1. Chapter 15 – Stars, Galaxies and the Universe

2. Chapter 15 – History of the Universe
Section 4 – Star Systems and Galaxies
Standards
4.a – Students know galaxies are clusters of billions of stars and may have different shapes
4.b – Students know that the Sun is one of many stars in the Milky Way galaxy and that stars may differ in size, temperature and color

3. Star Systems and Clusters
Most stars are members of groups of two or more stars, called star systems
(our sun is a single star)
Binary star - star system with two stars
Eclipsing binary - a system in which one star periodically blocks the light from another

4. How do they find binary star systems?
Dimming
Look for a dimming as one star passes in front of the other
Gravity
Look for a wobble as one star pulls on the other

5. Planets around other Stars
Astronomers found a planet revolving around a star – 51 Pegasi (using the same methods to detect binary stars)
video
Pegasi-51 was the first planet discovered outside our solar system
Now, astronomer have confirmed about 1000 more

6. Planets around other Stars
Astronomers have only been able to find very large planets so far
Smaller planets are difficult to see
Too much light
Not much gravity
Planets outside our solar system are called exoplanets

7. Star Clusters
Younger
Open Clusters – have a loose, disorganized appearance and contain no more than a few thousand stars
Cluster video
Globular Cluster – large groupings of older stars, round and densely packed
Older
Cluster video #2

8. Star clusters are part of galaxies

9. Galaxies
Galaxy – a huge group of single stars, star systems, star clusters, dust and gas bound together by gravity
Many large galaxies (including our own) appear to have huge black holes at their center
Quasars – an enormously bright, distant galaxy
10 billion light-years or more away – making them among the most distant objects in the universe
Quasar clip

10. Galaxies – 3 main types
Spiral Galaxy- A galaxy whose arms curve outward in a pinwheel pattern
Elliptical Galaxy- A galaxy shaped like a flattened ball, containing only old stars
Irregular Galaxy- A galaxy that does not have a regular shape

11. Milky Way Galaxy We live in the Milky Way Galaxy – a spiral galaxy
The center is about 25,000 light-years from the sun
The center is not visible from earth due to massive clouds of stars, dust and gas between the sun and the center
Milky way video clip

12. Scale of the Universe Universe – all of space and everything in it
Scientific Notation – uses powers of ten to write very large or very small numbers in shorter form
To express a number in scientific notation, first insert a decimal point in the original number so that you have a number between one and ten
To determine the power of 10, count the number of places that the decimal point moved
3,230 light-years = 3.23 x 103 light-years

13. Scientific Notation
The sun takes about 220,000,000 years to revolve once around the center of the galaxy. Express this length of time in scientific notation
2.2 X 108 years
The star Betelgeuse has a diameter of 940,000,000 km. Betelgeuse is 427 light-years from Earth. Write each of these figures in scientific notation.
9.4 X 108 km
4.27 X 102 light-years

14. Download this app
SkyView Free