The Sun and Stars

The Life Cycle of Stars

There are three types of galaxies, Spiral, Irregular, and Elliptical. What shape is our galaxy?

Our galaxy, the Milky Way galaxy, is a spiral galaxy that looks somewhat like a pinwheel.

​Our Galactic Home

​The Milky Way Galaxy

Stars and the HR Diagram

• The HR Diagram is a graph that compares the surface temperature of a star with its magnitude or how bright the would be if they were all the same distance from Earth.

• Luminosity is a term that measures how much energy leaves a star in a certain period of time.

• General Rule: As luminosity increases, brightness increases.

What do the axes on this chart show us about stars?

Temperature

Luminosity

Spectral Class

Magnitude

What affects luminosity?

• Temperature: As temperature increases, luminosity increases.

• Size: As size increases, luminosity increases.

• Most Luminous? Large and Hot

• Least Luminous? Small and Cool

Multiple Choice

What is the approximate surface temeprature of the sun according to the HR diagram?

• 5,500 K

• 6,000K

• 7,200 K

• 15,000K

Multiple Choice

Would the surface temperature of a red supergiant be higher or lower than a white dwarf?

• Higher

• Lower

Poll

What is the color of the stars with the highest surface temperature?

• Red

• Yellow

• White

• Blue

Multiple Choice

Most of the stars on the HR diagram are classified as which type of star?

• White Dwarfs

• Main Sequence

• Giants

• Supergiants

Multiple Choice

How is it possible for white dwarf stars to have a lower luminosity than the sun, even though the sun has a cooler surface temperature.

• The sun is smaller than a white dwarf.

• The sun is larger than a white dwarf.

Multiple Choice

Star A has a surface temperature of 10,000K and medium brightness. What color is it?

• White

• Red

• Yellow

• Blue

Multiple Choice

What kind of star is Sirius, the Dog Star?

• Main Sequence

• White Dwarf

• Blue Giant

• Red Supergiant

Multiple Choice

What kind of star is Sirius, the Dog Star?

• Main Sequence

• White Dwarf

• Blue Giant

• Red Supergiant

The Life Cycle of a Star

• All stars begin life as dust in a nebula.

• Gravity begins to form masses of hydrogen in the nebula.

• When the heat in the protostar reaches 15,000,000 C, nuclear fusion starts and a star is born!

This is the Pillars of Creation within the Eagle Nebula, part of M16, viewed by the Hubble Telescope

2 Pathways:

The mass of the star that forms in the nebula determines how the star will burn fuel:

--small stars burn their fuel more slowly and reach lower temperatures.

--large stars burn through their fuel rapidly and reach higher temperatures.

Common Ground:

All Stars begin life as a H -> He fusing Main Sequence star.

No matter the mass of a star, as its hydrogen supply begins to run low, the core cools and the star takes on a red color, forming either a Red Supergiant or a Red Giant.

Different Endings:

Large stars can end up as black holes or pulsars.

Small stars can end up as a Nova, Supernova or a Black Dwarf.

Multiple Choice

If all Main Sequence stars are "young" stars, what can the color tell you about the star?

• Its size

• how long it will stay part of the Main Sequence

• Both options are correct

• Neither option is correct