SUN - A typical star

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1 SUBMITTED BY-- SUBMITTED BY-- Anamika Nath Anamika Nath B.E. 3rd Semester B.E. 3rd Semester G.U. Roll Number: N-10/48 G.U. Roll Number: N-10/48 Regn. Number: 67864 / 2010-11 Regn. Number: 67864 / 2010-11 Computer Science & Computer Science & Engineering Engineering NITS MIRZA NITS MIRZA

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By- Anamika Nath. B.E. (CSE) - 3rd Semester. NITS Mirza, Assam. Date: 03/12/'11.

Transcript of SUN - A typical star

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SUBMITTED BY--SUBMITTED BY--Anamika NathAnamika Nath

B.E. 3rd SemesterB.E. 3rd SemesterG.U. Roll Number: N-10/48G.U. Roll Number: N-10/48

Regn. Number: 67864 / Regn. Number: 67864 / 2010-112010-11

Computer Science & Computer Science & EngineeringEngineering

NITS NITS MIRZA MIRZA

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Basic Facts:Basic Facts:Age = 4.6 billion years

Orbital Speed = 220 km/s

Mass = 2x1030 kg

Radius = 7x108 m = 7x105 km

Distance = 1.5x1011 m = 1.5x108 km = 8.3 light-minutes

Core temperature : 15 million °C

Average surface temperature: 5,500 °C

Luminosity = 3.9x1026 W (Solar Constant = 1350 W/m2)

Mean Density = Mass/Volume = M/((4/3)R3)= 1400 kg/m3 = 1.4 g/cm32

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Element Abundance(percentage of totalnumber of atoms)

Abundance(percentage of totalmass)

Hydrogen 91.2 71.0

Helium 8.7 27.1

Oxygen 0.078 0.97

Carbon 0.043 0.40

Nitrogen 0.0088 0.096

Silicon 0.0045 0.099

Magnesium 0.0038 0.076

Neon 0.0035 0.058

Iron 0.0030 0.14

Sulphur 0.0015 0.0403

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Anatomy of Anatomy of Sun:Sun:

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Major Major Regions:Regions:

Interior (“Inner-sphere”)

•Core

•Envelope (Radioactive Zone, Convective Zone)

•Atmosphere(“Outer- sphere”)

•Photosphere:Teffctive ~ 5780 K

•Chromosphere

•Corona

No real “surface” - it is gaseous all the way to the center!5

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Temperature rises to ~ 500,000 - 1,000,000 K

Highly ionized atoms, such as Fe+13 (also called Fe XIV)

light scattered by ions & electrons (inner) & dust grains (outer)

Heated by complex magnetic/particle activity

CoronaCorona

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•Sunspots are the dark regions that appear on the surface of Sun.•The amount of solar activity on the Sun is not constant, and is closely related to the typical number of sunspots that are visible.•The number of sunspots and the levels of solar activity vary with an 11 year period known as the solar cycle.

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Solar Cycle:Solar Cycle:Number of spots = ~ 11 yrs

Magnetic polarity of spots = 22 years (to return to starting orientation)

Horace Babcock - Magnetic Dynamo via differential rotation

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Solar Solar Flares:Flares:The most violent events on the surface of the Sun are sudden eruptions called solar flares. Flares typically last a few minutes and can release energies equivalent to millions of hydrogen bombs.

Figure showing multiple solar flaresFigure showing multiple solar flares

It’s the sudden release of energy equal to 100s of millions of megatons - radio through gamma rays Temperatures exceed 10 million K

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Prominences - Prominences - filaments seen from the side.

•Quiescent Prominences

•Active Prominences

•Eruptive Prominences

Filaments - Filaments - cool streamers of gas above photosphere

Plages - Plages - heated by rising magnetic field - compresses gas

Filaments, Plages, Filaments, Plages, Prominences :Prominences :

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Limb Limb DarkeningDarkening

The photosphere is hotter as you go deeper

We see deeper when looking at the center of the “disk”

Brightness increases as T4 (Stefan-Boltzmann Law)11

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Solar Solar WindWindOuter atmosphere is flowing away from the

Sun - the solar wind

Speeds up to few million km/hr

Earth is inside the solar wind!

At Earth:

V = 400 - 700 km/s

T = 50,000-500,000 K*

density = 103 - 104/m3

(Earth at sea level - ~2.5x1025/m3)

Solar wind expands outward,

creating the heliosphere12

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Sunspots:

•Appear in groups

•T~4000-4500 K

•Darker than surrounding photosphere

•Large magnetic fields inhibit convection

umbra

penumbra

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Solar Magnetic Solar Magnetic Field:Field:

The heliospheric current sheet extends to the outer reaches of the Solar System, and results from the influence of the Sun's rotating magnetic field on the plasma in the interplanetary medium.

Sun is a Magnetically active Star

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Sun’s Effects on Sun’s Effects on Earth:Earth:

15Earth’s greenhouse Earth’s greenhouse gasesgases

The Average Temperature The Average Temperature Profile of Earth's AtmosphereProfile of Earth's Atmosphere

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ConcluConclusionsion• Never see the Sun directly, it can damage

eyes

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