# 3-4 Astronomy

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```					3-4 Star Systems and Galaxies ( pp 117 -120)
∆ Star Systems and Planets (pp. 117-119)
Star Systems – 2 or more stars together

2 Stars = double star or a binary Star ( like BI-cycle)

3 Stars = triple Star

We are watching Alpha Centauri A and Alpha Centauri B right now.
Our nearest star (other than the sun) Proxima Centauri is really close to
these two stars.
We are not sure if they are a triple star or if Proxima Centauri is just
passing by them.

We’ll just have to wait and see!

Sometimes in a Binary Star – one star is much brighter than the other.
(It OUTSHINES the other so we can’t see the dimmer star). We call this
an Eclipsing Binary

Eclipse – because one is in the way of the other – just like a solar
eclipse or a lunar eclipse

Binary – because there are two stars close together

Astronomers can tell if there is an unseen second star because they
can observe the effects of its gravity on the other star that they can
see.
In fact, Astronomers thought that the star called 51 Pegasi has a
planet revolving around it because something was causing the star
they were watching to move back and forth very slightly. It couldn’t
have enough mass to be a star so it had to be a planet.
Did you know – more than 50% of the stars out in the universe are
double or triple stars ( Imagine 2-3 suns in our sky)

∆Galaxies(pp 119-120)
The galaxy in which our solar system is located is called the Milky Way.

How many galaxies are there in the universe? Billions

On the drawing of the Milky Way Galaxy, place a dot and write a
label that shows where the sun is located.

If our solar system was the size of a coffee cup, the Milky Way Galaxy would be the size of the North
American Continent.                                                                                     "

The center of the Milky Way Galaxy is about 25,000 light years from the
sun.

One light year = about 5,865,696,000,000 miles                                    - wow!!!
Spiral                Elliptical          Irregular
 Look like            Look like oval          Shape???????
pinwheel             little gas and dust     No regular shape
 Our Milky Way is      between the             Can contain lots of
a Spiral Galaxy.      stars                    gas and dust and
 Full of dust and     New stars cannot         empty space
gas                   form because            The Large
 And lots of empty     there is no gas          Magellanic Cloud
space                 and dust for a           is an Irregular
nebula                   Galaxy
 Elliptical galaxies
only contain old
stars

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 views: 4 posted: 6/2/2011 language: English pages: 3