The Sun

&

Stars, Galaxies, & the Universe

Composition & Age of the Sun

• Hydrogen and helium make up over 99% of the sun’s mass.• About 75% of the sun’s mass is hydrogen• Traces of all other elements make up about 1% of the

sun’s mass

• Scientists estimate the sun’s age to be ~ 5 billion years old

Structure of the Sun

• The Sun has layers which can be compared to the Earth’s core, mantle, crust, and atmosphere

• All of these layers except the core has a unique name as a part of the sun

Structure of the Sun (continued)

• Core = Center of the Sun, comparable to the inner core on Earth

• Radiative Zone = Layer surrounding the core, similar to the Earth’s outer core

• Convective Zone = Similar to the Earth’s mantle

Structure of the Sun (continued)

• Photosphere = The surface of the sun. Equivalent to the Earth’s crust. The photosphere is what we see from Earth.

• Chromosphere = The Sun’s atmosphere. The uppermost part is known as the corona

Sunspots

• Sunspots are cool, dark areas of gasses in the photosphere caused by magnetic fields

• Sunspot cycles are variations in the number of sunspots which occur on average every 11 years

Structure of the Sun

Stars

• A star is a ball of gases that gives off a tremendous amount of electromagnetic energy in the form of heat and light

• A star’s energy comes from nuclear fusion• Nuclear fusion forces light atomic nuclei to combine to form

heavier atomic nuclei and release energy

• Stars can vary based on mass, composition, temperature, distance from Earth, brightness, and color

Nuclear Fusion

Classifying Stars

• Stars are classified based on their color / temp and brightness

• Stars are plotted on a chart called an H-R diagram• The brightness of a star is plotted on the vertical axis

• Brightness depends on how big a star is

• The temperature and color are plotted on the horizontal axis

• Blue is hottest; red is coolest

H-R Diagrams

• The plot of stars on an H-R diagram reveals a consistent pattern of stars

• Most stars fall in a band which runs diagonally through the diagram; this is the main sequence• The sun is a main sequence star

• Other categories of stars are based on where they are found on the H-R diagram• White dwarfs, red dwarfs, red giants, and red super

giants

Hertzsprung-Russell Diagram

H-R Diagram, Figure 1, pg 781

Star Groups

• Galaxies – contain the greatest amount of stars; approx 100 billion• Our solar system is located in the Milky Way galaxy• The Milky Way is a spiral galaxy

• Globular Clusters – contain hundreds of stars

Star Groups

• Binary Systems – pairs of stars (2) which revolve around each other

• Constellations – fixed patterns of stars as seen from Earth• There are 88 constellations which help to divide the

sky & describe the location of celestial objects

Constellations

The Universe

• The universe the sum of all space, matter, and energy that exists.

• Most of the universe is empty space: a vacuum

Expansion of the Universe

• The universe is expanding.

• Stars show a red shift.

• Red shift is an apparent shift toward longer wavelengths of light caused when an object moves away from the observer

Red Shift

Structure of the Universe