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Stars and the Sun. BC Science Probe 9 Section 13.3-13.4 Pages 425-436. Stars. Stars have a life cycle. Beginning (birth) Midlife End (death) The Sun, which is the star closest to us, has been around for 5 billion years and is expected to last another 5 billion years. Stellar Birth.

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Stars and the sun

Stars and the Sun

BC Science Probe 9

Section 13.3-13.4

Pages 425-436


  • Stars have a life cycle.

    • Beginning (birth)

    • Midlife

    • End (death)

  • The Sun, which is the star closest to us, has been around for 5 billion years and is expected to last another 5 billion years.

Stellar birth
Stellar Birth

  • Stars are born when nebulas collapse on themselves.

    • Small amounts of matter collide and stick together making bigger masses that have more gravity.

Stellar birth1
Stellar Birth

  • When the nebula begins to collapse, the region with the greatest density will pull more of the hydrogen gas toward it than the rest and will begin to grow.

  • This is called a protostar.

Stellar birth2
Stellar Birth

  • Once the protostar gains enough mass and gets dense enough, that material in the centre will become hot enough to start nuclear fusion!

Nuclear fusion
Nuclear Fusion

  • This happens in the core of the star.

  • Hydrogen nuclei fuse together to form helium nuclei.

  • 6 hydrogen protons fuse to produce 1 helium nucleus with 2 protons and 2 neutrons as well as 2 free protons and a ridiculous amount of energy!

  • The energy can be in the form of heat, light, x-rays, gamma rays and particles.

Nuclear fusion2
Nuclear Fusion

  • The energy of the nuclear fusion causes thermal expansion.

    • The force of the expansion counters and balances the gravity to stop the collapse.

  • Our Sun went through this process. It probably took 30 million years to condense and ignite.

Stellar midlife
Stellar Midlife

  • The fusing of hydrogen to helium continues just like what is happening in the Sun right now.

  • The energy that is released can take thousands of years to reach the outer layers of the Sun where it is released as light.

Solar anatomy
Solar Anatomy

  • The part of the Sun that produces the energy is the core.

    • Temp. - 1.5 x 107 ⁰C

    • Radius – 1.75 x 105 km

Solar anatomy1
Solar Anatomy

  • The next layer of the Sun is the radiative zone.

    • 3.5 x 105 km thick

Solar anatomy2
Solar Anatomy

  • The outer layers of the Sun are the convective zone and the photosphere.

  • Convective zone

    • 2 x 105 km thick

    • 2 x 106 ⁰C

  • Photosphere – the visible part of the Sun

    • 300 km thick

    • 5500 ⁰C

Solar anatomy3
Solar Anatomy

  • The layers all rotate at different speeds and once the energy reaches the convective zone, it moves by convection currents to the surface.

Solar anatomy4
Solar Anatomy

  • Outside of the photosphere are the chromosphere and the corona.

  • Chromosphere

    • Layer of gases at 60 000 ⁰C

  • Corona

    • Layer of gases at 2 x 106 ⁰C

The sun s surface
The Sun’s Surface

  • The surface of the Sun is not smooth and featureless.

  • It looks more like the surface of a boiling liquid.

The sun s surface1
The Sun’s Surface

  • Sunspots

    • Dark spots on the surface of the Sun.

    • The vary in size and regularity.

    • Caused by disturbances in the Sun’s magnetic field.

    • They appear in pairs with opposite magnetic poles which disturb the magnetic field more.

    • The magnetic disturbances caused by sunspots can lead to solar flares and solar prominences.

The sun s surface2
The Sun’s Surface

  • Solar prominences

    • 1 x 1011 tonnes of glowing hydrogen released from the photosphere.

    • Last 4-5 minutes

The sun s surface3
The Sun’s Surface

  • Solar flares

    • Ejection of large quantities of gas and charged particles.

    • Last a very short time

The sun s surface4
The Sun’s Surface

  • Solar wind

    • This is happening all the time.

    • Ionized gas emitted from the Sun.

    • Stronger when there are flares and prominences.

    • Creates aurora borealis.

    • Disrupts communications equipment and other electronic systems.