The Sun Astronomy 311 Professor Lee Carkner Lecture 23.
-
date post
19-Dec-2015 -
Category
Documents
-
view
220 -
download
1
Transcript of The Sun Astronomy 311 Professor Lee Carkner Lecture 23.
WARNING !
NEVER LOOK DIRECTLY AT THE SUN
NEVER LOOK AT THE SUN WITH BINOCULARS OR A TELESCOPE
PERMANENT EYE DAMAGE CAN RESULT
Observing the Sun
With a solar filter in place we can use a telescope to get a high spatial resolution optical image of the Sun
The Sun From the Inside Out
We will examine the Sun from the core to the diffuse outer layers
Nuclear fusion and magnetic fields play key roles in the energetics and structure of the Sun
Why Does the Sun Shine?
From radioisotope dating we know that the solar system is 4.5 billion years old
What could power the Sun for this length of time?
The Core At the core of the Sun the temperature
and pressure are very high due to the weight of the outer layers
At these conditions the hydrogen atoms are moving so fast and are packed together so tightly that they can fuse together to make helium:
How Does the Energy at the Core Get Out?
In general energy is transported in 3 ways: Conduction -- Radiation -- Convection --
Radiative and Convective Zones Radiative Zone (0.25-0.71 Rsun)
Convective Zone (0.71-1.00 Rsun) Hot material rises causing convection
The Photosphere It takes about 170,000 years for the energy to
reach the surface of the Sun
The photosphere has an average temperature of 5800 K The top layer will absorb some of the light from the
bottom layers producing absorption lines
Granulation in the Photosphere
The photosphere is at the top of the convective zone
The photosphere is covered with
granules (each about 1000 km across)
Sunspots in the Photosphere
The photosphere sometimes has small dark regions called sunspots
Sunspots are regions where the
Sun’s magnetic field inhibits the flow of warmer material
Sunspot Cycles Sunspots exist for a maximum of a few
months There is a sunspot cycle of 11 years
The sunspots move towards the equator over the course of the cycle
Sunspot Cycles and Differential Rotation
The Sun rotates differentially
The magnetic field gets “wrapped-up” around the equator
The sunspots are caused by the magnetic field “kinks”
The Sun’s Magnetic Field
The Sun’s magnetic field extends far out beyond the surface
These loops can break and reconnect
The Chromosphere
The chromosphere is a diffuse layer of the solar atmosphere extending from the photosphere to about 2000 km
It has a temperature of about 20000 K
The Structure of the Chromosphere
The chromosphere is composed of many rising filaments of hot gas called spicules
Between the chromosphere and the corona is the transition region where the temperature rises from 20,000 K to 1 million K over a small region
The Corona The corona is the outer layer of the Sun’s
atmosphere
It is thinner and hotter than the chromosphere
The high temperatures produce a hot ionized gas called a plasma
Flares and Magnetic Activity
The material in the corona is constantly changing
Flare activity is linked to sunspot
activity
Changes in magnetic activity seem to effect climate
The Structure of the Corona The high temperatures and
irregular structure of the corona are due to magnetic fields
The tangled, shifting magnetic loops gives the corona its structure
Summary: Structure of the Sun
Core fusion converts H to
He and power the Sun
Radiative Layer transports energy
from the core
Convective Layer transports energy
to the photosphere
Photosphere visible surface of
the Sun
Chromosphere hot middle
atmospheric layer
Corona very hot outer
layer
Summary: Solar Energetics
Thermonuclear Fusion Energy is produced at the core of the Sun by
converting hydrogen to helium Energy Transport
Energy is transported via radiation where the opacity is low and via convection where the opacity is high
Magnetic Fields The outer layers of the Sun are composed of
hot plasma in magnetic loops