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Chapter 24
Studying the Sun
Electromagnetic radiation includes gamma rays, Xrays, ultraviolet light, visible light, infrared radiation,
microwaves, and radio waves
Electromagnetic Spectrum – the arrangement of
electromagnetic radiation according to wavelength
The Light Spectrum
Spectroscopy – the study of the properties
of light that depend on wavelength
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
Solar Spectrum
Doppler Effect – the apparent change in
frequency of electromagnetic or sound waves
caused by the relative motions of the source
and the observer
Red Shift/Blue Shift
In astronomy, the Doppler effect is used to
determine whether a star or other body in space
is moving away from or toward Earth
Refracting Telescope – a telescope that
uses a lens to bend and concentrate the
light from distant objects
Reflecting Telescope
– a telescope that
concentrates light from
distant objects by using
a concave mirror
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
Radio Telescope – a
telescope designed to
make observations in
radio wavelengths
A radio telescope
focuses the incoming
radio waves on an
antenna, which
absorbs and transmits
these waves to an
amplifier, just like a
radio antenna
Space telescopes orbit above Earth’s
atmosphere and thus produce clearer
images than Earth-based telescopes
Hubble Space Telescope
Sun Facts
An “Average” Star
Diameter = 109 x Earth
Volume = 1.25 x Earth
Mass = 332,000 x Earth
Density = ¼ x Earth
We can divide the sun into four parts: the
solar interior; the visible surface, or
photosphere; and two atmospheric layers,
the chromosphere and corona
Photosphere – radiates most of the light we
see and can be thought of as the visible
“surface” of the sun
Chromosphere – A relatively thin layer of
hot gases a few km thick above the
photosphere
Corona – outer most portion of the solar
atmosphere, very weak and is visible only
when the photosphere is covered
Solar Wind – Streams of protons and
electrons that boil from the corona
Sunspots – dark regions on the surface of the
photosphere, an individual spot contains a black
center rimmed by a lighter region
Sunspots appear dark because of their
temperature, about 1500 K less than that of the
surrounding solar surface
Prominences are ionized gases trapped by
magnetic fields that extend from regions of
intense solar activity
Solar Flares – brief
outbursts that normally
last about an hour and
appear as a sudden
brightening of the
region above a sunspot
cluster
During their existence,
solar flares release
enormous amounts of
energy, much of it in the
form of ultraviolet,
radio, and x-ray
radiation
Auroras – following solar flares, Earth’s
upper atmosphere near the magnetic
poles is set alight; also called the northern
and southern lights
Nuclear Fusion – The process by which the sun
produces energy; this nuclear reaction converts four
hydrogen nuclei into the nucleus of a helium atom and
tremendous energy is released
It is believed that a star our size can exist in its stable
state for ~10 Billion years, making our sun middleaged at ~4.5 Billion years old