The Electromagnetic Spectrum

1. The Electromagnetic Spectrum

2. Waves • Waves are pure energy. • Waves carry energy from place to place. • Examples of waves are • Heat • Sound • Light • Water

3. Characteristics of Waves • All waves have • Wavelength ( l ) • Amplitude • Speed – how fast a crest travels from one place to another. • Frequency – how many waves pass a point in a unit of time.

4. C = λν • The frequency (v) of a wave is the number of waves to cross a point in 1 second (units are Hertz – cycles/sec or sec-1) • λ is the wavelength- the distance from crest to crest on a wave

5. Electromagnetic Waves The E-M spectrum contains waves that have similar characteristics. These waves do not require a medium and travel at the speed of light. 186,000 miles per hour

6. The Electromagnetic Spectrum

7. Frequency Ranges

8. How is the Electromagnetic Spectrum used in astronomy?

9. Radio Waves • Have the largest wavelengths of all light waves. They can be up to several kilometers long. • Used in Radios, TVs, Communication, and cell phones.

10. Radio Waves and Astronomy • Space objects emit light at many different wavelengths. • Some of the wavelengths are in the radio wave area of the EM spectrum. • Radio waves are collected by radio telescopes and interpreted.

11. Radio Telescopes Parks Radio telescope Very Large Array (VLA) These radio telescopes reflect radio waves into a single focal point where they are collected.

12. What do radio waves show us? • Different astronomical objects emit different lengths of radio waves. • Scientists can study these emissions in order to learn about the makeup and structure of the universe. CO gases in our milky way galaxy as seen by radio waves

13. Microwaves • Have wavelengths that can be measured in centimeters • Used in communication, cooking food, sensing, and imaging.

14. RADAR • An acronym for “radio detection and ranging” • Developed to determine an objects position by firing bursts of microwaves and recording their echo. • Microwaves are able to penetrate haze, clouds, and snow. A radar image from the Space Shuttle.

15. Infrared Radiation • Ranges in size from a single cell to the head of a pin. • Used in imaging, heating food, and remote controls. • Long infrared rays cab be felt as heat, short ones cannot be detected by humans.

16. How do we see with infrared? • Any object that has a temperature radiates infrared radiation (much in the same way very hot objects will emit visible light)

17. Making Infrared Pictures • A special camera is used that is able to detect temperature. Each temperature is assigned a different “false color.” Generally, the warmer an object, the more red or orange it is. The colder, the more blue. This is an image of a cat in infrared.

18. So why use it in Astronomy? • It is easy to study cloud structure. Dark clouds are warmer than light clouds. • We are able to study the effects of urbanization on the earth. What do the red areas represent in this satellite image?

19. Infrared images can tell us things about space such as the concentration of stars and dust. Image of the Milky Way. The hazy, horizontal S-shaped feature that crosses the image is faint heat emitted by dust in the plane of the Solar System

20. Visible Light • The only electromagnetic waves we can see. • Their intensities range from red to violet with violet being the highest in energy.

21. The radiation to which our eyes are most sensitive has a wavelength near the middle of this range, at about 5.5 x 10-7m (550 nm), in the yellow-green region of the spectrum.

22. It is no coincidence that this wavelength falls within the range of wavelengths at which the Sun emits most of its electromagnetic energy—our eyes have evolved to take greatest advantage of the available light.

23. Ultra Violet Radiation • Used in tanning booths, sterilization • Responsible for sun burns and eye cataracts

24. Ultra Violet Light and Astronomy • Hubble Space telescope uses UV light Satellite image of the sun in ultra violet light.

25. The hottest and most active objects in the universe give off UV light. Scientists can learn about these objects by studying the amount of UV light given off. False color image of the earth using UV light. Which side of the Earth is facing the sun? How do you know?

26. Pictures like the one above show which galaxies are new and which ones are old. The top row shows three galaxies in UV light and in visible light in the bottom.

27. X-Rays • Used in x-ray photographs. • Extremely small wavelength. Extremely high frequency and energy. • The earth’s atmosphere is thick enough that x-rays are not able to penetrate to the surface.

28. When the Sun shines on us at a certain angle, our shadow is projected onto the ground. Similarly, when X-ray light shines on us, it goes through our skin, but allows shadows of our bones to be projected onto and captured by film.

29. X-Rays in Astronomy • Astronomers are able to load x-ray detection machines on to satellites. • These satellites are able to detect things like the number of photons collected, the energy of the photons collected, or how fast the photons are detected, can tell us things about the object that is emitting them.

30. Many things in space emit X-rays, among them are black holes, neutron stars, binary star systems, supernova remnants, stars, the Sun, and even some comets! http://chandra.harvard.edu/ The sun in x-ray

31. Gamma Rays • Have the smallest wavelength, highest frequency, and highest energy of any other type of electromagnetic radiation. • Generated by radioactive atoms in nuclear explosions. • Produced in the hottest regions of the universe • Things like supernova explosions (the way massive stars die), neutron stars and pulsars, and black holes are all sources of celestial gamma-rays.

32. How light or electromagnetic radiation is used in Astronomy • Astronomers use a tool called a spectroscope to separate starlight into its colors – in this way, they can tell what a star is made of, its temperature, luminosity and so on… • Astronomers can look at astronomical objects at different wavelengths…

33. Below is a picture of the spectral lines given off by hydrogen. Note there are 3 different frequencies.

34. Atoms and Light • The movement of electrons inside of atoms produces light and other electromagnetic radiation. • Sunlight produces every color in the rainbow but… • Each element gives off only certain frequencies of light, called spectral lines. In effect each element has its own signature of spectral lines allowing us to identify which element we have or what stars are made of.

35. The emission spectra makes it possible to identify inaccessible substances. Most of our knowledge of the universe comes from studying the emission spectra of stars. • Below is the spectra of a few more elements. Helium

36. Neon • Argon

37. In a star, there are many elements present. The way we can tell which are there is to look at the spectrum of the star. • From spectral lines astronomers can determine not only the element, but the temperature and density of that element in the star • Emission lines can also tell us about the magnetic field of the star. The width of the line can tell us how fast the material is moving

38. Spectra of a Star