StarsStars

What is a star? The objects that heat and light the planets in a system A star is a ball of plasma held together by its own gravity –Nuclear reactions occur in stars (H  He) –Energy from the nuclear reactions is released as electromagnetic radiation

Characteristics of Stars DISTANCE –Measured in light-years The distance which a ray of light would travel in one year

Characteristics of Stars Magnitude (brightness) –A measure of brightness of celestial objects Smaller values represent brighter objects than larger values –Apparent magnitude How bright a star appears to be from Earth –Absolute magnitude (luminosity) How bright a star actually is

Characteristics of Stars Temperature & Color –The color of a star indicates the Temperature of the star –Stars are classified by Temperature Decreasing Temperature (bright to dim) O, B, A, F, G, K, M [Oh Be A Fine Girl, Kiss Me ]

Hertzsprung-Russell Diagram

Main Sequence Stars A major grouping of stars that forms a narrow band from the upper left to the lower right when plotted according to luminosity and surface temperature on the Hertzsprung-Russell diagram

Types of Stars Classification ClassTemperatureColor O20, ,000 KBlue B10,000 – 30,000 KBlue-white A7,500 – 10,000 KWhite F6,000 – 7,500 KYellow-white G5,000 – 6,000 KYellow K3,500 – 5,000 KOrange M2,000 – 3,500 KRed

Stars: large ball of gas held together by gravity with a core so hot that nuclear fusion occurs Super Giant Stars: bright stars with a mass more than 10 times higher than that of our sun and have started to die. Giant Stars: start out with a mass about 0.8 to about 10 times the solar mass of our sun. White dwarf stars: white dwarf hot, dense, slowly cooling sphereSize

Life Cycle of Stars

Life Cycle of Stars Begin their lives as clouds of dust and gas called nebulae Gravity may cause the nebula to contract Matter in the gas cloud will begin to condense into a dense region called a protostar The protostar continues to condense, it heats up. Eventually, it reaches a critical mass and nuclear fusion begins. Begins the main sequence phase of the star Most of its life in this phase

Life Cycle of Stars Life span of a star depends on its size. –Very large, massive stars burn their fuel much faster than smaller stars – Their main sequence may last only a few hundred thousand years –Smaller stars will live on for billions of years because they burn their fuel much more slowly Eventually, the star's fuel will begin to run out.

Life Cycle of Stars: Death Average stars expand into what is known as a red giant Massive stars will become red supergiants This phase will last until the star exhausts its remaining fuel At this point the star will collapse

Life Cycle of Stars