The universe contains billions of galaxies, each with billions of stars. A galaxy is a group of stars held together by gravity, and the main types are spiral, elliptical, and irregular. Stars are formed from the collapse of large clouds of dust and gas, releasing heat and light through nuclear fusion. Our solar system contains 8 planets that orbit the Sun, including Earth. Copernicus first proposed the heliocentric model that planets orbit the Sun, with Kepler developing the laws of planetary motion. Newton later explained that gravity and inertia cause planets to follow elliptical orbits around the Sun.

1. Planetary Motion
&
Astronomy
Earth Science

2. THE UNIVERSE
 The Universe contains billions of galaxies
with each galaxy containing billions of
stars.
 Universe is always evolving. Everything
that exits in the universe is not
permanent. New stars are being born
while existing stars will eventually die.
 The Universe is all matter and energy.

3. THE GALAXIES
 A Galaxy is a group of stars held together
by gravity. There are billions of Galaxies.
 There are hundreds of billions of stars in a
Galaxy.
 The main three types of Galaxies are
- Spiral Galaxy
- Elliptical
- Irregular

4. Spiral Galaxy

5. Elliptical Galaxy

6. Irregular Galaxy

7. Speed of Light

8. Formation of Stars
 Stars are formed within large clusters of
dust and gases called as nebulae.
 Due to the force of gravity nebula
collapses and spin.
 The spinning clouds pull in more hydrogen
gas over millions of years.
 Collisions occurred between nebula and
hydrogen atoms.
 Hydrogen atoms combine to form helium
atoms, releasing a large amount of heat
and light

9. Energy is produced in a star's center, or core,
where pressures are enormous and
temperatures reach 27 million°F (15 million°C).
This causes nuclear fusion—atoms of hydrogen
are ripped apart and fuse (join) to form helium.
These reactions release vast amounts
of energy, which makes the starshine.

10. Overview of our Solar System
 Earth is one of the 8 planets revolving around,
or orbiting, the sun. We live in the Milky Way
Galaxy( Spiral)!

11. The Milky Way Galaxy
 It is the name of our Galaxy.
 It has spiral shape.
 It contains 200 billions stars.
 Sun is one of the star in Milky way

12.  We get the term "planet" from the Greek word
"Planetes" - meaning wanderer
 Astronomers of the International Astronomical
Union (IAU) voted on and passed the first
scientific definition of a planet in August 2006.
According to this new definition, an object must
meet three criteria in order to be classified as a
planet. First, it must orbit the Sun. Second, it
must be big enough for gravity to squash it into
a round ball.
What is a Planet

13. Why are Planets Round?
 This balance is called hydrostatic
equilibrium. A star is like a balloon. In a
balloon the gas inside the balloon pushes
outward and the elastic material supplies
just enough inward compression to
balance the gas pressure. In a star the
star's internal gravity supplies the inward
compression.

14.  All the planets, as well as most of their moon
(satellites), orbit the Sun in the same direction,
and all their orbits, lie near the same plane.
 Planets, stars, comets and galaxies make a
solar system.

15.  We have gathered much information through
the use on modern technology. Spacecraft,
telescopes (ground based & space based).

16. 3. Copernicus (1473 – 1543)

17. Copernicus…
 1st to propose that planets ORBIT around
the Sun (Heliocentrism).
 CONTROVERSIAL at the time!!!

18. 2. Tycho Brahe (1546 – 1601)

19.  Made important
contributions by
devising the most
precise instruments
available before the
invention of the
telescope for
observing the
heavens.
The astronomical
instruments of
Tycho Brahe
Tycho Brahe

20. Brahe cont…
 Brahe proposed a model of the solar
system that was intermediate between the
Ptolemaic and Copernican models (it had
the Earth at the center).
 It proved to be incorrect, but it was the
most widely accepted model of the Solar
System for the time.

21. Brahe cont…
 His observations of planetary motion,
particularly that of Mars, provided crucial
data for later astronomers like Kepler to
construct our present model of the solar
system.

22. 5. Kepler (1571 – 1630)
 Developed the 3 laws
on planetary motion.
 Described how planets
moved around the sun.

23. 1st Law (Eccentricity):
 The orbit of each planet is the shape of an
ellipse (oval –shaped) with the sun located
at one focus. (There are 2 foci in an ellipse).

24. 2nd Law (Law of Equal Areas):
 In any time interval, a line from a planet to the
sun will sweep out equal areas.
 NOTE: As the planet goes around the sun, the
further away it is, the slower it ORBITS. This is
due to the gravitational attraction between the
Sun and Earth.
 A planet sweeps out at equal amounts of area in
equal amounts of time.

25. 3rd Law (Law of Harmonies)
 The ratio of the squares of the
periods of any two planets is
equal to the ratio of the cubes
of their average distances from
the sun. P2 = a3
 P = time2 it takes to go around
the sun.
 A = distance3 from the sun.

26. Using the 3rd Law (write out):
 We can use the 3rd law to find:
a) Distance from sun.
b) Orbital period of a planet.

27. Let’s try… Determine the orbital period:
Planet Distance from
Sun (AU)
Orbital Period
P2 = a3
Mercury 0.387
Venus 0.723
Earth 1
Mars 1.524
Jupiter 5.203
Saturn 9.539
Uranus 19.191
Neptune 30.071
Pluto 39.457
0.241
0.616
1
1.88
11.9
29.5
84.0
165.0
248.0

28. The Earth’s Stalker
 The Moon stays in orbit because of
Earth's gravity. Gravity is a force that pulls
objects toward each other. Just because
an object is big does not mean it will have
lots of gravity. The force of gravity
depends on an object's mass.
 The gravity on the Moon is about 17%
what it is on the Earth. So if you weigh
200 pounds on Earth, you will weigh 34
pounds on the Moon.

29. What causes Tides
 The Moon causes tides.

30. Leap Year
 Only happens every 4 years, on February
29th.
 The earth takes 365.25 days to orbit, so it
leaves and extra day every four years.

31. Changes
 We have seasons because the earth is
tilted (wonky) as it makes its yearly
journey around the sun. The Earth's axis is
tilted at an angle of 23.5 degrees. This
means that the Earth is always "pointing"
to one side as it goes around the Sun.

32. Precession
 Change in the direction of the axis.

33. Wobble, Wobble, Wobble,
Wobble
 Nutation

34. Barycenter
The point between two objects that balance.

35. Newton’s view on planetary
motion…
 Newton proposed that the
planet’s motion is due to 2
forces: Inertia and gravity.
When combined, the planets
move in an elliptical orbit.

36.  When planet is at its farthest point from
the sun. 93 million miles!!!
Aphelion

37. Perihelion
 When a planet is at its closest point from
the sun. 91 million miles!!!

38. Planet will “sweep”
faster here.
Planet will “sweep”
slower here.
Gravity gets stronger as the planets come “near” the sun.
Time: AB = CD

39. 2. Sun’s gravity pulls
Earth. 1. Earth’s
tendency of
movement is
in a straight
line (Inertia).
Combined, it causes the planets to orbit around the sun.

40. Rotation
 The time it takes for a planet spin or
rotate on its axis once.
Examples:
a) Earth = 24 hours
b) Mercury = 59 days

41. Revolution
 The time it takes for a planet to go
around the sun once.
 Examples:
a) Earth = 1 year
b) Pluto (dwarf planet) = 248 years