Lab 7 – The HR Diagram

Ratio of Flux (brightness) between each magnitude step is 2.512 Magnitude Scale 2.512 2.512 2.512 x 2.512 x 2.512  16 2.512 1 2 3 4 5 6 Dimmer Brighter 2.512 2.512 Brightest stars in the night sky 2.512 x 2.512 x 2.512 x 2.512 X 2.512 = 100 Faintest stars visible to naked-eye 2.512 x 2.512  6.3 Ratio of Flux (brightness) between each magnitude step is 2.512

Absolute Magnitude C Apparent Magnitude B D A Sun 5 pc 10 pc 15 pc 4.2 5.0 6.0 0.0 B 3.3 2.0 D A 2.0 1.3 Sun -26.5 5 pc 10 pc 15 pc

Magnitude Stellar Brightness Apparent Magnitude (mv) - Brightness as seen from the Earth (Depends on the star's luminosity (wattage) and distance). Absolute Magnitude (Mv) - Brightness as seen from 10 pc (Depends only on the star's luminosity).

O B A F G K M -10 -5 +5 +10 +15 H-R Diagram The Sun +5 +10 +15 Absolute Magnitude Temperature H-R Diagram The Sun M=+5 G2

Stefan-Boltzmann Law E = T4 The Sun E A Hot Star E R R Rsun = Rhot star 6,000 K Temperature 12,000 K ? 1 L 16 L Stefan-Boltzmann Law E = T4 Luminosity

E E Surface Area = 4r2 6,000 K M1 = 5 M2 = 2 1 L 4 L Star 1 E Star 2 R1 R2 Surface Area = 4r2 6,000 K M1 = 5 M2 = 2 Star 2 is more luminous than Star 1: Star 2 is more luminous than Star 1: Mv1 - Mv2 = 5 - 2 = 3 magnitudes Star 2 is 16 time brighter because it has 16 times the surface area. Star 2 is more luminous than Star 1: Mv1 - Mv2 = 5 - 2 = 3 magnitudes Star 2 is 16 time brighter because it has 16 times the surface area M1 – M2 = 5 - 2 = 3 magnitudes Star 2 is 16 times brighter. Why? Star 2 has 16 times the surface area! 1 L 4 L

The Sun’s Spectral and Luminosity Class: G2 V Size Ia & Ib Supergiant II Bright Giant III Giant IV Sub-giant V Dwarf The Sun’s Spectral and Luminosity Class: G2 V

Stellar Luminosity Total amount of radiative energy emitted each second Surface Area (size of the star) Temperature (Stefan-Boltzmann Law)

The End.