AS101 Lecture Notes - Lecture 15: Spectroscopy, Magnetic Braking, Doppler Spectroscopy
Document Summary
Two types of planets with different sizes and chemical composition. Farther away: less dense, with more hydrogen, helium, other gases and ices. Most objects in the solar system appear to have formed at about the same time, 4. 6 billion years ago. Theories can be divided into catastrophic (sudden) vs. evolutionary (gradual). Most widely accepted accepted theory is the nebular hypothesis, a. k. a. solar nebula theory which is an evolutionary explanation. Nebular hypothesis has a history going back to kant and laplace in the 18th century. Solar system begins with a large cloud of gas and dust (mostly hydrogen and helium) that begins collapsing. (balance between gravity and pressure gets upset by a shockwave from a nearby exploding star, or some other trigger. ) As the cloud collapses, its original very slight spin speeds up (like a figure skater pulling in her arms, or like a planet speeding up in its orbit as it gets closer to the sun. )
