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Unit 4: Our Sun

Unit 4: Our Sun. Part 1: Our Sun. Getting to Know Our Sun. Dominant object in sky Source of light and heat Studied using ground-based telescopes, observations during eclipses, spacecraft, and spectrometers A work in progress…. Meet Our Sun. A Big Boy.

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Unit 4: Our Sun

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  1. Unit 4: Our Sun Part 1: Our Sun

  2. Getting to Know Our Sun • Dominant object in sky • Source of light and heat • Studied using ground-based telescopes, observations during eclipses, spacecraft, and spectrometers • A work in progress….

  3. Meet Our Sun

  4. A Big Boy • Diameter = 1.4 million km (110 Earths, and a million Earths could fit inside!) • Mass = 2 × 1030 kg (300,000 Earths) • Density = 1.4 g/cm3 • Temperature = Varied, but hot (duh)

  5. But A Rather Average Star… • Not the hottest, but not the coldest • Not the biggest, but not the smallest • Not the blue-est, but not the red-est (Note to self: Play the Sun Song Here)

  6. Like Onions and Ogres

  7. Our Sun Part 1: The Outer Layers

  8. Photosphere • The “Sphere of Light” • Lowest level of sun’s “atmosphere” • Part of the sun that we see (comparable to Earth’s crust) • ~ 500 km thick • Temperature: ~ 5 800 K (10,000oF)

  9. Like Onions and Ogres

  10. A Busy Place, the Photosphere Granulations ~700 km in diameter Oscillate up and down over several minutes

  11. Chromosphere • “Sphere of Color” • ~ 10,000 km thick (1.5% of sun’s radius, same proportion as Earth’s atmosphere) • Temperature: 7,000 K – 15,000 K

  12. Like Onions and Ogres

  13. Also an Active Place • Spicules: • Jets of gas rising from surface like “blades of grass” • ~700 km across and 7,000 km tall • Each lasts about 5-15 minutes • ~ Half a million on sun at any giventime

  14. Corona • The “Crown” • Outer layer, technically extends throughout solar system (aka – the “solar wind”) • Particles in solar wind take 20 days to reach Earth • Mainly plasma (gas particles with a charge) • Very diffuse: 1 billionth the pressure of Earth’s atmosphere

  15. Like Onions and Ogres

  16. Streamers Corona Visible only in Solar Eclipse

  17. Our Sun Part 2: Solar Activity (on the outside)

  18. A Busy Boy Visible Solar Activity: • Sunspots • Solar Flares • Prominences

  19. 1. Sunspots

  20. Acne of the Solar World • First “discovered” and studied by Galileo (and other) in 1610 • Previously had been observed with naked eye • Dark spot on sun: less light emitted, therefore cooler • But still bright: Sunspots are as bright as a full moon • Very large: about Earth-size

  21. A Sunspot Close Up Umbra “shadow” Penumbra

  22. What is a Sunspot? • Area of very strong magnetic field (1,000 times that of Earth) • Alters flow of plasma in sun’s photosphere, causing “cool” spots • Other than that, no one really knows…

  23. A Regular Thing • Sunspot activity runs in 11-year cycles (corresponding to 11 year cycle of sun’s magnetic field flipping) • Maximum number of sunspots every 11 years • Currently in a lull. Bummer.

  24. Sunspot Activity

  25. A Transient Thing Sunspots usually last several weeks or even months

  26. Effects of Solar Activity • Solar wind can disrupt radio and TV signals and even the electricity grid • Northern Lights • Affects weather? (Even though sun’s output changes only 0.2%) • Space Weather: www.spaceweather.com

  27. A Coincidence? From 1645-1715 there were very few sunspots, even during the maxima. This is known as the Maunder Minimum, and represents a period of solar inactvity that coincides with the 'Little Ice Age' on Earth.

  28. 2. Solar Flares • Huge eruptions/storms near sunspots • Last up to 4 hours • Very hot and very light intensive • UV and x-rays can mess up radio and TV reception on Earth • Slower-moving particles later give aurora and possibly cause power line blackouts • Energy of up to 40 billion atomic bombs!

  29. And You Thought the Sun was Bright? Try a Solar Flare.

  30. 3. Solar Prominences • Giant “loops” hanging off the sun • Can last for weeks, months, or just moments

  31. More Solar Prominences

  32. Our Sun Part 3: A Peek Inside

  33. How a Star is Born A star begins as a huge cloud of gas (mainly hydrogen and helium) in space: H and He Gas

  34. Star Nurseries - Nebulae The giant clouds of dust and gas where stars are formed are often called nebulae (nebula, singular). They are quite beautiful…

  35. Orion Nebula

  36. Horsehead Nebula

  37. Trifid Nebula

  38. Keyhole Nebula

  39. Eagle Nebula

  40. The Pillars of Creation

  41. Ever felt like your whole cloud is falling in on you? Gravity causes the cloud to collapse inward, increasing the density, temperature, and pressure within the cloud:

  42. This Little Light o’ Mine… Once the temperature and pressure inside the cloud become great enough, fusion begins and the star ignites!

  43. A Hunk of Burnin’ Love A star begins its life by fusing hydrogen (its most abundant element) into helium: 4 1H → 4He + νe + ENERGY (light, heat, etc.) (νe is a tiny subatomic particle known as a neutrino) This constant output of energy and radiation from the star’s center keeps the star from collapsing under its own weight.

  44. A Balancing Act Gravity pulls the star inwards, making it collapse. BUT Fusion! Light and heat produced by fusion in the core push the sun outward, making it expand. Eventually an equilibrium is reached and the star maintains a stable size.

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