1. The Structure of the Universe
Nearly all these objects are galaxies. This image represents 1/ of the whole sky.

3. Galaxy A cluster of stars (107-1012) gravitationally bound.
The previous image suggests there may be up to 125 billion galaxies +/- 20%.
Number of stars is estimated as 1010 x 125 x 109 = 1021.

4. An elliptical galaxy as seen by Hubble telescope.

5. A spiral galaxy as seen by Hubble telescope.

6. The ‘pinwheel’ galaxy M-101

7. Galaxies tend to have a ‘galactic bulge’ where density of stars is much greater.

8. Galaxies rotate around the common centre of mass.
Galaxies contain:
Stars
Planets
Interstellar gas
Radiation and charged particles
Dark matter – poorly understood but crucial in determining the fate of the Universe.

9. Dark matter
Undetectable by its emitted radiation but its presence can be inferred by its effect on visible matter.
In other words, the universe seems more massive than expected.

10. Why dark matter? Galaxies rotate much faster than expected.
Line A predicted, B observed.
Dark matter is believed to account for this discrepancy.
Galaxies don’t obey
Laws of Kepler.

11. Position of the Sun As our galaxy rotates, the Sun orbits the galaxy.
The ‘milky way’
is the galactic
bulge.

12. The milky way

13. Artist’s impression

14. Rotation speed vs distance from galactic centre. Sun’s position marked
Rotation speed vs distance from galactic centre. Sun’s position marked. Predicted in red, observed blue.

15. Problem
Our galaxy is believed to be approximately light-years across and rotating at approximately 200 kms-1. Estimate the time to make one complete orbit.

16. The Solar System

17. Mercury 0.46 to 0.31 AU From Sun (elliptical.) 88 day orbit. Temp. at
equator 100
to 700K.
No atmosphere

18. Venus ~ AU near Circular orbit. 225 day orbit. Temp. 735 K
with little variation
with latitude.
Geologically, Earth’s
twin.

19. False-colour radar image of Venus
Venus as it
would appear
without
its thick
atmosphere.

20. Earth
Earth-
No info
Needed.

21. Mars AU
689 day
Orbital period
Of 689d.
Temp. 186
To 268K.

22. Earth and Mars shown to scale.

23. Typical surface of Mars as captured by the Pathfinder mission

24. Mars’ ice cap
Is a mixture of
CO2 and
water ice.

25. Mars
The ice cap can
be seen by
a basic telescope
from Earth.

27. The asteroid belt between Mars and Jupiter

28. The Dwarf Planet Ceres is the belt’s only minor planet

30. The first Asteroid photographed by a spacecraft.

31. Jupiter
Jupiter’s immense gravitational field prevents the asteroids forming a rocky planet.
There is a large tidal force effect between Jupiter pulling one way and the Sun the other.

32. Jupiter
2.5 times the mass of the rest of the solar system combined – excluding the sun (obviously)
Has a rocky inner core but gaseous exterior.
Many moons.

33. Jupiter 67 000 km radius. Orbits approx 5 AU from the Sun.
Can you use this info to deduce the mass and hence the density of Jupiter?

34. Jupiter’s moons 63 satellites of Jupiter including Io Europa Ganymede
Callisto all observed by Gallileo ..what a legend.

36. Io 3600 km diameter Highly volcanic (perhaps due to the large tidal
forces acting on it.)

37. Europa 6th moon The one with An ocean Below its icy surface.
A very good candidate
For supporting
Simple life.

39. Ganymede

40. Callisto

41. Saturn

42. Saturn About 10 AU from the Sun
Has at least 61 satellites not including its ring system.
The largest of these is Titan.
It composes 90% of the mass in orbit around Saturn.

43. Titan – no high resolution images available

44. Uranus

45. Uranus
21 AU from Sun
1st planet discovered by telescope in 1881 by William Herschel – what a legend.
Exceedingly cold – c.50K

46. Uranus
Has 27 moons but they are not thought to be of much significance.

47. Neptune

48. Neptune 30 AU from the Sun 55K at upper atmosphere
13 moons of which the most known is Triton which was discovered about 2 weeks after Neptune.
It took 100 years to find the next one.

49. Triton photographed by Voyager

50. Pluto – elliptical orbit, 30-49 AU

51. The Kuiper belt Beyond Neptune
Consists of rocks, metals and ices very thinly distributed
Home to 3 dwarf planets – Pluto, Haumea and Makemake.

54. The Oort Cloud
Hypothesised to lie up to AU and represents the edge of the solar system
Thought to be the origin of many long period comets

56. Comets

57. In summary The solar system is extremely big.
It contains 8 main planets.
Most of these planets have moons.
Moons are often more intriguing than the planets.
We know an awful lot but there is still much more to find and learn about.