This document provides an introduction to the universe through 3 sentences: It begins with an overview of the contents of the universe from asteroids and comets to galaxies and galaxy clusters. Next, it describes our solar system and includes data on planets, their orbits, and surface temperatures. Finally, it discusses astronomical units of distance such as light years and compares the relative distances of objects in our solar system and galaxies.

1. presents
a production
INTRODUCTION TO
THE UNIVERSE
based on the IB Astrophysics option
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2. INTRODUCTION TO
THE UNIVERSE
What is there in the Universe?
Asteroids and comets
Moons
Planets
Stars
Nebulae
Stellar clusters
Galaxies
Galactic clusters

3. The Solar System
RELATIVE SIZES: if Sun = 100, Earth =1 ...
... and the distance between them is 10 000
They all orbit the Sun on elliptical paths

4. The Sun
Mass: 1.99 x 1030 kg
Radius:6.96 x 108 m
Surface temperature: 5800 K

5. Planets Data (and Pluto)
Planet Picture Distance to the Radius (km) Orbital Orbital Surface Density/ Satellite
Sun (km) period period day temp g/cm3 s
around its (ºC) water=1
Mercury 58 million 4 878 km axis
59 days 88 days 167 5,43 0
Venus 108 million 12 104 km -243 days 225 days 464 5,24 0
Earth 149,6 million 12 756 km 23, 93 h 365,2 15 5,52 1
days
Mars 228 million 6 794 km 24h 37min 687 days -65 3,04 2
Jupiter 778 million 142 800 km 9h 50min 12 years -110 1,32 +63
30s
Saturn 1 427 million 120 000 km 10h 14min 29,5 years -140 0,69 +56
Uranus 2 870 million 51 800 km 16h 18min 84 years -195 1,27 27
Neptune 4 497 million 49 500 km 15h 48min 164 years -200 1,77 13
Pluto 5 900 million 2 400 km 6 days 248 years -225 2 1

6. Mercury and Venus
The rocky planets closest to the Sun

7. Earth and Moon
Mariner 10
Many planets have moons which orbit
the planet (which orbits the Sun)

8. Mars
The fourth of the inner planets
Spirit Rover: Mars’ West Valley

9. Asteroid Belt
Ceres (480km):
it was the first
asteroid to be
seen. Now it’s a
dwarf planet.
Mathilde
(52km)
Eros
(13x13x33km)

10. Jupiter
The largest gas giant, 5 times more
distant from the Sun than the Earth
Jupiter and its moons: Io, Approximate size comparison
Europa, Ganymede and Callisto of Earth and Jupiter

11. Saturn
Nearly twice as far from the Sun as Jupiter
A rough comparison of the sizes
of Saturn and Earth

12. Uranus
Twice as far from the Sun as Saturn
Size comparison
of Earth and
Uranus

13. Neptune
Nearly twice as far from the Sun as Uranus
(30 times further than Earth)
Size comparison of Neptune and
Earth.

14. Astronomical units of distance
The Astronomical Unit (AU) – this is the average
distance between the Earth and the Sun.
1 AU = 150 000 000 km = 1.5x1011m

15. Astronomical distances
The light year (ly) – this is the distance travelled by light in
one year.
c = 3x108 m/s
t = 1 year = 365.25 x 24 x 60 x 60= 3.16 x 107 s
Speed =Distance / Time
Distance = Speed x Time
= 3x108 x 3.16 x 107 = 9.46 x 1015 m
1 ly = 9.46x1015 m

16. Relative distances
The Moon is 1.3 light seconds from the Earth
The Earth is 500 light seconds from the Sun
The nearest star to the Sun is about 4 light years away
The diameter of a galaxy is about 100 000 light years
The distance between galaxies is about 1 000 000 light years

17. Galaxies
A galaxy is a collection of a very large number of stars
(around 100 thousand million) mutually attracting each other
through the gravitational force and staying together. The
number of stars varies between a few million and hundreds
of billions. There are approximately 100 thousand million
galaxies in the observable universe.
There are three types of galaxies:
- Spiral (Milky Way)
- Elliptical (M49)
- Irregular (Magellanic Clouds)

18. Spiral Galaxies
Spiral galaxies consist of a rotating disk of stars
along with a central bulge of generally older stars.
Extending outward from the bulge are relatively bright
arms. There is a supermassive black hole at the
centre. The dark patches in the picture is interstellar
dust.
Milky Way

19. Spiral Galaxies
Andromeda galaxy is the closest large galaxy to Earth. It covers
about the same area of the night sky as the Moon but is much
dimmer.

20. Spiral Galaxies
Sombrero Galaxy

21. Elliptical Galaxies
M49 ESO 325-G004
Elliptical cross-section and no spiral arms.
They range in shape from nearly spherical to highly flattened
ellipsoids and in size from hundreds of millions to over one
trillion stars.
In the outer regions, many stars are grouped into globular
clusters.

22. Irregular Galaxies
Irregular galaxies have no specific structure. The
Large and Small Magellanic Clouds, the nearest
galaxies, are an example of irregular galaxies.
Small Magellanic Cloud Hoag's Object, a ring galaxy.

23. Stellar cluster
A group of stars within
a galaxy which are close
to each other, probably
held together by
gravitational attraction.
They are all in the same
direction from Earth and
the same distance away.
A stellar cluster can
contain from hundreds
to millions of stars.
Messier 69 a globular cluster, part of the Milky
Way is 30 000 ly distant and 42 ly across.

24. Constellations
A group of stars in a
recognizable pattern that
appear to be near each
other in space. They are in
the same direction from
Earth but are not
necessarily the same
distance away.
Orion includes Bellatrix (250 ly);
Betelgeuse (640 ly); Rigel (860 ly)

25. Polaris
The North star

26. How the stars seem to move
The night sky seems
to rotate around a
point above the
Earth’s axis of
rotation. In 24
hours, it completes
a full circle.
Over the course of a year, the stars are in a slightly different
position each night due to the Earth’s tilt.
Stars which are closer to the Earth also move relative to the
background of more distant stars due to the Earth’s orbit
around the Sun.

27. Nebulae
Nebulous means ‘cloud-like’
Originally, ‘nebula’ was a general name for any extended
astronomical object (the Andromeda Galaxy was referred to as
the Andromeda Nebula before galaxies were discovered by
Edwin Hubble). Nowadays, several different astronomical
objects are known as ‘nebulae’.
A nebula can be an interstellar cloud of dust, hydrogen gas and
plasma. These nebulae are often star-forming regions, such as
the Eagle nebula.
A nebula can also refer to the remains of a dying star, a
planetary nebula (eg Cat’s Eye nebula).
Or it can be a supernova remnant (eg Crab nebula).

28. Nebulae
Eagle Nebula and the Cone nebula:
star-forming regions

29. Supernova remnants
Crab Nebula - supernova remnant
Eta Carinae - supernova remnant

30. Cat’s Eye Nebula
Planetary nebulae are nebulae that form from the gaseous
shells that are ejected from low-mass giant stars when they
transform into white dwarfs.

31. Eskimo nebula
Planetary nebula 3000 ly from Earth,
discovered by William Herschel in 1787

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