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