Astronomy Chapter 8

The most successful model of the origin of the solar system is called the nebular hypothesis. The solar system formed from a cloud of interstellar material called the solar nebula.

the chemical composition of the solar nebula by mass was 98% hydrogen and helium and 2% heavier elements.

nebula flattened into a disk which all the material orbited the center in the same direction

formed from the accretion of dust particles into planetesimals then into larger protoplanets

the four jovian planets began as rocky protoplanetary cores, similar in character to the terrestrial planets. gas then accreted in a runaway fashion

the jovian planets formed directly frmt he gases of the solar nebula. in this model the cores formed from planetesimals falling into the planets.

gravitational contraction of the center of the nebula. after 10^8 years temperatures at the protosuns center became high enough to ignite nuclear reactions that convert hydrogen into helium thus forming a true star

atronomers have detected the "wobble" of stars around which they orbit

looks for the rare situation in which planet comes between us and its parent star called a transit

• -know the true mass of the orbiting planet
• -amount by which the star is dimmed during the transit depends on how large the planet is and tells diameter
• -the transit the star's light passes through the planet's atmosphere aklows us to determine composition of the planet
• -possible to detect a light dimming when the planet goes behind the star measures the amount of radiation which tells us the planet's surface temperature

• if a star drifts through the line of sight between Earth and a more distant star the closer star's gravity acts like a lens that focuses the more distant star
• s light