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Be humble, for you are made of dung. Chapter 30 – Stars. Be noble, for you are made of stars. SERBIAN PROVERB. 30.1 The Sun . OBJECTIVES Explore the structure of the Sun. Describe the solar activity cycle and how the Sun affects the Earth. Compare the different types of spectra. .

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chapter 30 stars

Be humble, for you are made of dung.

Chapter 30 – Stars

Be noble, for you are made of stars.


30 1 the sun
30.1 The Sun
    • Explore the structure of the Sun.
    • Describe the solar activity cycle and how the Sun affects the Earth.
    • Compare the different types of spectra.
sun s properties
Sun’s Properties
  • Sun
  • All stars, including the Sun, have the following identical composition:
  • 25 percent helium
  • 73 percent hydrogen
  • and 2 percent other
the sun
The Sun

The Sun contains 99 percent of the mass in the solar system, it controls the motion of the planets.

the sun1
The Sun

- The scale

Just how

big ?

sun s structure
Sun’s Structure

The solar interior is not solid, but gaseous, because of its high temperature.

Other than the use of special instruments, the chromosphere is only visible during a solar eclipse when the photosphere is blocked.

sun s interior
Sun’s Interior

In the convective zone of the solar interior, volumes of gas carry energy to the Sun’s surface.


The outermost layer of the Sun’s surface from which most of the light emitted by the Sun comes is the photosphere.


The photosphere is the Sun's visible surface, due to its high temperature, it glows yellow.


The top layer of the Sun’s atmosphere is the low-density corona.

solar wind
Solar Wind

The solar wind flows outward from the corona to the entire solar system.

solar activities


Solar Activities

Solar activity cycle is minimum to maximum sunspots over a period of 22.4 years.

Due to a reversal of polarity.

Sun spots are caused by magnetic fields

solar activities1
Solar Activities

In the 1600s, the solar activity cycle stopped, and there were no sunspots for nearly 50 years.

No sun spots equaled mini ice-age!


A prominence is an eruption of hot gas that can extend thousands of Km into space from the surface of the Sun before cooling and condensing and then rains back to the surface.

solar flares
Solar Flares

Earth is bombarded with particles and radiation after violent eruptions from the Sun’s surface called solar flares.

energy output
Energy Output

The energy that reaches our planet from the sun is 1354 J/m2/sec

That’s enough to operate ~10 - 100 Watt bulbs within each 1-m2 area.


The Spectrum is visible light arranged according to wavelengths.

emission spectrum
Emission Spectrum

A non-compressed gas produces a spectrum in which you see bright lines at certain wavelengths, this is called an emission spectrum.

absorption spectrum
Absorption Spectrum

The dark bands observed in a solar spectrum are caused by different chemical elements which absorb light at specific wavelengths.

30 1 why does the sun shine quiz 10 pts
30.1 Why does the sun shine ?Quiz (10 pts)

With the help of TMBG! ,

On Paper

30 2 measuring the stars
30.2 Measuring the Stars
    • Describe star distribution and distance.
    • Classify the types of stars.
    • Summarize the interrelated properties of stars.

Ursa Major “Big Dipper”


Polaris “North Star”


A group of bright stars named for an animal, a mythological character, or an everyday object is called a constellation.


W072, N42

binary stars
Binary Stars

A star that is gravitationally bound to another star can either be part of a star cluster or a binary star.

Astronomers can sometimes identify binary stars even if only one star is visible.

speed of light
Speed of Light

The speed of light is:

(670,616,629 mph)

299,792.458 km/s

The Speed of Light:

It’s Not Just A Good Idea

It’s the Law.


Light-year (ly)  Distance traveled by light in one year

9.461X 1012 Km

Parsec (pc)  3.26 ly, or . . .

3.086X 1013 Km


The apparent shift in a star’s position caused by the motion of the observer is called parallax.

Using the parallax technique, astronomers can accurately measure the distance of stars up to 500 pc away.


One of the most basic observable properties of a star is brightness, the classification was established by the ancient Greeks.

apparent magnitude scale
Apparent Magnitude Scale

In the modern classification of apparent magnitude, a difference of 5 magnitudes corresponds to a factor of 100 in brightness.

absolute magnitude
Absolute Magnitude

Absolute magnitude takes distance into account when indicating the brightness of a star.

apparent absolute magnitude
Apparent & Absolute Magnitude

Both classify the brightness of stars.



takes into account differing distances and measures brightness at a distance of 10 parsecs.

  • how bright a star appears to be.
hertzsprung russell diagram
Hertzsprung-Russell Diagram

The Hertzsprung-Russell diagram (H-R) diagram, first plotted in the twentieth century, demonstrates the relationship of luminosity and temperature.

O – B – A – F – G – K – M

spectral sequence
Spectral Sequence

Stars are assigned a spectral type, with M being the coolest stars.

main sequence
Main Sequence

The section of the H-R diagram into which about 90 percent of stars fall is called the main sequence.

30 3 stellar evolution
30.3 Stellar Evolution
    • Explainhow astronomers learn about the internal structures of stars.
    • Describe how the Sun will change during its lifetime and how it will end up.
    • Compare the evolutions of stars with different masses.

Nebula is a cloud of interstellar gas and dust that collapses on itself to form a new star.

hydrostatic equilibrium
Hydrostatic Equilibrium

One principle used by astronomers to understand the basic structure of stars is hydrostatic equilibrium .


Fusion is combining of lightweight nuclei into heavier nuclei, such as four hydrogen nuclei combining to form a helium nucleus.

Stars on Main Sequence all produce energy by fusing

internal composition
Internal Composition

As a star ages, its internal composition changes as nuclear reactions in the star’s core convert one element into another.

May Fuse

Helium  Carbon

Carbon  Oxygen

star s mass
Star’s Mass

Only 10% of a star's mass undergoes fusion because temperatures outside of the core never get hot enough for reactions to occur.

life cycles what happens next
Life Cycles - What happens next?

What happens next ? depends on the...


stellar life cycles
Stellar Life Cycles

The main sequence lifetime of a low-mass star is much longer than the lifetime of the Sun.

helium reaction phase

The helium-reaction phase for a star the size of the Sun lasts only one-tenth as long as the hydrogen-burning phase. The result is a core made of carbon and it is a white dwarf.

helium reaction phase1

Following the end of each reaction stage, a massive star becomes a red giant several times.

black holes
Black Holes

When the core of a star collapses forever, the extremely dense object that remains is called a black hole.

is a small, massive, dense object that has a gravity so immense that nothing—not even light—can escape it.

fission fusion both are atomic reactions that produce energy
Fission & FusionBoth are atomic reactions that produce energy



  • is the process of splitting heavy atomic nuclei into smaller, lighter atomic nuclei
  • is the combining of lightweight nuclei into heavier nuclei
  • much more energy being released