luminosity.csv
Nikhil Joshi,
Nov 20, 2014, 1:21 PM
Nikhil Joshi,
Dec 4, 2017, 1:59 PM