Our UniverseOur Universe

StarsStars

B lu eH ottes t

Y e llowM ed iu m tem p era tu re

S u n

R edC oo les t

C o lo rs an d Tem p era tu res

Different Types of Stars

A. Giants D. Supergiants

B. White Dwarfs E. Sun

C. Main Sequence

Star ColorStar Color Stars have differentStars have different colors colors Some look red (like Betelgeuse), some Some look red (like Betelgeuse), some

look more yellow (like the Sun), and somelook more yellow (like the Sun), and somelook blue or blue-white (like Sirius)look blue or blue-white (like Sirius)

Color is directly related to temperatureColor is directly related to temperature

Light is not sensitive to the details ofLight is not sensitive to the details of the star's composition but to itsthe star's composition but to its

temperaturetemperature(according to which law?)(according to which law?)

Astronomers can determine:Astronomers can determine: 1.1. the surface temperature of a star by the surface temperature of a star by measuring its color measuring its color

2.2. the composition of its outer layers by the composition of its outer layers by looking at its spectral lineslooking at its spectral lines

Sagittarius Star Cloud, HST

Sun

Star color and brightnessStar color and brightness Is a star’s color Is a star’s color

(temperature) (temperature) related to its size?related to its size?

Is the relation the Is the relation the same for all stars?same for all stars?

Are there different Are there different kinds of stars?kinds of stars?

Electromagnetic RadiationElectromagnetic Radiation

Energy that travels Energy that travels through space in through space in waveswaves

Stars give off Stars give off electromagnetic electromagnetic radiation in different radiation in different formsforms

Each form has its own Each form has its own wavelengthwavelength

Radio WavesRadio Waves Infrared RaysInfrared Rays Visible LightVisible Light Ultraviolet LightUltraviolet Light X-RaysX-Rays Gamma RaysGamma Rays

Continuous spectrum and Continuous spectrum and Absorption spectrumAbsorption spectrum

A Any visible white light consists of A Any visible white light consists of millions of colors, including the seven very millions of colors, including the seven very obvious colors: red – orange – yellow – obvious colors: red – orange – yellow – green – blue – indigo and violet.green – blue – indigo and violet.

A hot glowing object like a wire inside the A hot glowing object like a wire inside the bulb gives off a bulb gives off a continuous spectrumcontinuous spectrum..

A continuous spectrum is a spectrum that A continuous spectrum is a spectrum that shows all colors.shows all colors.

Continuous SpectrumContinuous Spectrum

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

Absorption SpectrumAbsorption Spectrum

Because each element in this world Because each element in this world absorbs a color or more of the continuous absorbs a color or more of the continuous spectrum, the elements in the atmosphere spectrum, the elements in the atmosphere of a star emits an absorption spectrum of a star emits an absorption spectrum rather than a continuous spectrum.rather than a continuous spectrum.

A absorption spectrum is produced when A absorption spectrum is produced when light from a hot solid or dense gas passes light from a hot solid or dense gas passes through a cooler gas (which is the through a cooler gas (which is the atmospheric gases of the star in this case) atmospheric gases of the star in this case)

Measuring the chemical Measuring the chemical composition of a star from its composition of a star from its

absorption spectrumabsorption spectrum

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

Composition of a typical starComposition of a typical star

Here are spectra for some elements Here are spectra for some elements common in the atmospheres of stars: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 Here are spectra for some elements common in the atmospheres of stars:atmospheres of stars:

Here is the spectrum of a mystery star:Which elements are present?

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

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

Assignment 1Assignment 1

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