Electromagnetic Spectrum

Astronomy Chapter 3.1Pages 94, 95, 99 & 100

• Travel in the form of waves

• These waves can travel through empty space.

Electromagnetic Radiation

• ER waves travel at the speed of light– 300,000km per second

• Wavelength, the length from one wave to another, determines the type of radiation

Electromagnetic Spectrum

D. Gamma Rays

B. Visible

C. Ultraviolet

A. Radio Waves

Which of the following has the longest wavelength?

• Emits electromagnetic radiation of all types.

The Sun

Electromagnetic Spectrum• The various types of ER waves arranged on a continuum

• A form of electromagnetic radiation (EMR) that you can see

• A form of energy that travels in waves like:• Radio waves• X-rays• Visible light

What is Visible Light?

• Visible Light– Made of various colors, each with a different

wavelength

– These are the colors seen in a rainbow.

Spectrum

F. Violet

C. Yellow

D. Green

A. Red

Which color has the shortest wavelength?

B. Orange

E. Blue

–When white light is passed through a prism, the light is bent into the visible spectrum.

Spectrum (Prisms)

R – O – Y – G – B – I – V• (Red, Orange, Yellow, Green, Blue,

Indigo, Violet)

Spectrum

Spectroscope• Uses a prism to split the light gathered by a telescope into a spectrum.

• Three different typesContinuous Spectrum

Emission Spectrum

Absorption Spectrum

Three types of Spectra

• Unbroken band of colors

• Shows that the source is emitting all visible wavelengths.

Continuous Spectrum

• A series of unevenly spaced lines of different colors and brightness.

• The bright lines show that the source is emitting light of certain wavelengths.

Emissions Spectrum

• Produced by glowing gases

• Every element has a unique emission spectrum– Allows scientists to determine the elements in

objects.

Emissions Spectrum

• A continuous spectrum crossed by dark lines

• Lines form when light from a glowing object passes through a cooler gas.– The gas absorbs the wavelengths that are

missing.

Absorption Spectrum

• The colors absorbed are the same that the gas would emit– Absorption Spectrum for Hydrogen

– Emission Spectrum for Hydrogen

Absorption Spectrum

D. Absorption Spectrum

B. Emission Spectrum

C. Continuous Spectrum

A. Visible

Which spectrum would you expect to see produced by

glowing gasses?

Which spectrum would you expect to see if you were studying the

gasses on another planet?

D. Absorption Spectrum

B. Emission Spectrum

C. Continuous Spectrum

A. Visible

How do these spectrum allow astronomers to figure out what elements make up the atmospheres of stars and planets?

Absorption Spectrum

• Chemical elements in a star’s atmosphere absorb light from the star.

• Each element absorbs a different wavelength. Each absorbed wavelength is shown as a dark line on a spectrum.

Chemical Composition

• It acts like a finger print each element has a unique set of lines.

• By comparing the star’s spectrum to the known spectrums of different elements, astronomers can determine the elements present.

Chemical Composition

• Most stars have a chemical composition similar to the sun. 73% H, 25%He and 2% other elements.

• Stars at different temps produce different line spectrums.

• If the star is at about 10,000˚C it produces a very strong spectral lines for H.

• If the hydrogen line is not strong, it means the star is cooler than 10,000˚C

Temperatures

Hydrogen

Helium

Sodium

Calcium

Star A

Absorption Spectrums

Hydrogen

Helium

Sodium

Calcium

Star B

Absorption Spectrums

Hydrogen

Helium

Sodium

Calcium

Star C

Absorption Spectrums

Constellations• Patterns of stars in the sky• ORION- The Hunter