PHY 113 Lecture Notes - Lecture 6: Oort Cloud, Angular Diameter, Meteoroid

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9 Jun 2018

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Chapter 6 The Solar System
6.1 An Inventory of the Solar System
Early astronomers knew Moon, stars, Mercury, Venus, Mars, Jupiter, Saturn, comets, and
Now known: Solar system has 166 moons, one star, eight planets (added Uranus and
Neptune), eight asteroids, and more than 100 Kuiper belt objects more than 300 km in
diameter (smaller asteroids, comets, and meteoroids)
More than 2,019 extrasolar planets have been found (as of Feb 10, 2016)
Understanding planetary formation in our own solar system helps understand its formation as
well as formation of other systems
6.2 Measuring the Planets
Distance from Sun known by Keplers laws Orbital period can be observed
Radius known from angular size (and distance)
Masses from Newtons laws
Rotation period from observations
Density can be calculated knowing radius and mass
6.3 The Overall Layout of the Solar System
All orbits except Mercury’s are close to the same plane
Because the planets orbits are close to being in a plane, it is possible for them to appear in a
straight line as viewed from Earth.
This photograph was taken in April 2002.
6.4 Terrestrial and Jovian Planets
In this scaled picture of the eight planets and the Sun, the differences between the four
terrestrial and four jovian planets are clear.
Video on the relative scale of planets:
Also (includes stars):
Terrestrial planets:
Mercury, Venus, Earth, Mars
Terrestrial planets are small and rocky, close to the Sun, rotate slowly, have weak magnetic
fields, few moons, and no rings
Jovian planets:
Jupiter, Saturn, Uranus, Neptune
Jovian planets are large and gaseous, far from the Sun, rotate quickly, have strong magnetic
fields, many moons, and rings
All have atmospheres, but they are very different; surface conditions vary as well; near
vacuum on Mercury, extremely hot on Venus
Only Earth has oxygen in its atmosphere and liquid water on its surface
Earth and Mars spin at about the same rate; Mercury is much slower, Venus is slow and
Only Earth and Mars have moons
Only Earth and Mercury have magnetic fields
Jovian planets do not have solid surfaces
(gas liquid core)
Jovian planets have strong magnetic fields
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