Lecture 36The Sun.

Tools of Astronomy.

• The Sun (continued)• Telescopes and Spacecrafts

Chapter 17.1 17.7

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 Sudbury ObservatoryOntario, Canada

The GALLEX detectorGran Sasso, Italy

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 16451715, 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 DesignReflecting telescopes use precisely curved mirrorsMost contemporary telescopes are reflectors

Primary mirror gather and focuses the lightSecondary 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, turbulenceTurbulence 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

• 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