Lecture 17 The Sun October 31, 2018

Transcription

1 Lecture 17 The Sun October 31,

2 2 Exam 2 Information Bring a #2 pencil! Bring a calculator. No cell phones or tablets allowed! Contents: Free response problems (2 questions, 10 points) True/False (10 questions, 20 points) Multiple Choice (35 questions, 70 points. Two of these require a calculation.)

3 3 Basic Information Mass = 330,000 M Radius=109 R Density=1400 kg/m 3 Spins differentially P = 25 days at equator P = 36 days at poles Closest star to the Earth. Very strong magnetic field

4 4 Composition of the Sun 75% Hydrogen 24% Helium 1% Trace elements How do we know? Spectroscopic measurements Analysis of solar wind Other important solar data comes from: Solar and Heliospheric Observatory (SOHO) Solar Dynamics Observatory (SDO)

5 5 Solar Atmosphere Corona Photosphere Interior Solar Wind Chromosphere

6 6 Photosphere Layer of gas seen from the Earth Temp ~5800 K Granules -- patches of gas experiencing convection Cooler gas sinking Warmer gas rising

7 7 Chromosphere Layer of less dense gas Seen only during solar eclipses or with special filter Light red or pink in color (because of atomic hydrogen) Rising jets of gas = spicules

8 8 Corona Seen only during a solar eclipse Thin, hot gas (over 1 million Kelvin) Why so hot??? Energized by the Sun s complex magnetic field.

9 9 The photosphere of the sun is A. a thin pinkish gas with rising spicules. B. a 5800 K layer with convective granules. C. a hot thin gas energized by the magnetic field. D. a dense, hot layer enriched by helium.

10 10 Solar Wind Outflow of particles from Sun into space Mainly protons and electrons. Sun ejects 1 million tons of mass per second Greatest wind is emitted through coronal holes

11 11 Sunspots Dark, cooler (~ 4300 K) spots on surface of Sun. Powerful magnetic field 5000 stronger than Earth s Lifetime of ~2 rotations (8 weeks). More numerous in an ~11 year cycle.

12 12 Solar Photosphere features This time-lapse movie shows three and a half hours in the life of a sunspot (note the clock at upper right). A sunspot consists of a dark central umbra and a feather-like penumbra. Around them, granules some 1000 km across rise and fall in the hot photosphere. Each granule releases enough energy in its 8-minute lifetime to supply the United States with its energy needs for 300 years. Sunspot groups, which may last for about two months, are produced by cycles in the Sun's magnetic field. To measure the Sun's rotation, observers can track the motion of sunspot groups, much as Galileo did four centuries ago. (This movie shows these motions over a period of about two weeks.) Such studies show that the equatorial regions of the Sun rotate somewhat faster than the polar regions.

13 13 Sunspot photo Close up image of sunspot and granules. Click here for more info on this image

14 14 Mega sunspot of November 2015 So you thought Halloween was over? Think again. There is a monster spot on the Sun. AR2443 has more than quadrupled in size since it first appeared on Oct. 29th, and it now stretches more than 175,000 km from end to end. Philippe Tosi took this picture of the active region on Nov. 1st from his backyard observatory in Nîmes, France. The sunspot has more than a dozen dark cores, many of which are as large as terrestrial continents--and a couple as large as Earth itself. These dimensions make it an easy target for backyard solar telescopes. Of greater interest is the sunspot's potential for explosive activity. The spotty complex has a 'beta-gamma' magnetic field that harbors energy for strong M-class solar flares. Any such explosions will be geoeffective as the sunspot turns squarely toward Earth in the days ahead. (SpaceWeather.com for November 2, 2015)

15 15 Solar Cycle Last solar maximum = 2001 Next: 2012 Currently leaving solar activity minimum

16 16 Solar Activity

17 17 Solar Activity

18 18 Solar Activity

19 19

20 20 Formation of Sunspots Sun rotates faster at the equator than at the poles Magnetic field under surface becomes wound up Magnetic field gets pushed above surface. Magnetic field inhibits warmer gas from moving to those areas where field pushes through surface.

21 21 Sunspots are dark because A. they are cool relative to the gas around them. B. they contain 10 times more iron than the surrounding regions. C. nuclear reactions occur in them at a slower rate than in the surrounding gas. D. they are clouds in the cool corona that block our view of the solar surface. E. absorption lines are clustered together there.

22 22 One major feature that distinguishes a sunspot from other regions on the Sun is A. faster rotation around the Sun's axis than neighboring regions. B. its greater light emission compared to the photosphere. C. its very powerful magnetic field. D. a coronal hole existing above it.

23 23 Prominences and Solar Flares Prominences Hot gas lofted upwards by the magnetic field. Associated with sunspots The least energetic solar atmosphere phenomenon Solar Flares Gas and particles erupt off of the surface Produce sun quakes Associated with sunspot groups

24 24 Prominence -- SOHO

25 25 Sunquake -- SOHO

26 26 Coronal Mass Ejection Gigantic event sometimes set off by flares Can create disruption of satellites, communications, and power grids

27 27 Flares and CME Video Notice the stars drift to the right as the camera follows the Sun, which goes eastward along the ecliptic, about 1 per day. The bright planet is Mercury, the star Spica (Virgo) is below the Sun at the start, and the star Zubenelgenubi (Libra) appears later to cross above Mercury. The SOHO detector array goes crazy when charged particles from a CME strike it. (APOD 10/29/03) (Original NASA file)

28 28 Solar Dynamics Observatory Launched February 11, 2010 Web site: Spectacular 4K video published 11/1/15 Daily information at spaceweather.com

29 30 Jack O Lantern Sun NASA Solar Dynamics Observatory image. Active regions on the sun combined to look something like a jack-o-lantern s face on Oct. 8, The active regions in this image appear brighter because those are areas that emit more light and energy. They are markers of an intense and complex set of magnetic fields hovering in the sun s atmosphere, the corona. This image blends together two sets of extreme ultraviolet wavelengths at 171 Å and 193 Ås, typically colorized in gold and yellow.

30 31 The Energy of the Sun Sun produces energy through the process of nuclear fusion 4 hydrogen atoms are combined to form one helium atom H H p p H H p p n p He n p Energy

31 32 During fusion, some of the mass is transferred into energy through E = Energy 2 E = mc m = mass Fusion can only occur in the core of the Sun high gravitational pressure high temperatures c = speed of light

32 33 Interior Structure of the Sun Core Nuclear fusion produces energy Radiative Zone Energy is transported by photons of light Convective Zone Warmer gas moves upward, cool gas sinks Animation

33 34 Hydrostatic Equilibrium Hydrostatic equilibrium is the balance between pressure of out-flowing energy pushing outward and inward pull of gravity. Keeps the Sun from collapsing due to gravity

34 36 Summary