1. Option D Lesson 1: Astronomical Objects.
Space, the final unit.
Option D Lesson 1: Astronomical Objects.

3. Solar System
We live on Earth which is one of 8 planets that orbit a star that we call “The Sun”.
The collection of bodies that orbit the sun is called the “Solar System”.
The solar system consists of planets (and their associated moons), dwarf planets, asteroids, comets and other rocky objects that are gravitationally bound to the Sun.

4. The Planets
A planet is an object that orbits a star (or stellar remnant) that is massive enough (ie has enough mass) to be rounded by it’s own gravity, and dominates it’s region of space.
To “dominate” it’s region of space, it has to have “cleared out” all the other planetoids nearby. This means that they are the only sizeable object to orbit the sun in their orbital path.

5. The Planets
Pluto shares it’s “orbital neighborhood” with other astronomical bodies - one of which is Charon, Pluto’s moon. Charon is almost as massive as Pluto (about half it’s mass…). Pluto and Charon behave almost in a “binary” manner and Pluto cannot be said to “dominate it’s neighborhood”.
Pluto is now considered a Dwarf planet

6. Orbits. All planets orbit the sun in the same direction.
The Planets follow elliptical orbits (Although they mostly “Look” Circular).
(Have you learned about ellipses in math class when studying conic sections?)
The sun is at one of the foci of the orbit.

7. Eccentricity of a circle would be e=0 E of 1 would be a straight line)
The “eccentricity” of the orbit is the ratio between the distance between the two foci of the ellipse and the length of the major axis of the ellipse.
Eccentricity of a circle would be e=0
E of 1 would be a straight line)

8. The Sun Mass: 1.99 x 1030 kg Radius:6.96 x 108 m
Surface temperature: K
Class “G” star.

9. Mercury and Venus

10. Earth and Moon
Mariner 10

11. Earth and Moon

12. Mars Spirit Rover: Mars’ West Valley
ESA’s Mars Express: Cydonia Region

13. Asteroid Belt Mathilde (52km) Eros (13x13x33km)
Ceres (480km): it was the first asteroid to be seen. Now it’s a dwarf planet.
Mathilde (52km)
Eros (13x13x33km)
The asteroid belt consists of many many many small objects (some even the size of dwarf planets) that orbit the around the sun.
The asteroid belt is between Mars and Jupiter.
Two theories exist as to it’s formation.
1 planet that broke up into many pieces.
Or a planet that could not form due to the gravitational effect of Jupiter that is nearby.

14. Kupier Belt and Trans-Neptunian objects.
Trans-Neptunian Objects (TNO) are any objects the Sun at greater distances than Neptune. (Pluto is a example TNO) There are over 1200 TNOs out there, some of which (like Pluto) that are large enough to be rounded by their own gravity, but do not dominate their orbits.
The Kuiper belt is a region of space containing rocky and icy bodies extending from the orbit of Neptune (~30 Au) out to approximately 50 Au. There are many many icy bodies and many many many comets found in the Kupier belt.
Objects in the Kuiper belt are considered TNOs

15. Jupiter Jupiter and its moons: Io, Europa, Ganymede and Calisto
Approximate size comparison of Earth and Jupiter

16. Saturn
A rough comparison of the sizes of Saturn and Earth

17. Uranus
Size comparison of Earth and Uranus

18. Neptune
Size comparison of Neptune and Earth.

19. Gas Giant vs. Terrestrial
Gas Giants
(Jovian Planets)
Terrestrial Planets
(Rocky Planets)
These planets are primarily composed of silicate rocks or metal.
Solid planetary surface.
Mercury, Venus, Earth and Mars.
No solid rock (No solid surface at all!).
Atmosphere of Hydrogen and Helium. Perhaps molten metal or rock at core.
Large >10x the mass of Earth.
Jupiter, Saturn, Uranus and Neptune.
(Uranus and Neptune are also called “Ice Giants” as they have lots of water and methane below their Hydrogen and Helium atmosphere)

20. Data about our solar system
Planet
Mass (relative to the Earth)
Radius (relative to the Earth)
Mean distance from the Sun (Au)
Mercury
0.06
0.38
0.39
Venus
0.81
0.97
0.72
Earth 1
Mars
0.11
0.53
1.52
Jupiter
318
11.2
5.2
Saturn 92
9.5
9.54
Uranus
14.5
3.7
19.2
Neptune
17.1
3.5 30
Note the “Au” is the “Astronomical Unit” , this is a distance measurement. 1 Au is the mean distance the Earth is from the Sun.

21. Solar System Data Planet Number of Moons
Average distance from sun (x106 km)
Diameter (x103 km)
Mass (x1023 kg)
Oribtal Period (in Earth years)
Eccentricity of orbit
Rotational period (Length of day in hours)
Mercury
57.9
4.9
3.3
0.24
0.206
1408
Venus
108 12 49
0.62
0.007
5832
Earth 1
150
12.8 60
0.017
23.93
Mars 2
228
6.8
6.4
1.9
0.093
24.62
Jupiter 16
778
143
19000
0.048
9.92
Saturn 18
1430
120.5
5700 29
0.056
10.66
Uranus 15
2900
51.2
866 84
0.046
17.24
Neptune 8
4500
49.5
103
165
0.01
16.11

22. Comets
A comet is a mixture of rock and ice a few kilometers in diameter. Comets are in orbit around the sun with highly elliptical orbits.
As they get close to the sun their ice begins to melt and they leave a long (many million of kilometers) trail of debris directed away from the sun.
Examples of comets are:
Halley’s Comet (Arrived in 1986 and will again in 2061)
Hale Bopp (1997 and next time in 4385)
ISON (November and after that in ???)

23. Hints…
You should probably memorize the order of the planets as you move out from the sun…
It might help to have a Mnemonic…
Mercury, Venus, Earth, Mars, Jupiter, Saturn, Uranus, Neptune.
Many Visits with Eshani Make Jonston Sleep Until Noon.
You should probably know the planets in order of size (smallest to largest both in size and mass)
Mercury Mars Venus Earth Neptune Uranus Saturn Jupiter

24. Stellar Distances.
You may have noticed that I have used different measurements of distance in this presentation.
1 AU (or Astronomical Unit) is the average distance between Earth and Sun
1Au=1.5 x 1011 m
1 Light year is the distance light travels in one year.
Since light travels at 3.0x108 m/s and in 1 year there are 60 seconds x 60minutes x 24 hours x 365 days.
1 ly = 9.46 x 1015m
Parsec (Pc) (We’ll meet this later).
Parsec stands for Parralax Second. This is the distance to a star whose “Parallax is 1 arcsecond”. This is aproximately 3.09x1016m or 3.26 light years.