1. What factors make the Sun a star, not a planet?2. How long has the Sun been in existence?3. How much longer will the Sun be in existence?4. How does the Sun work? Why does it shine? Does

it produce heat? How?5. Is the Sun very similar or very different from other

stars? In what ways?6. Can solar flares really disrupt things on Earth such

as cellphone & satellite communcation? How?7. How many 100 watt light bulbs would it take to

equal the Sun’s brightness?

1. Core:The proton-protonchain happens here.

Fusion reactions combine hydrogen atoms to form helium.

Temp: 15 million K

2. Radiative Zone:Energy produced in the core is carried outward by photons.

Energy passes through gases

Temp: 1.5 million K

3. Convection Zone

“Bubbles” of hot gas transport energy to the surface.

Much more efficient than radiative zone

Temp: varies

4. Photosphere

The visible surface of the Sun

Glows yellow due to high temp

Temp: 5,800 K

It takes the average photon 170,000 years to make the trip from the core to the surface!

5. Sunspots

A magnetic “storm” on the sun’s surface

Diameters range from 2,500 km to 50,000 km

May last less than an hour or many months

Sunspots reveal that the Sun has differential rotation:

The equatorial area rotates more rapidly than the polar areas.

The Sun’s differential rotation probably causes the sunspots themselves, by leading to unusual positioning of magnetic forces.

Sunspots look dark because they are cooler, but they are still 10 times brighter than the full moon.

Temp: 3,800 K

What causes sunspots?

The Sun has a cycle of about 11 years, during which time it transitions from active to inactive, then back to active.

Sunspots are caused by magnetic field activity between 2 nearby points.

6. Prominence

An eruption of hot gas that may extend thousands of miles into space.

May last for 2 or 3 months.

A “solar flare” is a much more explosive burst of energy. They happen much more quickly.

7. Corona

The outermost layer of the Sun

The 2nd hottest part of the Sun

Temp: 10 million K

The flow of gas from the corona into space is called the “solar wind.” Its speed is about 450 km per second, so it reaches the Earth in about 4 days.

Solar Maximum

Once every 11 years, the magnetic field lines on the Sun’s surface are the most disrupted, and “solar maximum” occurs.

The most recent solar maximum was in 2001. The next will be in 2012, and astronomers think it will be the strongest solar maximum since 1958.

Many sunspots occur during solar maximum