1. Ch. 26 The Sun and the Solar System

2. The Sun’s Size, Heat, and Structure
Fusion: The process by which stars get their energy. Consists of the combining of 4 hydrogen nuclei into helium
When the nuclei fuse, some of their mass is converted into energy. The mass of the particles involved in the reaction at the start of the reaction is greater than the mass of the particles at the end. The missing mass is converted into energy. The amount of energy produced varies depending on the kinds of elements involved in the fusion reaction E=mc2

3. Layers of The Sun
Core – Radiative Zone – Convection Zone – Photosphere – Chromosphere
Core: consists of helium and hydrogen atoms in the plasma state (100 times more dense than water) 15,600,000 C
Radiative Zone: plasma; cooler than the core; 8,000,000 C to 2,000,000 C from deep to shallow
Convection Zone: made up of rising and falling currents of plasma carrying energy to the Sun’s surface where it gets radiated into space as sunlight

4. Photosphere: The visable surface of the sun
Photosphere: The visable surface of the sun. Around 6,000 C Chromosphere: The inner layer of the Sun’s atmosphere. 20,000 C extending thousands of Km above the photosphere. Distinctive reddish color due to hydrogen emitting light due to the intense temperature Prominences = dense clouds of material suspended above the Sun’s surface by magnetic fields

5. Corona: The thin outer atmosphere of the Sun
Corona: The thin outer atmosphere of the Sun. Millions of times less bright than the photosphere. Temps of 1,000,000 to 3,000,000 C

12. Venus in front of Sun

13. 1 A.U. (astronomical Unit) = 150,000,000 Km
The distance from the Sun to the Earth

14. Features of the Sun:
Sunspots: Dark spots on the photosphere. Cooler areas than the surrounding photosphere. Very strong magnetic fields (1000 times stronger than that of the surrounding photosphere)
Move from left to right across the Sun’s surface (first indication that the Sun rotates on an axis much like Earth)
Sunspot activity cycles on an average of 11 yrs between peak activity and are associated with increase solar flare activity (large explosions of light on the Sun) and cause disruptions of radio, tv, cell phone, satellite activity

15. Solar Wind: The constant stream of electrically charged particles given off from the Sun’s Corona (450 km/Sec) so they reach Earth in a few days
Earth is protected from this by our magnetic field but the interraction of the Solar Wind and the Earth’s magnetic field create the Auroras (Northern/Southern Lights)

20. Section 2 History of solar System Study
Geocentric Models: Earth is the center of the Solar System. The stars were holes in a solid celestial sphere that surrounded the Earth. Beyond the sphere was a source of intense light. The belief was then that the sphere rotated with certain patterns coming around at the same time each year
Retrograde Motion: The apparent “backwards” movement of a planet due to the Earth catching and passing that planet in its orbit around the Sun

21. Ptolemy’s Geocentric Model
Ptolemy: Greek astronomer (2nd century AD) lived in Egypt
Developed the first model that could predict the position of planets that help until the 16th century

23. Epicycles: Small circular orbits that the planets moved upon
Deferent: The orbit followed by the center of each smaller orbit

24. Copernicus’s Heliocentric Model
Nicolaus Copernicus: Polish astronomer ( )
Heliocentric model: Model where the Sun is the center of the Solar System and the Earth is a planet that moves around it.
Retrograde is caused by planets following a counterclockwise orbit at different distances from the Sun and at different speeds

25. Tycho, Kepler Planetary Motion
Tycho Brahe:Danish astronomer (16th Century)
Followed the motion of planets, and the Moon throughout its orbit and not just at particular times. He had the most precise records from before the invention of the telescope
Johannes Kepler: Tycho’s assistant. Discovered that planet’s orbits were elliptical rather than circular

26. Created 3 Laws of Planetary Motion:
1. Planets travel in elliptical orbits around the Sun with two foci or focus on each side of the center of its path. Since there are two foci, its distance from the Sun will change throughout its orbit
2. The Equal Area Law: Each planet moves around the Sun in such a way that an imaginary line joining the planet to the Sun sweeps over equal areas of space in equal periods of time. Due to this, a planet’s speed is not constant in its orbit (faster = closer to the Sun)

27. 3. The Harmonic Law = The farther a planet is from the Sun, the longer its period of revolution (2 Reasons: the orbit is longer and the planets closer to the Sun move faster) i.e. = Earth = 30 km/sec and Mercury = 49 km/sec

28. Newton’s Laws of Gravitation
Isaac Newton (1642 – 1727) = Created three laws of motion. Discovered the Law of Gravitation
The Law of Gravitation: Every mass exerts a force of attraction on every other mass and the strength of the force is proportional to each of the masses and inversely proportional to the distance between them.