1. How Big is “BIG”? Where do we fit in the universe?
Video 1
Question #1: It is said the Milky Way Galaxy is about 100,000 light-years across. Is this a time measurement? Explain.
Question #2: If a light year is a distance about 6 trillion (6,000,000,000,000) miles, how could we ever reach Alpha-Centauri, the closest star to our sun?

2. Introduction to Astronomy

3. What is Astronomy?
Astronomy is the branch of science that deals with celestial objects, space, and the physical universe as a whole.
Astronomy asks;
Where are we in the Universe?
When is Now?
How did we get here?

4. What is out there? We live on a planet (Earth).
Our planet goes around a star (Sun).
Our sun is the center of our solar system.
There are many solar systems in our galaxy (Milky Way).
There are many galaxies in the universe.

5. Our Galaxy, The Milky Way
How does anyone know what our galaxy looks like, if no one can leave it and look back?
Answer: Astronomers use evidence to guide their explanations as they imagine what the Milky Way Galaxy looks like.
Example: Using data from other galaxies we can see to describe our own galaxy.

6. Where are we in the Universe?
Video
Astronomers often say when we look at stars we are looking into the past. What do they mean by this?
Does this idea apply to the Sun? Explain

7. Where does scientific knowledge come from?
Natural Phenomena are explained through THEORIES!

8. Tool for developing possible explanations to problems.
Scientific Method
Tool for developing possible explanations to problems.

9. Scientific Method Identify the problem Make a hypothesis
Educated Guess
Experimentation
Test your Hypothesis
Analysis of results
Reject Hypothesis or Continue Testing

10. THEORIES A THEORY is a hypothesis that has survived testing!
A strong theory is one that:
Has survived the test of time!
Is supported by evidence!
Will make predictions for future research!

11. Mathematics and Astronomy
Mathematics is the language of Astronomy and all sciences.
Mathematics is used to strengthen theories that are difficult to test.
Theoretical Physicists make mathematical predictions to explain evidence or direct their research.

12. Scientific Calculations and Measurements

13. Standards of Measurement
In 1960 an international committee of scientists agreed on a system of Standards for Physical Quantities called the S.I. System (Système International).
Standard Unit for length – Meter (m)
Standard Unit for time – Second (s)
Standard Unit for mass – Kilogram (kg)

14. Metric System The SI System also includes the metric system.
The Metric System uses prefixes to represent large and small measurements.
The Metric System is divided into prefixes larger than 1 and smaller than 1
These Prefixes are based on powers of 10!

15. Metric Prefixes Prefixes Greater than “1” Kilo (k) = 1000
Mega (M) = 1,000,000
Prefixes Less than “1”
Milli (m) = 1/1000
Centi (c) = 1/100
Deci (d) = 1/10

16. Conversion Factors
Conversion Factors are used to change the unit without changing the measurement.
Conversions Factors are fractions that always equal 1!!
You may use as many conversion factors as you need to. (You can multiply by 1 anytime).
Any equality can be a Conversion Factor!

17. What is Scientific Notation?
Scientific notation is a way of writing extremely large or small measurements. The number is written as a product.

18. 1. Write number such that it is between 1 and 10.
What are the steps?
1. Write number such that it is between 1 and 10.
2. Write next factor as an exponent of 10 and count decimal places moved.

19. Adding and Subtracting Using Scientific Notation
If the exponents are the same it’s easy.
If the exponents are not the same we have to make them the same.

20. Rules for Changing Exponents
If you increase the exponent, decrease the number (move decimal to the left)
If you decrease the exponent, increase the number (move the decimal to the right)

21. Multiplying and Dividing Using Scientific Notation
Rule for multiplying:
Multiply numbers then add exponents and then multiply the units.
Rule for Dividing:
Divide numbers and then subtract the exponents and then divide the units.
Make sure your answer is in Correct Scientific Notation.

22. When is Now? The universe is believed to be 13. 7 billion years old.
The universe started with the Big Bang that filled the universe with hot glowing gas.
The fundamental forces appeared shortly after matter (hydrogen) was able to form.
No light for approximately the first 400 million years of the universe

23. When is Now?
Eventually, gravity was able to push together enough hydrogen gas to start fusion reactions and create the first stars (Population III Stars) and quasars.
Matter begins collect and Population II Stars start forming galaxies. The Milky Way Galaxy is believed to be about 9 to 10 billion years old. (About 4 billion years after the Big Bang)

24. When is Now?
Our sun and our solar system is thought to have formed about 4.5 billion years ago (Eight billion years after the Big Bang)
How long will the universe last?
No one knows for sure. Some theories talk about the “Big Freeze”, the “Big Crunch”, the “Big Rip” or the “Heat Death”

25. What are the largest structures in the universe?
Groups of Galaxies called “Super Clusters” are the biggest objects in the universe.
The Biggest of these super clusters are believed to be 200 million light-years across.
They are very old. Formed only 2 billion years after the Big Bang.
Contain over 30 concentrations of gas, each one is up to 10 times bigger than our own Milky Way galaxy.

26. Why Study Astronomy?
Astronomy looks to answer the following questions.
How did we get to this point in the history of the universe?
Where is the universe going?
How do we know the claims scientists make are true?

27. Distances for Astronomy
As you have seen miles and kilometers are too small for astronomical distances.
We use Astronomical Units (AU) for the distances in our solar system.
1 AU = 1.5 x 1011 m
This is the distance from the sun to the earth
We use light-years for distances between stars and galaxies.
1 light-year = 1 x 1016 m or 5.9 X 1012 miles