The Structure & Origin of the Solar System In this section, the notes describe … The Sun

1. The Structure & Origin of the Solar System • In this section, the notes describe … • The Sun • The structure of the solar system • The appearance of the Moon in the sky and related phenomena like eclipses and tides • The origin of the solar system • However, this presentation will focus on • The properties of the Sun, and • The basic tenants of Solar Nebula Theory • For the rest of the concepts in this sections, please see the online notes. • The Sun - The central star (body) of our solar system. • It powers our planet and makes life possible. • It is approximately 8 light minutes away. (1.5x108 km, or nearly 93 million miles) • (Always use caution when viewing the Sun. Never use unfiltered telescopes, binoculars or cameras to observe the Sun!)

2. The Sun

3. The Photosphere – “Light” Sphere • The effective surface of the Sun. • It is the layer from which most of the Sun's light is emitted. • It is approximately 106 miles in diameter, • It has a temperature of ~ 5800 K. • Note: the Sun doesn't end here!

4. The Chromosphere – “Color” Sphere • The thin (~ 10,000 km) layer of the Sun's atmosphere just above the photosphere. • This layer glows with a pinkish light, due to • hydrogen emission. • It can only be seen during a total eclipse or with special filters.

5. The Corona – Latin for Crown • Corona - The uppermost level of the Sun's gases. • It is visible as a "halo" around the Moon during a total solar eclipse. • It is extremely hot, ~ 106 K! • It emits mostly x-rays.

6. The Sun’s Atmosphere The Corona The Photosphere The Chromosphere European Southern Observatory

7. The Solar Wind • Stream of charged particles (protons, electrons, alpha particle, etc.) released by the Sun as the corona continually expands into space. • Particles from the solar wind interact with the Earth and cause magnetic disturbances and the Aurora. • The solar wind stream can be enhanced by either: • Solar Flares (which trigger coronal mass ejections, or CME’s) • Coronal Holes • These phenomena on the Sun cause stronger geomagnetic storms on earth and lead to greater Auroral Activity

8. Sunspots • Sunspots are dark, relatively cool spots visible on the surface of the Sun. • Their temperatures are about 4500 K as compared to the 5800 K temperature of the photosphere. • These spots are associated with strong magnetic disturbances on the Sun, and are dark because they suppress the Sun's convective flow. • Sunspot groups are often the locations for strong solar activity, including solar flares. • The darkest central region of sunspot groups are called the umbra. • The lighter surrounding regions are known as the penumbra.

9. Sunspots • Umbra • Penumbra

10. High Resolution Image of a Sunspot Group From CSU’s Mead Observatory

11. Solar Flare on July 15, 2002 Photographed by Shawn & Christian Cruzen CSU’s Mead Observatory

12. Large Coronal Mass EjectionCaused by a solar flare on the Photosphere.

13. Aurora Borealis 4-6-00 Randy & Betty Ivins – Taken in Manchester, GA

14. Aurora Borealis 11-20-03 Randy & Betty Ivins Taken in Manchester, GA

15. Origin of the Solar System • Cosmogony - The study of the origin of the solar system. • Theories or models must take into account the many characteristics and regularities in the solar system. • Solar System Regularities: • 1. The planets' orbits are almost circular. • 2. The planets' orbits lie nearly in the same plane. (Ecliptic) • 3. All the planets revolve in the same direction around the Sun - counter clockwise as viewed from north. • 4. The Sun rotates in the same direction. • 5. Almost all the planets rotate in the same direction. (Exceptions?) • 6. Some of the planets have families of satellites that revolve around them in a manner similar to the planets around the Sun.

16. Models of Cosmogony must also account for: • The spacing of the planets' orbits • The distribution of sizes • The composition of the planets. • Early "Possible" Models: • Catastrophe Theories: The Sun collided with another star or other large body and created the planets. • Tidal Theory: A passing star gravitationally pulled the material out of the Sun and formed the planets. • Capture Theory: The Sun’s gravity captured passing planetary bodies. • Theoretical Calculations: show that material drawn out of the Sun or ejected in a collision would disperse rather than form planets by condensation. • Also, only by a few "solar systems" would form in a galaxy by the above models since collisions and near collisions are rare! • Recent observational evidence suggests that "solar systems" are common. (At Least 560!)

17. Solar Nebula Theory

18. Solar Nebula Theory • The Nebular Hypothesis: The beginnings of this model • (Nebula – gas cloud in space) • Proposed separately by Immanuel Kant (in 1755) and Pierre-Simon Laplace (in 1796) • The sun and planets formed a spinning cloud of gas; the Primeval Solar Nebula. • The mechanism that caused the collapse (maybe a supernova) would give the cloud a net spin. • I. In the plane of rotation, spin works to counteract gravity. • II. In the other dimension, gravity collapses the clouds into a disk (plane) with a net spindirection. (revolution & rotation).

19. Solar Nebula Theory • Protosun: The sun in formation; no nuclear fusion, yet. • Planetesimals: objects ~ 102 km across which formed from interstellar dust by clumping. (sticking together, then gravity). • Protoplanets: accreted out of planetesimals after ~ 107 years. • The sun condensed and fusion reactions turned on ~ 105 years. • Planets not massive enough for fusion to initiate.

20. Protoplanetseither: • 1. Condensed to form planets • 2. Collided with other protoplanets and were absorbed • Were captured by planets to form moons. (most moons simply accreted in mini-solar systems.) • Were ejected from our Solar system by gravtationalinteractions • Collisions with planetesimals may have: • 1. Fragmented and stripped off the outer layers of Mercury. • 2. Slowed Venus’s rotation. • 3. Tipped Uranus on its side. • 4. Formed the moon from the Earth.

21. • Lighter elements were probably blown to the outer solar system by violent solar winds (T Tauri winds) from the young Sun. • Billions of unused planetesimalsmay have become comets. • • Temperature decreased with distance in solar nebula. This effected composition of planets. • e.g. Little or no ice or volatiles on terrestial (inner) planets • Plenty of ice and volatiles where the gas giants formed • Terrestrial ices and atmospheres were probably enhanced by later comet impacts! • Evidence of this process of solar system formation has been observed elsewhere in our galaxy. • Examples: Beta Pictoris; Protoplanetary Disks in Orion Nebula

22. Protoplanetary Disk around Beta Pictoris

23. Protoplanetary Disks in Orion Nebula