Class Notes for Module 11

8.E 5.5 Physical Properties of Stars

Student Expectation                                                                             

The student is expected to describe and classify specific physical properties of stars: apparent magnitude (brightness), temperature (color), size, and luminosity (absolute brightness).

Advanced Student Expectation:The students are expected to explain the physical properties of the Sun and its dynamic nature and connect them to conditions and events on Earth.


Key Concepts                                                                                                  

A star is a large ball of gas that generates its own energy and is held together by its own gravity.

Stars emit a tremendous amount of energy and some in the form of light.

Stars come in a variety of sizes and compositions which determines their amount of energy and gravity.

Advanced: The Sun is a medium-sized star that is the closest star to Earth; it is hundreds of thousands of times closer than any other star. It takes 8.3 minutes for light to travel from the Sun to Earth.

Advanced: The Sun is composed of six layers: the outermost layer, the corona; the chromosphere; the photosphere; the convective zone; the radiative zone; and the core, which is the innermost layer.

Advanced: Sunspots, solar flares, solar wind, coronal mass ejections, and prominences interact with Earth’s magnetic field and atmosphere. This can damage electrical equipment, including radios, televisions, and cell phone signals.

Advanced: Solar wind sends charged particles into the solar system, including Earth.


Fundamental Questions                                                                                 

What is a star?

What are the characteristics of a star?

How can you figure out the properties of a star?

Advanced: What are some physical properties of the Sun?

Advanced: How can events on the Sun impact Earth?

Advanced: How does the Sun provide energy for Earth?


8.E 5.6 Modeling Solar Properties

Student Expectation

The student is expected to create models of solar properties including rotation, structure of the Sun, convection, sunspots, solar flares, and prominences.


Key Concepts

The Sun has six regions: the core, the radiative zone, the convective zone in the interior, the visible surface (the photosphere), the chromosphere, and the outermost region, the corona.

The energy produced in the core powers the Sun and produces essentially all the heat and light we receive on Earth.


Heat from inside the Sun is carried up by columns of hot gas in the convective zone, which starts at around 70% of the Sun’s radius and goes to the outer surface (the photosphere).

The Sun’s visible surface is called the photosphere, a 500-kilometer-thick (300-mile-thick) region, from which most of the Sun’s radiation escapes outward and is detected as the sunlight we observe here on Earth about eight minutes after it leaves the Sun.

Sunspots in the photosphere are areas with strong magnetic fields that are cooler, and thus darker, than the surrounding region.


Prominences rise up through the chromosphere from the photosphere, sometimes reaching altitudes of almost 161,000 kilometers. These gigantic plumes of gases, often in a loop shape stretching from one side of a sunspot to the other, are the most spectacular of the solar phenomena. Prominences contain much cooler plasma and emit quite a bit of light.

Solar flares occur when magnetic energy that has built up in the solar atmosphere is suddenly released. Solar flares also produce bursts in the solar wind.


Fundamental Questions

What are the benefits and limitations of a model of the Sun?

What are solar properties?

What is the structure of the Sun?

How does the Sun behave?

When creating a model of the solar properties, what should the model demonstrate?


The Hertzsprung Russell Diagram

The most famous diagram in astronomy is the Hertzsprung-Russell diagram. This diagram is a plot of luminosity (absolute magnitude) against the colour of the stars ranging from the high-temperature blue-white stars on the left side of the diagram to the low temperature red stars on the right side.

-----------------------------------------------------------------------------------------------------------------------------------------------------------------------------Models of the Sun


♦ Astronomical bodies from largest to smallest are:

Universe, →galaxy, →solar system, →nebula, →star, →planet, →moon, and →asteroid.


♦ The inner planets (Mercury, Venus , Earth and Mars) are all relatively close together while the outer planets (Jupiter, Saturn, Uranus and Neptune ) are much more spread out.


♦ Meteors, Earth and Venus have rocky surfaces, unlike the Sun, Jupiter, and nebulae which are primarily gaseous.


 Galaxies are collections of stars, gas, and dust. They are held together by their mutual self-gravity. Nebulae are found inside galaxies, filling the space between stars or enveloping stars�like a cloak. They're made of dust and gas and can appear as either bright or dark clouds. The gas is mostly hydrogen mixed with some helium. Galaxies and nebulae differ greatly by their size and while, galaxies posses many stars, a nebula is just the beginning or end of one star.


♦ The closer a planet is to the Sun, the faster it needs to travel in order to maintain its orbit.


 Comets are balls of ice and dust in orbit around the Sun. The orbits  of comets aredifferent from those of planets - they are elliptical. A comet's orbit takes it very close to the Sun and then far away again.


♦ Despite being closer to the sun, Mercury is not the hottest planet in the solar system as the planet Venus holds this title.


♦ Venus is the second planet from the sun and the hottest in the solar system. Its temperatures can reach 464 degrees Celsius. Ever since the disqualification of Pluto as a planet, Neptune is considered the coldest planet with an average temperatures of -200 degrees Celsius.


♦ Venus is so hot because it is surrounded by a very thick atmosphere which is about 100 times more massive than our atmosphere here on Earth.


 Planets Farthest From The Sun Have The Coolest Surface Temperatures.