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Astronomy 105 Laboratory Lab 07.

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Presentation on theme: "Astronomy 105 Laboratory Lab 07."— Presentation transcript:

1 Astronomy 105 Laboratory Lab 07

2 Lab 07 The Hr diagram

3 Measuring a Star’s Brightness
Magnitude Scale (2.512)5 = 100 2.512 (2.512)2  6.3 Brighter Dimmer Brightest stars in the night sky (2.512)3  16 Faintest stars visible to naked-eye Difference in apparent brightness between each magnitude step is 2.512

4 1 parsec (pc) = 3.26 ly Absolute Magnitude C Apparent Magnitude B D A
1.2 1 parsec (pc) = 3.26 ly Absolute Magnitude 5.0 6.0 0.0 2.4 B 2.0 D A 2.0 4.0 Sun -26.5 5 pc 10 pc 15 pc

5 Absolute magnitude depends only on a star’s luminosity
Stellar Brightness Apparent Magnitude (mv) - Brightness from Earth Absolute Magnitude (Mv) - Brightness from 10 pc Absolute magnitude depends only on a star’s luminosity

6 Spectral Classification
B

7 Spectral Classification
(a temperature scale) O B A F G K M h e ine irl iss /Guy Hot 30,000 K A0 A1 A2 A3 A4 A5 A6 A7 A8 A9 F0 Sun (G2) 6,000 K Cool 3,500 K

8 Absolute Magnitude - Luminosity
Stellar Luminosity -- Total amount of light energy emitted each second Surface Area Temperature

9 Both stars same Temperature
Stellar Luminosity E E  T4 Both stars same Temperature 6,000 K 6,000 K 1 Lsun 1 Lsun

10 Stellar Luminosity  Temperature
E  T4 1 m2 1 m2 Both stars are the same size 6,000 K 12,000 K 1 Lsun 16 Lsun ?

11 Stellar Luminosity  Temperature
3 times hotter E  T4 Both stars are the same size 6,000 K 18,000 K 1 Lsun 81 Lsun ?

12 Stellar Luminosity  Size
E  R2 R Both stars same Temperature 6,000 K 1 Lsun 6,000 K ? 4 Lsun

13 Stellar Luminosity  Size
E  R2 R Both stars same Temperature 1 Lsun ? 9 Lsun

14 Stellar Luminosity – Total amount of light energy emitted each second
Surface Area Temperature E  R2T4

15 The H-R Diagram L = 1 Lsun G2 The Sun H-R Diagram 106 104 102 1 10-2
O B A F G K M 106 104 102 1 10-2 10-4 Luminosity Temperature H-R Diagram

16

17 The End

18 Stellar Luminosity  Size
same energy per m2 E  T4 R Both stars same Temperature Surface Area = 4r2 6,000 K 6,000 K 1 Lsun ? 1 Lsun 4 Lsun

19 Stellar Luminosity  Size
same energy per m2 E  T4 2R R Both stars same Temperature Surface Area = 4r2 6,000 K 6,000 K 1 Lsun ? 1 Lsun 4 Lsun

20 Stellar Luminosity  Size
same energy per m2 E  T4 2R R Both stars same Temperature Surface Area = 4r2 6,000 K 6,000 K 1 Lsun ? 1 Lsun 4 Lsun

21 Luminosity: Size E E 8,000 K Msmall = 5 Mbig = 2
Small Star Big Star Rs Rb Msmall = 5 8,000 K Mbig = 2 Big Star is more luminous than Small Star: Msmall – Mbig = = 3 magnitudes Star 2 is more luminous than Star 1: Mv1 - Mv2 = = 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 = = 3 magnitudes Star 2 is 16 time brighter because it has 16 times the surface area. Big Star is 16 times brighter. Why? Big Star has 16 times the surface area! Surface Area = 4r2

22

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

24 Luminosity: Temperature
The Sun E A Hot Star E R R Rsun = Rhot star 6,000 K Temperature 12,000 K 1 Lsun Luminosity 16 Lsun ?

25 HR Diagram

26 HR Diagram Vertical Axis: Absolute Magnitude or Luminosity Horizontal Axis: Temperature (color, Kelvin or spectral type) O B A F G K M -10 -5 +5 +10 +15 Absolute Magnitude Temperature The Sun M = +5 G2

27 The Sun’s Spectral and Luminosity Class: G2 V

28 Lab Quiz 7

29 Last week you determined the Earth’s orbital velocity using ______.
Newton’s 2nd Law Wein’s Law the photoelectric effect Newton’s Law of Gravity the Doppler effect 28

30 If a star is moving away from Earth, the absorption lines in its spectrum will
have wavelengths shorter than those of an identical stationary star (blueshifted). have wavelengths longer than those of an identical stationary star (redshifted). be the same as those of an identical stationary star. 28

31 In this week’s lab you will be using a graph (HR diagram) comparing two stellar properties. Which property is plotted on the horizontal axis? mass size temperature or spectral class luminosity or absolute magnitude eccentricity 28

32 A star’s apparent magnitude is a measure of brightness as viewed from
the Earth. 10 parsecs. 100 parsecs. 1000 parsecs. 10 light-years 20

33 A star’s absolute magnitude is a measure of brightness as viewed from
the Earth. 10 parsecs. 100 parsecs. 1000 parsecs. 10 light-years 25

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