The Sun. SESAME Astronomy Week 4. Thursday, February 10, 2011

Transcription

1 The Sun SESAME Astronomy Week 4 1 1

2 Our star Not special: typical mass, typical temperature, typical size, typical planetary system about halfway through its 10 billion year lifespan 2 2

3 Vital statistics Radius: 7 x 10 5 km = R Mass: 2 x kg = 1 M 109 R 332,000 M Luminosity: 3 x Watts = 1 L Temperature: 5800* K (surface) day 25 earth days at equator, 33 earth days at poles surface gravity: 28 times stronger than Earth s * Depending on which source you choose, you will find a range of values from

4 a little info about light light is a wave 4 4

5 a little info about light light is a wave 4 4

6 a little info about light light is a wave 4 4

7 blackbody radiation a hot object glows the hotter the object, the brighter it glows the hotter the object, the bluer it glows 5 5

8 blackbody radiation a hot object glows the hotter the object, the brighter it glows the hotter the object, the bluer it glows 5 5

9 blackbody radiation a hot object glows the hotter the object, the brighter it glows the hotter the object, the bluer it glows 5 5

10 blackbody radiation a hot object glows the hotter the object, the brighter it glows the hotter the object, the bluer it glows 5 5

11 Structure core - where the fusion takes place not really differentiated like the planets (although core is slowly going from mostly Hydrogen to mostly Helium) 6 6

12 7 7

13 fusion proton-proton chain (pp chain) 2 protons get close if one happens to turn into a neutron at the moment they are close, the neutron and other proton stick together forming Deuterium (when proton turns into neutron, it emits a positron) Deuterium gets hit by another proton forming Helium-3 and emitting energy 2 Helium-3 nuclei collide forming a Helium-4 nucleus and emitting 2 protons 8 8

14 convection heat from bottom makes material just above it expand and rise this material leaves empty space that is filled from the sides this material leaves empty space that is filled from above heated material cools when it reaches the top previously heated material is pushed aside by rising newly heated material from below previously heated, now cooled material that has been pushed aside sinks back to bottom and the whole thing starts again

15 convection it happens in the sun result is called granules 10 10

16 Sun s magnetic field rotating faster at equator than at poles magnetic field gets pulled along with charged particles field gets tangled up and pops out in places 11 11

17 prominence - where the magnetic field sticks out of surface of sun charged particles spiral around field lines 12 12

18 flare - when the field lines break particles that had been trapped are released into space at high speeds sometimes flare is in direction of Earth 13 13

19 Sunspots magnetic field prevents hot gas from rising to surface where it sticks out of surface places where hot gas can t rise to surface cool off a little (still VERY hot) sunspots only look dark compared to even brighter surface of sun always come in pairs (why?) 14 14

20 sunspots 15 15

21 sunspot cycle know WHAT happens but not WHY every 11 or so magnetic field of sun flips just after a flip, few sunspots, sunspots at middle latitudes at solar maximum, lots of spots and close to equator, lots of prominences and flares* then field flips and sunspots few and at middle latitudes * we ll talk about flares on a later slide from 7-15, average is 11 years 16

22 The sunspot cycle 17 17

23 solar maximum solar minimum more sunspots more prominences more flares fewer sunspots fewer prominences fewer flares 18 18

24 number of sunspots varies from cycle to cycle 19 19

25 20 20

26 How does the energy get out? random walk - photons (the packets of energy released during fusion) bounce around bumping into atoms and nuclei for 30,000-1,000,000* years until they finally wander out 21 * depends on who you ask and what assumptions he/she made 21

27 Summary the sun is an average star the sun is about halfway through its life light is a wave objects glow when they re hot, and how bright and what color depends on temperature: hotter = brighter and bluer, cooler = dimmer and redder Sun converts Hydrogen to Helium in its core (and only in its core) via the proton-proton chain (fusion) light takes up to a million years to make its way from the core to the surface 22 fun fact: Helium was first discovered in the sun magnetic field: sun s magnetic field gets tangled up and flips every 11 or so years magnetic field sticks out of surface (in prominences) and causes prominences and cooler places called sunspots flares happen when field lines in a prominence breaks sunspots always come in pairs only look dark compared to surrounding surface, really they re pretty bright in their own right (brighter than some kinds of stars) 22