1. How do we know how far things are away from Earth in the night sky?
Parallax
How do we know how far things are away from Earth in the night sky?

2. Objectives of this powerpoint
To understand what a light year is.
To see how we determine things in the night sky that are far away and things that are close.
To understand what a large parallax angle means.
To get ready for our parallax lab activity today!

3. How fast is light?
If you shine a flashlight out into space the light travels very fast…7 times around the world in one second…that’s fast. That’s the speed of light.
186,000 miles in one second! 300,000 kilometers (km) each second.

4. What is a light year?
A light year is a measure of distance, like a foot, or a yard or a mile…only a lot bigger.

5. Definition: A light year
How far your light ray from your flashlight would go in a whole year of traveling.
This turns out to be a long way…6 trillion miles!
6,000,000,000,000 miles! 10 trillion kilometres

6. Some distances using light-years.
Our Solar system
-Much less than 1 light year.
To our nearest star
-about 1 light year
Our Milky Way Galaxy
-100,000 light years

7. What do we see in the night sky?
Why do some things move around and others stay fixed?
What do we see in the night sky?

8. Now we do the Stargazers WS
Things that move around in our sky
Things that stay fixed
Sun
Moon
Comets
Asteroids
Meteors
Planets
Stars
Galaxies
Nebulae
Things that move around in our sky night after night are….much closer than things that are far away….this is caused by “parallax”

10. What is parallax?
Parallax is the difference in position when something is seen from two points of view.

11. Try this….
Hold your finger up at arm’s length, look at the lines on the screen and close one eye while looking at your finger. Now close the other eye. Do you see a difference?
If you notice the finger jumping around…that’s parallax.

12. Now hold your finger closer to your face and do the same thing.
Do you see how that amount of shifting of your finger increases the closer the finger is to your face? That’s parallax.

13. Very Distant Background Stars
Parallax
A star is observed against a background of distant stars at 6-month intervals t1 p p
Earth’s orbit
Nearby Star t2
2 x p
Very Distant Background Stars t2 t1
On photographic plates, the nearby star appears to shift back and forth with respect to the distant background stars

14. Very Distant Background Stars
Parallax
A star is observed against a background of distant stars at 6-month intervals t1
Trig Parallax = p p
Earth’s orbit
More Distant Star t2
2 x p
Very Distant Background Stars t2 t1
On photographic plates, the nearby star appears to shift back and forth with respect to the distant background stars

15. Check for understanding…
Large distance = small parallax angle
Small Distance =Large parallax angle
=Far away
=Close

16. Using this technique, the distances to the stars are figured out.
Things like the planets have a large parallax angle = close by
Things like the other stars and galaxies, small parallax angle.
Truly the farthest objects away from us seem to hardly move at all. Almost no parallax shift.

17. Pop Quiz Questions What is the definition of a light year?
a. The direction light goes in a year.
b. The time it takes for light to travel to the Sun.
c. The distance that light goes in one year
d. The speed that light travels around the Earth

18. Pop Quiz Questions 2 Which item does NOT move around in our night sky?
a. A far away star.
b. A comet
c. An asteroid
d. A planet

19. Pop Quiz Questions 3
What does it mean if something moves around in our night sky?
a. The object is close to us
b. The object is far away from us
c. It is impossible to tell, because of geometry
d. It means that the sun is burning hydrogen

20. Pop Quiz Question 4 Parallax is ___________.
a. A type of surfboard wax
b. A method for determining how far away astronomical objects are from Earth.
c. A large star in giant phase.
d. A mitochondrial abstraction

21. Pop Quiz Questions 5
If a star has a large parallax shift, what does this mean?
a. The object is close to us
b. The object is far away from us
c. It is impossible to tell, because of geometry
d. It means that the sun is burning hydrogen

22. Now for your lab… you will measure and graph some parallax of your own.
You will need 1 partner for the activity.
You will need 1 set up, which includes the parallax sheet , a lab sheet and a golf tee.
This activity will help clarify the concept of a large versus a small parallax angle.