Our Star: The Sun Part I The Sun’s Exterior Features Chapter 26

Sun Facts:  Diameter: 109 Earth’s  Density: 1.4 g/cc  Composition: HYDROGEN & HELIUM GAS  Rotation speed: poles: 36 days equator: 25.1 days  Surface Temp K  Mass:332,000 Earth’s  Gravity: 28 x’s Earth  Tilt: 7.25˚  Distance from Earth:93 million miles (1 AU)

Our Star  It’s hard to see much similarity between the distant points of light we call stars and our sun.  Yet our Sun is a STAR, and it’s at the center of our solar system.  Even still, our Sun is a very average star

Our Star  Contains 99.9% of the mass of the solar system.  The Sun is the source of 99.9% of the energy and light here on Earth.  It is the gravitational anchor of the solar system.  The Sun and planets formed at the same time:  4-5 billions yrs. ago

The Solar “surface”  The Sun does NOT have a solid surface like Earth.  The Sun DOES have a layered structure.  It’s “surface” and layers are gas  We’ll start at the outer layers and work our way in.

The Photosphere  When you look at the Sun during the day you are seeing at the PHOTOSPHERE.  The “visible” surface of the sun.  Thin layer of gas (less than 500km deep) from which we receive the majority of the Sun’s light. Average surface temperature ~ 6000K

A Granulated Surface  The Sun’s surface usually appears featureless, except for sunspots.  Viewed at high resolution, the surface appears highly granulated.  Each granule is a BOILING, GAS BUBBLE about as big as a continent.

Chromosphere: the “Atmosphere”  The part right above the photosphere is the chromosphere.  10,000 km thick  cooler than photosphere: 4500 K  It is normally hidden because the photosphere is far brighter.  Visible during a total solar eclipse, as a pinkish aura around the solar disk due to Hydrogen gas.

Spicules flame-like spikes ‘burps” Last for 5 minutes or so. Result of magnetic disturbances Chromosphere Spicules Convecting Granules

Transition Zone to the Corona  At about 6,000 miles above the photosphere, where the transition zone becomes the corona,  Temperatures rise quickly with altitude exceed 1,000,000 K !!  Why so hot??? Maybe the interaction with the Sun’s magnetic field or sound waves.

A Luminous Crown  Corona is Latin for “crown”.  It is the region beyond the transition zone consisting of elements that have been highly ionized by the tremendous heat in the transition zone region.  extend as far as 12 times the Sun’s radius from the Sun!  Invisible except in solar eclipses.

Corona Image: Courtesy of Fred Espenak

Total Solar Eclipse November 3 rd 1994, La Lava, Bolivia

Solar Wind  This swiftly moving particle stream of gas particles is known as the solar wind.  The solar wind blows past the earth at nearly 800km/sec (1000km/sec gusts)  Due to the incredible temperatures in corona, the gases escape the gravitational pull of the Sun.  Sun is losing mass!! 2 million tons/sec. (and yet only 0.1% in its 4.6 billion years)

Earth’s magnetic field protects us from solar winds radiation

Solar Wind  The Earth is protected from this wind by its magnet field.  This magnetic field either deflects or captures charged particles from the solar wind.  Some particles get in at the poles creating aurora.  Prominent every 11 years.

Aurora Figure: (Beautiful aurora display. Image: Courtesy of University Alaska - Fairbanks.) (Photo: Courtesy of Dick Hutchinson)

Prominence A prototypical prominence structure. The curved arch of solar material wraps around the magnetic field stretching between sunspots above the photosphere into higher layers. In chaotic areas these structures can be associated with solar flares. Prominence Sunspots Photosphere S N

Prominence, Solar Flare

Solar Flares Flare photosphere  A “Solar Flare” can be a truly violent explosion from the solar surface reaching very far out from the Sun.  Flares are much more violent than prominences.  Flares often last from minutes to hours.  A large flare can release the equivalent of nearly 2 billion megatons of TNT.  These cause CMEs (Coronal Mass Ejections)

Fireworks  At the peak of sunspot cycles, prominences and solar flares occur most frequently.  They can rise 60,000 miles above the photosphere and may be visible for weeks.  Solar flares are more sudden and violent than prominences.

Galileo Sees Spots  People must have seen sunspots even before Galileo reported them.  The largest spots are visible to the naked eye.  People were reluctant to accept imperfections in the Sun, however.  The spots moved across the surface Galileo to believe the Sun rotated.

Sunspots: What Are They?  Sunspots are irregularly shaped dark areas on the face of the Sun.  They look dark because they are cooler than the surrounding material.  Not at the poles

Sunspots: What Are They?  A sunspot is not uniformly dark.  Its center, umbra, is the darkest because it is the coolest here, and is surrounded by a lighter penumbra.  One sunspot might easily be the size of Earth or larger.

Sunspot Cycles  In 1843, Heinrich Schwabe discovered a cycle to the sunspots.  The number of spots seen on the sun reaches a maximum about every 11 years.

Sun’s Magnetic Field  Sunspots are evidence of the Sun’s magnetic field.  Sunspots are in pairs which have polarity: N and S.

Sunspots: What Are They?  Sunspots sometimes persist for months.  Might appear singly, but are usually found in pairs or groups.  Pairs and groupings correlate with the presence of magnetic loops

Bellwork: Sun’s Structure Matching 1. Photospherea. has pink color 2. Chromosphereb. Seen during eclipse 3. Transition zonec. the ‘visible’ layer 4. Coronad. hottest temps. 1,000,000,000 K e. solar winds 5. Spiculesf. violent explosions 6. Solar flaresg. last 5 minutes 7. Prominencesh. arch between sunspots 8. Sunspotsi. cooler areas on surface

Sun’s Composition What is the sun made of and how do scientists know?????? Spectral Analysis

Photosphere’s Spectra Deeper layers are dense enough to radiate like a blackbody (continuous). Photosphere’s gas absorbs some of the light. The observer sees a filtered absorption spectra

ENERGY!

Suns’ Spectra  Each element has its own spectra that can be used to identify the element Combined, what COLOR does the Sun appear to us? The Sun is emitting ALL the wavelengths, we just can’t see them.

 Notice how the H spectra line up with some of the absorption lines of the sun?  What about the other lines? (What other element did we discuss that is present in the sun?)

Which color is cooler? Hotter?

Why use yellow-green?

Four Trillion Trillion Light Bulbs  The Sun produces 4x10 26 watts of power.  That’s four trillion trillion 100-watt light bulbs.  Luminosity – rate of energy production (per second)  The Sun has an average luminosity.