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December in Antarctica: The Sun never sets.
The images are 1 hour apart.
The abundances of the chemical elements in the Sun (the cosmic
abundances), relative to106 Si atoms.
Light is a form of electromagnetic radiation and consists of
alternating electric and magnetic fields
The various types of electromagnetic radiation, also referred to as
the electromagnetic spectrum.
Note: The shorter the wavelength of electromagnetic radiation, the higher
is its energy.
The spectrum of visible (“white”) light can be separated into its
various wavelength components with the aid of a glass prism, into
the colors of the rainbow.
Definition: 1 Å (Ångstrom) = 10-8 cm.
Bunsen’s discovery of the characteristic spectral absorption lines of the
chemical elements.
Characteristic spectra of the chemical elements Li, Fe, Ba,
Ca and white light
Determination of the abundances of the chemical elements in the
Sun through the measurement of their spectra with a spectroscope
mounted on a telescope
Spectrum of our Sun, showing the spectral lines of the
multitude of chemical elements present in our star
Spectrum of our Sun, indicating the presence of the spectral
lines of the chemical element Fe
Schematic diagram of the
interior make-up of the Sun.
Listed are the gas density and
the temperature as a function
of depth in the Sun.
Note: density of water = 1,
of rock =~ 3,
and of iron metal = ~ 8.
Relationship between the 3 temperature scales.
In the sciences, the Kelvin scale is commonly used.
Sunspots
appear dark,
because they
are cooler
(~ 4,000°K)
than the
surrounding
photosphere of
the Sun
(~ 5,800°K).
Sunspots occur in pairs
Galileo, the
discoverer of
sunspots
Observation of sunspots on
successive days show the
rotation of the Sun around its
axis.
These observations indicate that
the Sun does not rotate like a
solid body, but has differential
rotation:
Sunspots at Sun’s equator rotate
once around the Sun in ~ 25
days, whereas those at 75° N and
S rotate once around the Sun in
~ 33 days.
Origin of sunspots by compression of magnetic field lines due
to differential rotation of the star.
Sunspots occur in pairs, representing the N and S poles of the
magnetic field lines
The number of sunspots varies from year to year, with an 11
year sunspot cycle.
The 11 year cycle in the frequency of sunspots, observed
continuously back to Galileo
“Granules” in the photosphere of the Sun, 300-1,000 km across. Granules are convection cells,
with hotter gases (~ 200°K) rising in bright centers with velocities of ~ 2 km/sec, and sinking in dark areas.
Solar flare
~ 10 Trillion megawatts
Solar eclipse, showing “solar wind”.
Photographed in 1973 in Kenya.
The “Northern Lights”, or Aurora Borealis