Our Universe

Stars

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

Sagittarius Star Cloud, HST Star Color 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 Light is not sensitive to the details of the star's composition but to its temperature (according to which law?) 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 Wien’s law: T=k/lambda(max) Sun

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

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

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

Continuous Spectrum 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 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. 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

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.

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

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

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

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

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