The Sun... And Other Stars! Star Classification:

Sun Stats; Mass: 333,000 times greater than Earth; ~ 2.0 x kg Composition: 73% hydrogen 25% Helium 2% ‘other’ (oxygen, carbon, etc.) Surface Temp: ~ 5800 K Rotation: 27 Days We rotate in 1 day! Diameter: 1,392,000 km That’s 109 times greater than Earth!

Sun’s Energy The Sun’s energy comes from nuclear fusion – when light hydrogen nuclei combine to form heavier helium nuclei. These reactions occur in the Sun’s core The Sun should have enough fuel to continue burning for about 5 billion more years; nothing we need to worry about!!

Sun’s layers, from inside out: Core Site of fusion Radiative Zone Converts energy from fusion reaction to radiation Convective Zone Convection currents carry energy to surface Photosphere Emits most light radiation

A plain, old, mediocre star... Scientists describe the physical properties of other stars in the universe by comparing them with the physical properties of the Sun. The physical properties of stars are: Mass, density, diameter, magnitude, luminosity, and surface temperature. Magnitude is the brightness of stars; the brighter the star, the lower its magnitude. Luminosity is the brightness of a star compared to the Sun, with the Sun being 1. Anything brighter than the sun is >1, anything dimmer is <1.

Hertzsprung-Russell (H-R) Diagram The H-R diagram classifies stars according to their luminosity (absolute magnitude) and spectral class based color and surface temperature.

Life cycle of the Sun The Sun is at the mid-life point of its predicted 10 billion year life. It started as a nebula and is now at the main sequence stage where fusion will continue until the hydrogen is used up. The Sun will then enter the Red Giant phase where it expands and grows cooler and more luminous. Its final stage is white dwarf, after it collapses upon itself and only the hot, dense core will remain.

Sun’s life cycle... From nebula to main sequence to red giant to white dwarf

Let’s look at vocab: H-R Diagram: Diagram that classifies stars according to their luminosity/absolute magnitude, and spectral class based on color and surface temperature. Luminosity: The brightness of a star compared to the Sun. Absolute Magnitude: Compares the brightness of stars from a standard distance from Earth.

More vocab... Apparent magnitude: How bright a star appears to be from Earth ~ not very ‘scientific’. Main Sequence: Average, ordinary stars. ~ 90% of stars are main sequence. Supergiant: 20 to 200 times larger than the Sun, but also much brighter, cooler and less dense. Dwarf: Small stars; fairly hot but very dim. Diameter is about the same as Earth, but their mass is equal to the sun...

Star color; As stars get cooler, then change from blue to red. Red = cooler stars, Blue = Hotter stars White dwarfs are dim because they are so small. Red giants are bright because they are so big. In order for a cool star to be bright, it must have a very large diameter.

Deneb & Rigel ~ Nearby supergiants If Deneb and Rigel were as close as the Sun, they would appear exceptionally bright! Deneb and Rigel are about 100,000 brighter than the sun!!