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Study of Stars and the Sun – unit 2.

This chapter is an astronomical study of stars and the sun.

Main Sequence Stars

– make up the majority of stars in our galaxy
– vary in size, mass and brightness
– convert H to He in their core, releasing lots of energy


– Largest stars in the universe
– Burn fuel fast, short lifespan

Red Giants

– a large, cool, luminous star
– in a later stage of evolution, no H remains in the core

Red Dwarfs

– Small, old, relatively cool star.
– Low mass/ slow fuel burning enables long-lasting life
– majority of starts in the galaxy

White Dwarfs

– small very dense star
– planet-sized
– Formed when low-mass stars exhaust all their central nuclear fuel and lose its outer layers

Neutron Stars

– Very small , very dense star
– Composed predominantly of closely packed neutrons.
– Formed after a supernova explosion of a massive star, however not massive enough to form a black hole


the explosion of a star, in which a massive star releases most of its mass

Black Hole

the end result of the collapse of a massive star after a supernova- the intense gravity of a black hole is such that nothing can escape, including light.

Stellar Nebula

Clouds of dust and gas scattered throughout the universe- the birthplace of stars

Planetary Nebula

A dying star sheds its outer layers of gas and dust

Describe the Life Cycle of a Main Sequence Star

In a stellar nebula, clouds of dust and gas swirl together and collapse under their own gravity, forming stars. When nuclear fusion ceases in the core (some billions of year later) a main sequence star will expand and become a red giant. Then, the star will shed its outer layers of gas and dust, eventually becoming a white dwarf star.

Describe the Life Cycle of a Giant Star

In a stellar nebula, clouds of dust and gas swirl together and collapse under their own gravity, forming stars. Giant starts expend a lot of energy very quickly. When nuclear fusion ceases in the core,a giant star will expand further and become a red supergiant. Then, most massive stars will explode violently in a supernova. The final result depends on the mass of the giant star. Sufficiently massive stars will collapse on themselves completely and form black holes- small, dense stars whose gravity is so strong that light cannot escape it. If the giant star is not sufficiently massive, it can form a neutron star, made up of densely packed neutrons with extremely strong gravity.

How are stars organized by scientists

Hertzsprung-Russell diagrams (developed by its namesake scientists) was created when Hertzprung and Russell graphed their data and noticed a trend in the size, temperature, color and luminosity of stars.

our star the sun

– The sun is a yellow dwarf, main sequence star
– The sun is in the Orion arm orbiting the center of the Milky Way Galaxy
– We (the earth) are about 93 million miles from the sun

The sun impacts the earth by…

– providing all the energy for the planet
– drives seasons, ocean currents, weather, climate, aurorae

Structure of the Sun: the core:

-produces all the sun’s light and heat
– The temperature and pressure are so great that nuclear fusion occurs here
– produces tremendous amounts of energy through nuclear fusion

nuclear fusion is…

– the process in which intense heat and pressure fuses the nucleus of two Hydrogen atoms into Helium, releasing a tremendous amount of energy.
– This process is responsible for the energy that a star releases, and takes place in the core of stars.
– without this process, stars eventually die

Structure of the Sun: Radiative Zone

– In this zone, energy from the core travels outward
– This region is so dense it takes about 150,000 years to work its way through

Plasma is…

a 4th state of matter in which a gas behaves viscously like a liquid- meaning it has some properties of a liquid, but is actually a gas.
This is due to the large quanities of ions

Structure of the Sun: Convection Zone

– In this zone, rising and falling currents carry heat from the radiative zone to the surface.
– Similar to boiling water or an oven

How does convection carry heat?

– Heat energy rises to the top, where is cools and falls back down to the heating element.
– this churning motion of rising and falling is very effective in evenly heading the area

Structure of the Sun: Photosphere

– What our eyes percieve as the visible surface of the sun.
– In this level, energy escapes from the interior and streams into the sun’s atmosphere and beyond
– home to sunspots and flares

Sunspots are:

Dark areas on the sun’s surface
– cooler than the area around them
-due interactions between the sun’s materials travelling in the path of its magnetic field, cooling, then falling

Flares are:

explosions on the sun that spew energy into space.
– extend past the photosphere into the Chromosphere

Structure of the Sun: Chromosphere

– Turbulent layer of the sun’s atmosphere just above the photosphere
– flares and prominences extend into this layer
– gives off most of the sun’s UV light

Structure of the Sun: Corona

– The Sun’s outer atmosphere
– luminous white halo visible only during a solar eclipse
– Much hotter than the photosphere
– produces x-rays