Solar system lecture for HPU NCS200 earth science for elementary education summer 2014 online course

1. The solar system: a brief overview
►Formed 4.6 billion years ago from a cloud of
gas and dust (left over material from
exploding stars)
 92% hydrogen
 7.8% helium
 0.2% everything else (small but important!)
►Contracted due to its own gravity
 At some point it compressed to the point of
fusion – the sun lit up

2. The solar system: a brief overview
 The part that didn’t become the Sun was a nebular
cloud
►Nebula – rotating disc of gas and dust
 This mass of dust, etc. coalesced to form the planets
 As this mass collected it solidified and formed gravity
which attracted more material and greater gravity.
 The hydrogen & helium gases were very light and for
the smaller planets were able to achieve escape velocity
 The masses closest to the Sun were subjected to Solar
Winds

3. p.584a

4. Spinning Nebula
► Planets also form from
solar nebulas.
► The planets form from
dust and gases at the
edges of the spinning
nebula.
► The dust particles
collide with each other
and form into larger
particles. This goes on
until the particles get to
the size of boulders.
http://www.psi.edu/projects/planets/planets.html
Image credit: William K. Hartmann/PSI
The Planetary Science Institute has developed a computer model to investigate
these processes.

5. Protoplanet Forms
► These boulders collide
to form larger masses
called planetissimals.
► Planetissimals continue
to spin developing their
own gravity which
allows them to draw in
larger quantities of
particles and smaller
planetissimals and grow
into protoplanets.
http://www.psi.edu/projects/planets/planets.html
The unfinished earth by William K. Hartmann

6. The solar system: a brief overview
 This process created four inner, rocky,
terrestrial planets: Mercury, Venus, Earth &
Mars
 and four outer, gaseous, Jovian planets: Jupiter,
Saturn, Uranus and Neptune
►These were much larger and further from the Sun
and thus able to hold on to the very light gases from
the original nebula

7. Inner vs Outer Planets
► The size and make up of the planet depends on its
distance from the central star.
Farther from the central star
planets formed as ice cores with
dense gas atmospheres. They
are called the Outer Planets
Closer to the central star
planets formed as solids with
thin gas atmospheres. They
are called the Inner Planets.
http://nssdcftp.gsfc.nasa.gov/miscellaneous/planetary/other/inner_pla
nets.jpg
http://rst.gsfc.nasa.gov/Sect19/Sect19_14.
html

8. Chapter 22 – Motions in
the Heavens
Earth Science and the Environment (4th ed)
Thompson & Turk

9. 22.2 Aristotle and the
Earth-centered universe
►Geocentric – Aristotle ascribed to the idea of
an Earth-centered universe
 People have no sensation of motion so it must
be the sky that moved
 People do not fall off the Earth, so it must not
be moving
 No parallax shift of stars thus Earth does not
move.

10. 22.2 Aristotle and the
Earth-centered universe
►Parallax – an apparent change in position of
an object based on the observers change of
position
►Aristotle found no parallax shift because of the vast
distances
►Aristotle practiced science based on observation
 Model explained motion of most heavenly bodies

11. Fig. 22.5a, p.563

12. Fig. 22.5b, p.563

13. Fig. 22.5a, p.563

14. Fig. 22.5b, p.563

15. 22.3 The Renaissance and the
heliocentric solar system
►The geocentric system remained mainly
unquestioned for 1,400 years
 Copernicus – Polish astronomer found Ptolemaic
system too complicated
 Proposed a heliocentric (sun centered) model
►Accounted nicely for retrograde (backward motion)
of the planets with respect to the stars
 Brahe & Kepler – Brahe mapped all known
objects in the sky
►Kepler proposed the idea of elliptical orbits for
planets

16. Kepler’s laws
1. “The orbit of every planet is an ellipse
with the sun at a focus.”
2. “A line joining a planet and the sun
sweeps out equal areas during equal intervals
of time.”
3. “The square of the orbital period of a
planet is directly proportional to the cube of
the semi-major axis of its orbit.”

17. Kepler’s Laws

18. 22.3 The Renaissance and the
heliocentric solar system
 Galileo – astronomer, mathematician, physicist
►Realized that the laws of nature must be understood by
observation, experimentation, and analysis.
►Observed moving objects and derived the laws of
motion
 Quantified and expanded later by Newton
►Inertia – the tendency for an object to resist a change in
motion
►Thus people traveling with the Earth would realize no
motion

19. 22.3 The Renaissance and the
heliocentric solar system
 Galileo questioned the base of the Aristolean
view – and had a serious hardware (optics)
upgrade from previous astronomers
►Jupiter had 4 objects circling it
 As per a geocentric system, this was not possible
►Observed Venus had Moon-like “phases”, which
could not be explained with the geocentric model
►His Sun-centered system did not sit well with the
Catholic Church of the day - he was forced to
recant

20. 22.3 The Renaissance and the
heliocentric solar system
►Isaac Newton and the glue of the universe
 Invented calculus (EEEWWWW!!!)
 Galileo never answered why planets moved in
elliptical orbits, Newton did
►A moving body moves in a straight line unless acted
on by an outside force
►Planets were being acted on by an external force
►That force was gravity – the glue of the universe

21. The view of our
solar System
would be very
Different if not
for these
Scientific
discoveries!