Chapter 16/Chapter17Chapter 16/Chapter17

Questions of the DayQuestions of the Day What are stars? What are their properties?What are stars? What are their properties?

Who was Annie Jump Cannon? Why was she Who was Annie Jump Cannon? Why was she important to the study of stars?important to the study of stars?

What is stellar spectroscopy? What does it tell us What is stellar spectroscopy? What does it tell us about a star?about a star?

What is the Sun? Why is it important to study this What is the Sun? Why is it important to study this particular star?particular star?

Parallax of a StarParallax of a Star

)(" Angle Parallax1(parsec) Distance

Parallax of a StarParallax of a Star

parsecs50.2"1Distance

Parallax1Distance

0.2"Parallax

Differential MagnitudeDifferential Magnitude

12

12

mm

2

1

5.2mm

2

1

12

2

1

12

1

2

121

2

5.2ff

10ff

5.2mm

fflog

5.2mm

fflog

mmfflog5.2

Differential MagnitudeDifferential Magnitude

Two stars have a magnitude of 7 and 3. How Two stars have a magnitude of 7 and 3. How much brighter is the star with a magnitude of 3 much brighter is the star with a magnitude of 3 than the star with a magnitude of 7?than the star with a magnitude of 7?

X40ff

5.2ff

5.2ff

7m3m

2

1

37

2

1

mm

2

1

2

1

12

Distance ModulusDistance Modulus

121

2

21

22

1

2

mmfflog5.2

)parsec10(4Lfd4

(L)Luminosityf

Mmmm

Distance Modulus Distance Modulus

m10dlog5M

Mm10dlog5

Mmd10log5

Mmd10log5.2

Mm)10(4

Ld4

Llog5.2

2

2

2

Distance ModulusDistance Modulus

A star has a absolute magnitude of -5 and a A star has a absolute magnitude of -5 and a distance of 1000 parsecs. What is the distance of 1000 parsecs. What is the magnitude of the star as view from Earth?magnitude of the star as view from Earth?

m5m105

m)100log(55

mpc10pc1000log55

mpc10dlog5M

pc1000d5M

Fig.16.09Fig.16.09

Annie Jump CannonAnnie Jump Cannon

1863 – 1941 A.D.1863 – 1941 A.D. Born in Delaware, Born in Delaware,

grew up in Dover, grew up in Dover, Delaware.Delaware.

Entered Wellsley Entered Wellsley CollegeCollege

http://astro.wsu.edu/worthey/astro/html/im-women/04-cannon.jpg

Annie Jump Cannon’s WorkAnnie Jump Cannon’s Work

Worked under Edward C. Pickering at Worked under Edward C. Pickering at Harvard University to classify spectra of Harvard University to classify spectra of starsstars

1911 - 1914: Created the Henry Draper 1911 - 1914: Created the Henry Draper Catalogue Catalogue

1918: Doctorate Degree1918: Doctorate Degree 1914: Honorary in the Royal Astronomical 1914: Honorary in the Royal Astronomical

SocietySociety

Spectral TypesSpectral Types

http://blueox.uoregon.edu/~courses/BrauImages/Chap17/FG17_010.jpg

Fig.16.18Fig.16.18

Fig.16.19Fig.16.19

Mass – Luminosity Mass – Luminosity

A star has a mass of 5MA star has a mass of 5M, how much brighter is , how much brighter is this star than the Sun?this star than the Sun?

280LL

MM5

LL

MM

LL

M5M

5.3

5.3

What is the Sun?What is the Sun?

Our nearest star.Our nearest star.

The center of our solar system.The center of our solar system.

The main engine for all the heat produced in The main engine for all the heat produced in the solar system.the solar system.

http://spaceflightnow.com/news/n0211/04soho/sun.jpg

What are the properties of the sun?What are the properties of the sun?

Distance: 1.49 X 10Distance: 1.49 X 108 8 km = 1 A.U.km = 1 A.U.

Size: 1.4 X 10Size: 1.4 X 1066 meter = 0.5° meter = 0.5°

Mass: 2 X 10Mass: 2 X 103030 kg kg

Density: 1.4 g/cmDensity: 1.4 g/cm33

Distance to the SunDistance to the Sun

Aristotle was the first person to consider the Aristotle was the first person to consider the problem. But Kepler was the first to obtain a problem. But Kepler was the first to obtain a precise measurement. precise measurement.

Recent measurements use radar bouncing Recent measurements use radar bouncing off other planets to obtain more precise off other planets to obtain more precise measurements.measurements.

Size of the SunSize of the Sun

Aristarchus was the first to consider the size of the Aristarchus was the first to consider the size of the Sun. Sun.

The modern method involves the angle of the light The modern method involves the angle of the light rays.rays.

150 Earths would fit along the diameter of the Sun.150 Earths would fit along the diameter of the Sun.

The Mass of the SunThe Mass of the Sun

Newton was the first person to find Newton was the first person to find accurately the mass of the sun with his accurately the mass of the sun with his theory of gravitation.theory of gravitation.

300,000X more massive than the Earth.300,000X more massive than the Earth.

The Density of the SunThe Density of the Sun

The density is simple calculation of the The density is simple calculation of the mass over the volume.mass over the volume.

The density is only 40 percent higher than The density is only 40 percent higher than water suggesting a gaseous composition.water suggesting a gaseous composition.

The Layers of a StarThe Layers of a Star

CoreCore Radiative ZoneRadiative Zone Convective ZoneConvective Zone PhotospherePhotosphere ChromosphereChromosphere CoronaCorona

http://www.conceptdraw.com/samples/samplestour/Proton/Proton.gif

http://www.uniba.sk/~ago/pics/sun/1907anim.gif

Sun FlareSun Flare

http://msowww.anu.edu.au/msovc/displays/images/sun-flare.jpg

Sunspot CycleSunspot Cycle

http://www.hao.ucar.edu/public/education/sp/images/sunspotn.2.jpg

Homework 7Homework 7 What is the luminosity of the Sun? What is the luminosity What is the luminosity of the Sun? What is the luminosity

of a O type star? And what the luminosity of the K type of a O type star? And what the luminosity of the K type star? How do they compare to the luminosity of the Sun? star? How do they compare to the luminosity of the Sun? And how much heavier is the O than the K type star?And how much heavier is the O than the K type star?

Two stars have magnitudes of 4 and 9 respectively. How Two stars have magnitudes of 4 and 9 respectively. How much brighter is the star with magnitude 4 than the star much brighter is the star with magnitude 4 than the star with magnitude 9? If these two star were the same with magnitude 9? If these two star were the same absolute magnitude (-4), how much further is the star with absolute magnitude (-4), how much further is the star with apparent magnitude of 9 than the star with the apparent apparent magnitude of 9 than the star with the apparent magnitude of 4?magnitude of 4?

Page 391, CQ 3, 12Page 391, CQ 3, 12 Describe the different layers of the Sun via their respective Describe the different layers of the Sun via their respective

temperatures and pressures. temperatures and pressures.