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Lecture

ASTA01H3 Lecture Notes - Positron


Department
Astronomy
Course Code
ASTA01H3
Professor
Lowman

Page:
of 3
Lecture 22: Space Based Astronomy
oInfrared Radiation
oCan image where visible is blocked off
oCan be done on Earth
oUltraviolet observing has to be in space
because ultraviolet is absorbed by atmosphere
oX rays and Gamma Rays do not reflect off
mirrors as other wavelengths
oX ray reflect at shallow angle and can be
focus
oMirrors shaped like sections of cones placed in an arrangement where they
shar a common axis
oGamma rays cannot be focused at all, images appear coarse
Only be done in space
Image created by pointing at one direction for a certain time then
moving slightly and recording then plotting it in map
Lecture 23: The Sun
o1.3 Million earth would fit in the sun
oRotation is differential
oPeriod is about a month
oSurface temperature is 5780K
oSurface visible is called photosphere
o91% hydrogen, 7.8% helium
oSun extends beyond photosphere
oInterior of the sun
oCore is where nuclear fusion takes place
oWe are able to look through the Corona, Transition Zone and Chromosphere
oLuminosity – total energy radiated by the Sun per unit time
oSuns total luminosity = = 10 billion 1 megaton nuclear bombs per second
Solar constant – amount of Sun’s energy reaching Earth is 1400 W/m2
oEvery kg of the Sun produces 0.2 milliwatts of energy
This will continue through 10 billion years producing 3x10^13 J/kg
oNuclear fusion
Nucleus 1 + nucleus 2 nucleus 3 + energy
Mass turned into energy E=mc2
oLike-charged nuclei get close enough to fuse eachother
Only happens in high temperature over 10 million K
Proton + proton deuteron + positron + neutrino
Positron is like electron but positive charge
Neutrino has no charge and very little mass
Positron is anti matter. It is annihilated by collision with an electron
resulting in a gamma ray
Second step is formation of isotope of helium
Final step: 2 helium -3 isotopes forms helium 4 and energy
Gamma rays produced as byproducts of collisions at stage , II, III
Electrons are freed during proton proton collision
Ultimate result is
Helium stays in the core
Gamma rays travel out of core gradually lose energy and emerge as
visible light
Neutrinos escape without interacting
For interaction 4.3x10-12 J is created
Looses 4.3 million tons of matter every second
oSolar interior
Equilibrium, inward gravitational force balanced by outward pressure
High pressure associated with temperature
Core is 20 times more dense than iron yet it is made out of helium
90% of its mass is in 1/8th of its volume
10 000K is required for hydrogen fusion
Radiation zone – transparent
Atoms are ionized and cant absorb radiation
Convection zone – opaque
Many layers
Cooler layers where atoms are not ionized so they can absorb
radiation
Once density of outer parts are too thin then radiation goes
outwards
oSun Spots
Appear dark because they are cooler than surrounding
Temperature of umbra is 4500K and penumbra about 5500K
Come and go and can last up to 100 days
Spots are linked by magnetic field
Sun has a 11 year sunspot cycle
Actually a 22 year cycle because Sun switches polarity every 11
years
Maunder minimum: period of few sunspots
Correlates with little ice Age recorded in Europe and Eastern
North America
Cooler chromospheres is above the photosphere
Annular eclipses where part of the photosphere can be seen
Temperature in the coron are great enough that particles obtain
enough energy to escape the Suns gravitational pull
These particles move outward – solar wind
Solar wind escapes the Sun mostly through coronal holes
oSolar Prominence is large sheet of ejected gas –last days or weeks
oSolar flare- large explosion of sun’s surface – lasts seconds or minutes
Temperature here reach hotter than the Sun;s core
Caused by magnetic field activity