1. Astronomy and the Electromagnetic Spectrum

2. Objectives
Identify the visible and non-visible parts of the electromagnetic spectrum
Compare refracting telescopes and reflecting telescopes
Explain how telescopes for non-visible electromagnetic radiation differ from light telescopes, and why they are typically launched into space

3. The Value of Astronomy Astronomy: the scientific study of the universe
Scientists who study the universe are called astronomers
In the process of observing the universe, astronomers have made exciting discoveries, such as new planets, stars, black holes, and nebulas.
By studying these objects, astronomers have been able to learn more about the origin of Earth and the processes involved in the formation of our solar system.

4. Why Study Astronomy?
Astronomy explains the motions of celestial (stars, planets, etc.) objects in the night sky
Astronomy allows us to determine the origin and structure of galaxies, stars (suns) and planets
Explains how the universe evolved with time
Studies of how stars shine may one day lead to improved or new energy sources on Earth.
Astronomers may also learn how to protect us from potential catastrophes, such as collisions between asteroids and Earth.
Astronomical research is supported by federal agencies, such as the National Science Foundation and NASA. Private foundations and industry also fund research in astronomy

5. Characteristics of the Universe
The Universe is an ever expanding space made up of all matter, including galaxies, which are often found in groups and clusters
Galaxy: a collection of stars/suns, dust, and gas bound together by gravity.
Our galaxy is called….The Milky Way

6. Active Galaxies
Centaurus A

7. Galaxies and Solar Systems
Each star within a galaxy is most likely accompanied by a solar system.
Our solar system includes the sun, Earth, other planets, and many smaller objects such as asteroids and comets.
Can you name the planets which orbit our sun?

8. The Local Universe - Our Sun
A photograph of the Sun
Ultraviolet image of erupting prominence

9. Measuring Distance in Astronomy
Astronomical unit (AU): the average distance between the Earth and the sun; approximately 150 million kilometers (km)
So, 1 AU = 150 million kilometers
To get an idea of how far that is….150,000,000km*(1000m/1km)*(3.3ft/1m)(1mile/5280ft)=???
Astronomers also use the speed of light to measure distance.
Light travels at 300,000,000 m/s. In one year, light travels x 1012 km. This distance is known as a light-year.
ALL TYPES OF LIGHT TRAVEL AT THE SAME SPEED

10. The closet star to Earth (other than our sun. ) is 4
The closet star to Earth (other than our sun!) is 4.2 light-years away.

11. How Do We Observe Objects in Space?
Objects emit Electromagnetic Radiation
Electromagnetic Radiation is energy
Light, radio waves, and X rays are all examples of electromagnetic radiation.
The radiation is composed of traveling waves which oscillate repeatedly move back and forth (oscillate) at fixed frequencies and wavelengths.

12. Observing Space
Electromagnetic Spectrum: all of the wavelengths of electromagnetic radiation. (EMS Video)

13. Visible Electromagnetic Radiation
Though all light travels at the same speed, each color of light has a different wavelength. These colors can be seen when visible light is passed through a prism. Elements in Earth’s atmosphere act as a prism.
The human eye can see only radiation of wavelengths in the visible light range of the spectrum.
Electromagnetic radiation shorter or longer than wavelengths of visible light cannot be seen by humans.
The shortest visible wavelength of light is violet, while the longest is red.

14. Reading check
Which type of electromagnetic radiation can be seen by humans?
The only kind of electromagnetic radiation the human eye can detect is visible light.

15. Invisible Electromagnetic Radiation
Invisible wavelengths include infrared waves, microwaves, radio waves, ultraviolet rays, X rays, and gamma rays, and are detected only by instruments.
Infrared (IR) means “below the red”, and has waves longer than waves of visible light.
Ex. Heat
Ultraviolet (UV) means “beyond the violet” and has wavelengths shorter than waves of visible light.
Ex. Certain light emitted by the sun is UV light, and causes us to tan or burn if exposed too long to the sun’s rays

16. Infrared Radiation
Dust obscures regions of star formation. Certain telescopes can be used to see through the dust.
Anglo-Australian Telescope – Infrared image
Hubble Space Telescope – Optical image of the Orion Nebula

17. Telescopes
The telescope is an instrument which collects electromagnetic radiation concentrates it for better observation.
In 1609, an Italian scientist, Galileo, heard of a device which used two lenses to make distant objects appear closer.
Telescopes which collect only visible light are called optical telescopes.
The two types of optical telescopes are:
refracting telescopes
reflecting telescopes

18. Optical Telescopes Refraction: The bending of light
Refracting Telescope: uses a set of lenses to gather, bend and focus light for magnification
Two problems with refracting telescopes
The lenses focus different colors of light at varied distances which causes distortion.
The lenses are too large which causes images to become distorted.
Reflecting Telescopes: uses a curved mirror to gather, reflect, and focus light for magnification
Unlike refracting telescopes, reflecting telescopes can be made very large without affecting the quality of the image.

19. The diagrams below show reflecting and refracting telescopes.
Optical Telescopes
The diagrams below show reflecting and refracting telescopes.

20. Telescopes for Invisible Electromagnetic Radiation
Scientists have developed telescopes which detect invisible radiation
Many of these can only be used from space because Earth’s atmosphere acts as a shield against many forms of electromagnetic radiation.

21. Space-based Telescopes
In space, Earth’s atmosphere cannot interfere with the telescope’s detection of electromagnetic radiation.
These telescopes detect radio waves, gamma rays, x-rays, or infrared
Telescopes beyond the atmosphere of the Earth send back much more detailed information.
Space-based telescopes include the:
Hubble Space Telescope: collects Infrared, visible, and ultraviolet electromagnetic radiation
Chandra X-ray Observatory
Compton Gamma Ray Observatory
James Webb Space Telescope: will detect infrared radiation after it is launched in 2011