24.1 The Study of Light

Electromagnetic Radiation

Includes gamma rays, X-rays, UV light, visible light, infrared radiation, microwaves, & radio waves

Electromagnetic Spectrum

Classifies radiation according to wavelength & frequency

Photons – small packet of light energy

Copy diagram on pg. 674 fig. 1

Spectroscopy The study of the properties of light that depend on

wavelength

Continuous spectrum – produced by an incandescent solid, liquid, or gas under high pressure (emit when hot)

Absorption spectrum – produced when visible light is passed through a relatively cool gas under low pressure. (gas absorbs selected wavelengths of light)

Emission Spectrum – produced by a hot gas under low pressure (bright lines)

When the spectrum of a star is studied, the spectral lines act as “fingerprints”

The Doppler Effect Occurs for both sound and light

Change in wavelength of a wave that is emitted from a source that is moving away or toward an object

Light source that is moving away = redder

Light source that is moving toward = blue

Doppler Effect is used to determine whether a star or other body in space is moving away from or toward Earth

REVIEW REVIEW REVIEW

What types of radiation make up the electromagnetic spectrum?

Compare the 3 types of spectra

How are the elements in a star determined?

How can the Doppler Effect tell detection?

24.2 Tools for Studying Space

Refracting Telescopes

Bend or refract light

Objective lens produces an image by bending light from a distant object so that the light converges at an area called the focus (central pt.)

Chromatic aberration ( color & to go astray)

Property of a lens whereby light of diff. colors is focused at diff. places (produces a halo around it)

Blue light is in focus = reddish halo Red light is in focus = bluish halo

https://www.youtube.com/watch?v=VzSjqNE2AHM

Reflecting Telescopes

Chromatic aberration is avoided

Use a concave mirror that focuses light in front of a mirror rather than behind

Most large optical telescopes are reflectors

Light does not pass through a mirror so the glass for a reflecting telescope does not have to be of optical quality

https://www.youtube.com/watch?v=ic2aPxePlEs

Properties of Optical Telescopes

Both refracting & reflecting telescopes have 3 properties that help astronomers

Light gathering power Resolving power Magnifying power

Detecting Invisible Radiation

Radio telescopes – focuses the incoming radio waves on an antenna which absorbs & transmits these waves to an amplifier just like a radio antenna

Poor resolution (-)

Less affected by turbulence than optical telescopes (+)

Radio telescopes are hindered by human made radio interference (hidden in valleys to block these types of interference)

Space Telescopes

Orbit above Earth’s atmosphere & produce clearer images than Earth-based telescopes

Hubble Space Telescope

1st space telescope built by NASA

REVIEW

How does a refracting telescope work?

Compare and contrast a refracting telescope and a reflecting telescope

How do radio telescopes gather data?

Why do space telescopes obtain clearer images than Earth based telescopes?