Ch. 12 Lesson 1 Stars

What are stars? A star is large ball of gas that emits (gives off) energy produced by nuclear reactions in the star’s interior. This energy is electromagnetic radiation. One example of this is visible light. Objects in the solar system reflect off this light.

The structure of stars Layered structure Energy is produced at the core (dense & high temperature. The core has plasma. Energy from the core travels to the photosphere (where light is emitted). The photosphere of the sun is the part we see.

Types of Stars Stars come in difference sizes, masses, and temperatures. Star TypeDiameter (1 = sun’s diameter) Mass (1 = sun’s mass) Surface Temperature (Kelvin) Supergiant variable Red Giant Main Sequence White Dwarf ,000-6,000 Neutron Star Variable

The distance between stars Recall that one a.u. = the distance between the Earth and the Sun. 1 a.u. = 150,000,000 km. Stars are even farther away! We use the light-year to measure star distances (since they give off light). A light year is the distance light travels in one year. 300,000 km/sec. Equal to 9,500,000,000,000 km

What are stars made of? We can only study the light they emit (because they are so far away). Spectroscopes use color to analyze what a star is made of. ROYGBIV is used (a continuous spectrum – rainbow of light). Absorption spectrum shows dark lines. The dark lines tell you what elements are present in cooler gas.

Elements in a Star Each element shows a difference set of lines. Like a fingerprint. The more absorption lines, the more elements are present. Most stars are made of hydrogen and helium. Trace elements occur (carbon, nitrogen, oxygen, can occur).

Temperature & Color of stars Red stars have temperatures of almost 3500 K. Yellow stars are around 5000 K (Our Sun) White stars are around 7000 K Blue stars are around K Red has longest wavelength & Blue has shortest wavelength.

Brightness & Distance The closer a star is the brighter it is. Luminosity is the amount of light energy emitted per second. We use Watts as the unit of luminosity. E.g. 100-Watt light bulb. Stars emit much more Watts.

Apparent vs. Absolute Apparent magnitude is how bright a star is from Earth. Absolute magnitude is how bright a star is at a distance away from Earth (say from the Hubble telescope) The brighter the star, the smaller the number. E.g. a star of magnitude of 1 is.2.5 times brighter than one that has a magnitude of 2.

Hertzsprung-Russell Diagram (H-R Diagram)