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10: The Sun

Last updated

Jul 23, 2025
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- 9.20: Eris
- 10.1: What do you think?

Lumen Learning
Lumen Learning

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“Here Comes the Sun
Here comes the sun
Here comes the sun,
and I say, It’s all right
Little darling
It’s been a long, cold lonely winter
Little darling
It feels like years since it’s been here”
…
Sun, sun, sun, here it comes

George Harrison
The Beatles
Abbey Road, 1969

Learning Objectives

Upon completion of this module, the student will be able to:Upon completion of this module, the student will be able to:

Describe the production of energy and light through the proton-proton cycle
Be able to identify the Sun’s regions
Be able to identify the Sun’s solar features
Overview how we study the Sun
Identify the potential dangers it can pose to Earth

This module overviews our star, the Sun, how light and energy are produced, the various solar regions and features, and how we observe the Sun.

10.1: What do you think?
This page discusses the hypothetical scenarios of Earth in the orbits of Venus and Mars. If in Venus's orbit, Earth would experience extreme heat and a dense atmosphere, jeopardizing life. In contrast, Mars's orbit would lead to colder temperatures and a thinner atmosphere, posing additional challenges for life.
10.2: Fission and Fusion
This page explains the difference between fission and fusion, two opposing nuclear processes. Fission splits large atomic nuclei into smaller ones, releasing energy and free neutrons, often leading to a chain reaction, while fusion combines smaller nuclei to form larger ones at extremely high temperatures, also releasing energy. Most fission products are radioactive, highlighting the distinct characteristics and conditions under which each process occurs.
10.3: Our Star, the Sun
This page discusses the sun as the central star of our solar system, highlighting its proximity to Earth compared to Proxima Centauri. It takes light 8.3 minutes to travel from the sun, which experiences changes in energy and brightness affecting Earth. Understanding these dynamics is vital for astrophysics and reveals insights about other stars. The sun's photosphere vibrates from sound waves within its gases, allowing scientists to study its interior.
10.4: How the Sun Works
This page clarifies the misconception that the sun 'burns.' Instead, it explains that the sun generates energy through the proton-proton cycle, and highlights that it takes about 100,000 years for this energy to travel from the sun's core to its surface.
10.5: A “Quick Guide” to Solar Fusion—The Proton-Proton Cycle
This page explains the Proton-Proton Cycle as the main energy source for stars like the sun, involving the fusion of protons to form helium while releasing energy. It accounts for 85% of the sun's energy and will continue until hydrogen is depleted. More massive stars use the CNO cycle, leading to iron formation, which halts further fusion. Neutrinos from these reactions provide evidence of solar fusion processes.
10.6: Solar Regions
This page details the sun's four main regions: the Core, where nuclear fusion occurs at approximately 15 million degrees; the Radiative Zone, which transports energy through light; the Interface Layer, thought to generate the sun's magnetic field; and the Convective Zone, covering 70% of the sun's radius, where energy transfer occurs via convection with heated fluids rising and cooler ones descending.
10.7: Major Solar Features
This page discusses the sun's structure, focusing on the Photosphere as its visible layer, characterized by faculae, granulation, and sunspots from magnetic disturbances. It also covers the chromosphere and prominences, alongside solar flares and the corona, which emits solar wind and can create coronal mass ejections that impact Earth.
10.8: Studying the Sun
This page emphasizes the safe observation of the sun's features, particularly during solar eclipses, and the necessity of using proper filters to protect eyesight. It mentions historical contributions, such as Frauenhofer's discovery of absorption lines in the sun's spectrum, and describes various observation methods for studying solar phenomena like flares and prominences.
10.9: The Dark Side of the Sun
This page discusses the sun as a variable star with cycles that impact global climate, although the connection to Earth's climate is complex. Low solar activity may have played a role in past cooling events like the Little Ice Age. Additionally, solar flares and Coronal Mass Ejections (CMEs) pose risks to electrical infrastructure and satellites, with historical examples highlighting potential catastrophic outcomes.
10.10: The National Solar Observatory
This page describes the Richard B. Dunn Solar Telescope at the National Solar Observatory, which is 136 feet tall and 356 feet long, with some underground components. It achieves 0.2 arc-second resolution for high-quality solar imagery and has undergone upgrades with adaptive optics to improve observation by reducing atmospheric interference.
10.11: NASA’s Heliophysics Science Division
This page outlines NASA's Heliophysics Science Division, which focuses on studying the sun, heliosphere, and their interactions with Earth and other planets. The division examines geospace, including Earth's upper atmosphere, ionosphere, and magnetosphere, along with environmental changes in the heliosphere tied to Solar System weather. It operates under the National Aeronautics and Space Administration at the Goddard Space Flight Center.

Learning Objectives

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