Our Universe Stars Different Types of Stars A

Our Universe

Stars

Different Types of Stars A. Giants D. Supergiants B. White Dwarfs E. Sun C. Main Sequence

Sagittarius Star Cloud, HST Star Color v Stars have different colors Some look red (like Betelgeuse), some look more yellow (like the Sun), and some look blue or blue-white (like Sirius) Color is directly related to temperature v Light is not sensitive to the details of the star's composition but to its temperature (according to which law? ) v Astronomers can determine: 1. the surface temperature of a star by measuring its color 2. the composition of its outer layers by looking at its spectral lines Sun

Star color and brightness v Is a star’s color (temperature) related to its size? v Is the relation the same for all stars? v Are there different kinds of stars?

Electromagnetic Radiation Energy that travels through space in waves Ø Stars give off electromagnetic radiation in different forms Ø Each form has its own wavelength Ø Radio Waves Ø Infrared Rays Ø Visible Light Ø Ultraviolet Light Ø X-Rays Ø Gamma Rays Ø

Continuous spectrum and Absorption spectrum Ø A Any visible white light consists of millions of colors, including the seven very obvious colors: red – orange – yellow – green – blue – indigo and violet. Ø A hot glowing object like a wire inside the bulb gives off a continuous spectrum. Ø A continuous spectrum is a spectrum that shows all colors.

Continuous Spectrum Ø A rainbow is an example of a continuous spectrum. Most continuous spectra are from hot, dense objects like stars, planets, or moons. . Any solid, liquid and dense (thick) gas at a temperature above absolute zero will produce a thermal spectrum.

Absorption Spectrum Ø Because each element in this world absorbs a color or more of the continuous spectrum, the elements in the atmosphere of a star emits an absorption spectrum rather than a continuous spectrum. Ø A absorption spectrum is produced when light from a hot solid or dense gas passes through a cooler gas (which is the atmospheric gases of the star in this case)

Measuring the chemical composition of a star from its absorption spectrum

Identifying the composition of star’s atmosphere using its absorption spectrum

Composition of a typical star

Ø Here are spectra for some elements common in the atmospheres of stars: • In a star, these elements absorb light at their special frequencies. On the following pages, you will see both the elements for comparison and a star's spectrum. Your job is to identify all the elements you can detect in the star's atmosphere.

Ø Here are spectra for some elements common in the atmospheres of stars: Here is the spectrum of a mystery star: Which elements are present?

Ø Yes, you are correct! Ø The mystery star: Ø has the following elements. Ø Hydrogen Ø Iron

Here are spectra for some elements common in the atmospheres of stars: Here is the spectrum of a mystery star: Which elements are present?

Ø Yes, you are correct! Ø The mystery star: Ø has the following elements. Ø Calcium Ø Hydrogen Ø Magnesium Ø You have identified all the elements

Assignment 1 Ø What is the supernova and how does it differ from the black hole?