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Ch. 24: “Studying the Sun”
24.1: “The Study of Light”
Electromagnetic Radiation
• Electromagnetic radiation
includes gamma rays, Xrays, ultraviolet light,
visible light, infrared
radiation, microwaves,
and radio waves.
• The electromagnetic
spectrum is the
arrangement of waves
according to their
wavelengths and
frequencies.
2
Electromagnetic Radiation
• Nature of Light
– In some instances, light behaves like
waves, and in others like particles.
– In the light sense, waves can be
thought of like swells in the ocean.
– This motion is characterized by a
property known as wavelength, which is
the distance from one crest to the next.
• Photons
– This is a small packet of light energy.
– Photons from the sun are responsible
for pushing material away from a comet
to produce its tail.
– Each photon has a specific amount of
energy.
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Spectroscopy
• This is the study of
the properties of light
that depend on
wavelength.
• A continuous
spectrum is an
uninterrupted band of
light emitted by an
incandescent solid,
liquid, or gas under
pressure.
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Spectroscopy
• Absorption Spectrum
– This is a continuous
spectrum produced when
white light passes through
a relatively cool gas under
low pressure.
– The gas absorbs selected
wavelengths of light, and
the spectrum looks like it
has dark lines
superimposed.
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Spectroscopy
• Emission Spectrum
– This is a series of bright
lines of particular
wavelengths produced by
a hot gas under low
pressure.
– When the spectrum of a
star is studied, the
spectral lines act as
“fingerprints.”
• These lines identify the
elements present and thus
the star’s chemical
composition.
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The Doppler Effect
• This is the apparent
change in frequency of
electromagnetic or sound
waves caused by the
relative motions of the
source and the observer.
• In astronomy, the Doppler
Effect is used to
determine whether a star
or other body in space is
moving away from or
toward Earth.
– Larger doppler shifts
indicate higher speeds;
smaller Doppler shifts
indicated lower speeds.
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