Chapter 7

The Structure and the Origin of the Solar

System

وضحاها والشمس

تقدير ذلك لها لمستقر تجري والشمسالعليم العزيز

والقمر والشمس والنهار الليل آياته ومن

Sun

• The Sun is our nearest star. • 4 light years for the next nearest star.• diameter: 1,390,000 km. (1 million VE)• mass: 1.989e30 kg (331500 ME)• temperature: 5800 K (surface) 15,600,000 K

(core)   

Revolution of the Sun

• the Sun's orbit around the center of the Milky Way once every 225 million years.

• The period of time is called a cosmic year.

• The Sun has orbited the galaxy, more than 20 times during its 4.5 billion year lifetime.

Rotation of the Sun• The sun as a whole has no single period of

rotation, but different portions of its surface perform their revolutions in different times.

• At higher latitudes the sun tends to rotate more slowly.

• It is estimated that the sun’s period of rotation at the surface varies from about 25 days at the equator to about 35 days at the poles.

The center of the Sun

• very hot (about 15 million degrees Celsius) and the pressure is immense (about 100 billion times the airpressure here on Earth).

The center of the Sun

• In every second, the Sun spends 700 billion tons of protons (or: Hydrogen) in this way. And only a small fraction (0.7 percent) is turned into light.

• Right now, about half of the amount of Hydrogen in the core of the Sun has been fused into Helium. This took the sun about 4,5 billion years.

The surface of the Sun - The Photosphere

• The photosphere is the thing you see when you look at the sun .

• Each square centimeter of the solar surface emits as much light as a 6000 Watt lamp.

The surface of the Sun The Photosphere

• Solar spots are areas on the Sun where the magnetic field is much higher than elsewhere. This increases the `magnetic pressure', which in turn decreases the normal atmospheric pressure. And because of that, the temperature in the solar spots is lower than in the surrounding area.

Solar Spots

• The number of spots on the Sun isn't constant, but varies with a period of 11 years, called the solar cycle.

Solar Spots

The atmosphere of the Sun - the Corona

• The corona begins at the top of the atmosphere.• Because the corona is so thin, you can only see

it during a solar eclipse.• Extends outward from the surface several

million miles or kilometers .• . The temperature of the corona averages 2

million degrees Kelvin;

Video, Video2

Phases of the Moon

• Waxing" means growing

• "waning" means shrinking.

• "gibbous" :"swollen

on one side."

Lunar Motion• Period 29.5 (

13 hours)• 50 min late

every night.