Astronomy and the Electromagnetic Spectrum

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

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 In the process of observing the universe, astronomers have made exciting discoveries, such as new planets, stars, black holes, and exciting discoveries, such as new planets, stars, black holes, and nebulas. 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.

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

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

Active Galaxies

Centaurus ACentaurus A

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?

The Local Universe - Our Sun

A photograph of the SunA photograph of the SunUltraviolet image of Ultraviolet image of

erupting prominenceerupting prominence

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 9.4607 x 1012 km. This distance is known as a light-year.

• ALL TYPES OF LIGHT TRAVEL AT THE SAME SPEED

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

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.

Observing Space

• Electromagnetic Spectrum: all of the wavelengths of

electromagnetic radiation. (EMS Video)

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.

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.

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

Infrared Radiation• Dust obscures regions of star formation. Certain telescopes can

be used to see through the dust.

Hubble Space Telescope – Hubble Space Telescope – Optical image of the Orion NebulaOptical image of the Orion Nebula

Anglo-Australian Telescope – Anglo-Australian Telescope –

Infrared imageInfrared image

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

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

1. The lenses focus different colors of light at varied distances which causes distortion.

1. 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.

Optical TelescopesThe diagrams below show reflecting and refracting

telescopes.

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.

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