Fusion Reactions in the Sun
The Electromagnetic Spectrum
The Sun is a Magnet The field is dragged by the rotation, and flips polarity every 11 years
A Solar Prominence
The Solar Wind
Charged particles spiral into Earth’s magnetic field; collide with atmospheric atoms and excite electrons into higher energy levels; when the electrons return to ground state, they emit visible light
The Aurora Borealis (Northern Lights)
As helium builds up in core, star expands in size
Outer layers are eventually blown off to become a planetary nebula
The Future of Our Sun
What about larger stars than our Sun? There are larger stars than our Sun? Yes In heavier stars, gravity causes the core to get hot enough to cause other reactions:
Elements keep fusing until they get to iron Iron is the fusion “dead end”
Once reactions stop, outward pressure quickly drops to zero
Once reactions stop, outward pressure quickly drops to zero Gravity quickly causes the star to collapse inward Rebound pressure causes the star to explode Supernova!
Stars of about 7-10 solar masses have cores that form neutron stars
Stars of more than 10 solar masses have cores that form black holes
Type I Supernova Occur in multiple-star systems One star is a white dwarf that draws matter from other star When mass of white dwarf is 1.4 times the mass of our Sun (the Chandrasekhar Limit), it supernovas Always has same magnitude (brightness), so can be used to measure distance
Black-body Radiators
Wien’s Law: λpeak T = 2.898 x 10-3 m K
The Hertzsprung- Russell Diagram Annie Jump Cannon (1863-1941)
The Hertzsprung-Russell Diagram