The Sun

1
The Sun

• Unit 6 Astronomy

2
Firstwe have to discuss light

• Information about universe
• Light emitted from stars and other bodies in
  space
• Electromagnetic spectrum arrangement of waves
  according to their wavelengths and frequencies
• We see visible part of spectrum

3
Visible Light

• A range of waves with various wavelengths
• Passed through a prism
• Violet bent more than blue
• Blue bent more than green
• Etc.

4
Spectroscopy

• Study of the properties of light that depend on
  wavelength
• absorption spectrum visible light is passed
  through a cool gas under low pressure

5
Absorption Spectrum

• Each element or compound in gaseous form produces
  unique set of spectral lines
• Studying a star
• Lines indicate which elements --gt stars chemical
  composition

6
Remember the Doppler Effect?

• Light from a source moving away from you appears
  redder
• Waves are lengthened
• Moving toward you appears bluer
• Waves are shortened
• Determine whether a star or other body in space
  is moving away from or toward Earth
• Measured from the dark lines in spectra and
  comparing them with a standard spectrum

7
Intro to the Sun

• Average star
• Earths primary source of energy
• Only star whose surface we can study
• Diameter 109 Earths
• Mass 332,000 times of Earth

8
Our Sun is a Star
9
Structure of the Sun

• Sun is made of gas
• No clear boundaries between layers
• 4 parts
• Solar interior
• Photosphere
• Chromosphere
• corona

10
Photosphere

• Visible surface
• Radiates most of the sunlight we see
• Layer of gas
• Grainy texture --gt granules
• Composition 90 hydrogen, almost 10 helium
• Dark lines of absorption spectrum

11
Chromosphere

• Above the photosphere
• Thin layer of hot gases
• Can see during a total solar eclipse (red rim)
• Light from photosphere is blocked out

12
Corona

• Outermost portion of the solar atmosphere
• Weak
• Envelope of gases --gt extend a million
  kilometers from sun

13
Corona

• Solar wind streams of protons and electrons
  ejected at high speed from the corona
• Travel through solar system and are lost to space
  
• Alters appearance of bodies in the solar system
• Earths magnetic field doesnt allow them to
  reach our surface --gt do affect our atmosphere

14
Solar Wind
15
Sunspots

• Dark spots on the surface of the sun
• Temperature is less than the surrounding solar
  surface
• Number of sunspots observable vary in an 11-year
  cycle
• Increases to maximum (100) --gt then decrease to
  minimum
• Motion of sunspots --gt sun rotates about once a
  month
• Not all parts rotate at the same speed (gaseous)

16
Sunspots
17
The Solar Cycle
18
Prominences

• Concentration of gases often appearing as arches
  extending beyond corona
• Sometimes can erupt ? matter escapes Suns
  atmosphere

19
Solar Flares

• Sudden eruption
• Above sunspot cluster
• Release lots of energy (UV, radio, X-ray)
• Atomic particles released --gt reach Earth day
  later (affect long-distance radio communications)
• Auroras bright display of light caused by solar
  radiation interacting with the upper atmosphere
  at the poles
• Following strong solar flare

20
How Solar Activity Affects the Earth
21
Solar Interior

• Source of energy nuclear fusion
• Combining of the nuclei of lighter elements to
  form a heavier element
• Energy released because some matter is converted
  to energy

22
Introduction to Nuclear Energy
23
Process of nuclear fusion

• Converts four hydrogen nuclei into the nucleus of
  a helium atom
• Lots of energy released!
• 4 hydrogens 4.032 amu 1 helium 4.003 amu
• Missing mass! (.029 amu)
• Animation

24
Process of nuclear fusion

• E mc2
• c speed of light
• Speed of light is very high (300,000 km/sec) --gt
  amount of energy released from small mass is very
  high
• One pinhead of hydrogen to helium gt burning
  thousands of tons of coal

25
Nuclear Fusion in the Sun

• Small percentage of hydrogen is converted to
  energy
• Helium forms the solar core --gt grows

26
Future of the Sun

• Will the sun run out of hydrogen fuel?
• Last another 100 billion years
• Sun will grow
• Engulf Earth
• Sun can exist in its stable state for 10 billion
  years
• Already 4.5 billion years old