Download The Sun - TutorPlus

The Sun
General details about the Sun
• Nearest star to Earth at distance of 152,100,000
km (max) to 147,100,000 km (min)
• A second generation star with composition
– 73.4% Hydrogen
– 25% Helium
– 1.6% Heavier Elements (Iron etc..)
• Heavier elements are not produced in big bang but
have been produced in a large red-giant star
Sun Specifications
•
•
•
•
•
•
Mass – 1.99 x 1030 kgm
Volume – 1.3 million times the Earth’s volume
Diameter – 1,392,000 km (109 times Earth diameter)
Surface Temperature – 5,500 Kelvin (mean)
Gravity – 280 ms-2 (about 28 times Earth’s gravity)
Light takes around 8 minutes to reach Earth from the
Sun
Structure of the Sun
Structure of the Sun – Zone 1
• Mostly hot and highly ionised plasma
• Core (Zone 1) - Inner most layer where Nuclear
Fusion reaction of Hydrogen to Helium occurs.
Structure of the Sun – Zones 2 to 3
• Radiative Zone 2 – Electromagnetic energy transmitted slowly through this layer
• Interface Zone – Thin layer that generates Sun’s Magnetic Field
• Convection Zone 3 – Region where energy is transmitted to the surface by
convection currents
• Note: It takes millions of years for the heat to reach the surface !
Atmospheric
structure of the Sun
• The visible surface of
the Sun is called the
Photosphere. It emits
visible light, infra red
and UV radiation
Atmospheric
structure of the Sun
• The lower atmosphere is
called the Chromosphere
which is about 100,000 km
thick.
• The Chromosphere
contains ‘spike like’
prominences, called
spicules, that rise like
geysers carrying magnetic
fields.
Spicules
Solar Prominences
A large looping curtain of gas
Corona
• The Corona is the outer
atmosphere of the Sun.
here radio waves and xrays are emitted. The
Corona can reach
temperatures of 1,000,000
degrees Kelvin.
• The Corona can extend
many millions of
kilometres into space.
Sunspots
• Sunspots are associated
with magnetic storms.
They are regions of intense
magnetic activity.
• They appear as dark spots
because they are cooler
than the surrounding
surface. The temperature of
sunspots is about 3800
Kelvin.
Sunspots – produced by the rotating Sun
stretching the magnetic field lines
Solar flares
• Solar flares are sudden
explosive outbursts of
radiation and matter
near sunspots.
• Both sunspots and solar
flares cause massive
disruption to radio
communications.
Sunspots and
Solar flares
Sun’s Corona
Sunspots
Solar flare
Emissions from the Sun
• Electromagnetic Radiation
– Produces a range of radiations from shortwavelength gamma to long radio.
– However, visible spectrum is most intense
wavelength (peak at 460 nanometres).
– The visible and infra-red closely matches
theoretical radiation curve of ‘black body’ at a
temperature of 6000 Kelvin.
Emissions from the Sun
• Solar Wind & Interplanetary Magnetic Field
– Difference in pressure between corona and
interplanetary space causes outflow of material from
corona. This is the solar wind.
– Speeds of 400–500 kms-1 and takes 3 to 4 days to reach
Earth.
– Near Earth has density of 5 protons and 5 electrons per
cm3.
– Velocity of particles results in temperature of 10,000 to
100,000 Kelvin.
Solar Wind & Interplanetary
Magnetic Field
• In the photosphere a
magnetic ‘coupling’
occurs between magnetic
field belonging to plasma
of solar wind and Sun’s
magnetic field.
• This results in Sun’s
magnetic field lines
becoming locked into the
plasma.
Solar Wind & Interplanetary
Magnetic Field
• The out flowing solar wind
thus carries the magnetic
field lines with it.
• As the Sun rotates it winds
the field lines into a giant
spiral – as shown opposite.
• At the Earth the field lines
are approximately 45
degrees to the direction of
the Sun.
The Solar Cycle
• Sun experiences a cyclic pattern of turbulent
activity (about every 11 years).
• Period of peak activity is solar maximum while
period of least activity is solar minimum.
• The solar cycle is an 11 year cyclical pattern of
increasing and decreasing frequency of:
–
–
–
–
Sunspots
Solar flares
Prominences
Coronal mass ejections
The Sunspot Cycle
• Easiest way to observe the solar activity is to look
at sunspot activity.
• The sunspot cycle is a cyclical pattern of
increasing and decreasing number of sunspots.
• At solar maximum there is usually over 100
sunspots appearing simultaneously on the Sun’s
surface.
• At solar minimum there may be no sunspots.
• The sunspot cycle on average is 11 years (but can
vary between 7 and 13 years).
The cyclic nature of sunspot activity
Radiocarbon levels in tree rings and
sunspot activity !!
Sunspot activity and solar latitude
• Appearance of sunspots changes in solar
latitude during a sunspot cycle. They start at
around 40 degree latitude and end at around
the Sun’s equator.
The Sun-Earth Connection
- Electromagnetic radiation
• The Sun emits a wide
range of electromagnetic
radiation.
• In the Earth’s atmospheric
different wavelengths of
radiation get absorbed by
different molecules.
The Sun-Earth Connection
- The Solar Wind
• The solar wind carrying the interplanetary
magnetic field interacts with the Earth’s magnetic
field.
• Most of the wind flows around and past the Earth
distorting the Earths magnetic field to create a
‘tail’ shape.
• The magnetosphere is the region surrounding a
planet that contains its distorted magnetic field.
The magnetosphere of the Earth
The Van Allen Belts
• The Van Allen Belts are two zones of radiation (ions) that
wrap around the Earth. They are a result of ions from the solar
wind been captured by the Earth’s magnetic field lines.
The Auroras