Transcript The Sun (continued). - Department of Physics and Astronomy

Lecture 36
The Sun.
Tools of Astronomy.
Chapter 17.1  17.7
• The Sun (continued)
• Telescopes and Spacecrafts
Hydrogen Fusion in the Sun
The proton-proton chain
How does the Light Comes Out?
Photons are created in the nuclear fusion cycle.
They collide with other charged particles and
change their direction (random walk).
They also decrease their energy while walking.
It takes ~10 million year to get outside.
The random bouncing occurs in the radiation zone
(from the core to ~70% of the Sun’s radius).
At T<2 million K, the convection zone carries
photons further towards the surface.
The Sun’s Internal Structure
Solar Neutrino
Neutrino is a subatomic particle.
It is a by-product of the solar proton-proton cycle.
It barely interacts with anything.
Counts of neutrino coming from the Sun are
crucial to test our knowledge about solar physics.
Neutrino observatories use huge amounts of
different substances to detect nuclear reactions
with neutrino.
So far theory predicts more neutrino than is seen.
The Super Kamiokande Experiment
Information
Sonic Boom
Observations of Solar Neutrino
The GALLEX detector
Gran Sasso, Italy
The Sudbury Observatory
Ontario, Canada
Sunspots and Other Solar Activity
Sunspots have T~4,000 K, cooler than the 5,800 K
surrounding plasma.
Sunspots are kept together by strong magnetic fields.
Usually sunspot appear in pairs connected by a loop
of magnetic field lines.
The loops rising into the chromosphere or corona
may appear as solar prominences.
Solar flares are events releasing a lot of energy
where magnetic field lines break.
Sunspot Close-Up
The Sunspot Cycle
Observations of the Sun since the beginning of
the telescopic era revealed that the number of
sunspots gradually rises and declines.
An average period is 11 years (from 7 to 15 years).
The magnetic fields in sunspots reverse their
direction when a cycle is over.
No sunspots were observed in 16451715, when a
Little Ice Age took place in Europe and America.
The Sunspot Cycle
Summary of the Sun
The Sun shines with energy generated by fusion of
hydrogen into helium in its core.
Gravitational equilibrium determines the Sun’s
interior structure and maintains a steady nuclear
burning rate.
The Sun is the only star near enough to study it in
great detail.
Collecting Light with Telescopes
Telescopes are giant eyes, collecting more light
than we could with our naked eyes
Telescopes are characterized by 2 key properties
Light-collecting area (depends on the telescope
size)
Angular resolution (how much detail we can see in
the telescope’s images)
Telescope Design
Two basic designs: Refracting and Reflecting
telescopes
Refracting telescope uses transparent glass lenses
to focus the light
(from Galileo’s small telescopes to a 1-m
refractor)
Refractors
Refractors
Telescope Design
Reflecting telescopes use precisely curved
mirrors
Most contemporary telescopes are reflectors
Primary mirror gather and focuses the light
Secondary mirror reflects the light to a
convenient location
Reflectors
Reflectors
Uses of Telescopes
Imaging - pictures of celestial objects
Spectroscopy - dispersing light into a spectrum
Timing - tracking time variations of the light
Atmosphere affects observations - light
pollution, turbulence
Turbulence can be corrected by adaptive optics
Types of Telescopes
Optical and Infrared telescopes
Radio telescopes (use metal “mirrors”)
Interferometeres (link several separate telescopes
together to improve angular resolution)
Observatories
Radiotelescopes
Satellites
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First satellite  1957 Soviet Sputnik
First astronomical satellites  late 1960’s
The Hubble Space Telescope (HST)  1990
The X-ray Chandra Observatory  1999
The Spitzer Space (IR) Observatory  2003
Satellites