Download The Solar Nebula Theory Star Cluster Types of Galaxies The Milky

The Solar Nebula Theory
This theory states that our solar system was formed
approximately 5 billion years ago from a solar nebula
The solar nebula is a giant disc of spinning gas and dust
which produced our Sun and then our planets
It explains why the planets orbit the Sun in the same
direction and in the same plane
It explains why the terrestrial planets are closer to the Sun
than the gas giants
Today astronomers have discovered that some nearby young
stars have discs that stretch for billions of kilometers and they
believe that it may be the birth of a new planetary system.
Star Cluster
A group of stars held together by gravity (two types: Open star clusters and Globular clusters)
Types of Galaxies
a)
b)
c)
d)
Elliptical
Spiral
Lenticular
Irregular
(our Milky Way)
(see page 386 in text for pictures)
The Milky Way Galaxy
Our galaxy is a barred spiral galaxy with two arms
It has more than 200 billion stars and it spans more than 100
000 ly across
Our Sun is 26 000 ly from the centre of the galaxy
The central bulge consists of older stars
The spiral arms have young and middle aged stars
At the centre, there is a massive black hole (they know this because they can see effects of its
gravitational pull on stars near it)
Quasars
Quasars are galaxies that emit extremely large amounts of
energy (because of their extremely massive black hole at the
centre)
They are the most powerful energy producers of all the known
celestial objects.