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

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.