how do we know how far things are away from earth in the night sky?
TRANSCRIPT
How do we know how far things are away from Earth in the night sky?
1. To understand what a light year is.2. To see how we determine things in
the night sky that are far away and things that are close.
3. To understand what a large parallax angle means.
4. To get ready for our parallax lab activity today!
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.
What is 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
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
Why do some things move around and others stay fixed?
THINGS THAT MOVE AROUND IN OUR SKY
Sun Moon Comets Asteroids Meteors Planets
THINGS THAT STAY FIXED
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”
Parallax is the difference in position when something is seen from two points of view.
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?
1 2 3 4 5 6 7 8 9
If you notice the finger jumping around…that’s parallax.
1 2 3 4 5 6 7 8 9
Do you see how that amount of shifting of your finger increases the closer the finger is to your face? That’s parallax.
ParallaxA star is observed against a background of
distant stars at 6-month intervals
Earth’s orbit
t1
t2
t2 t1
2 x
On photographic plates, the nearby star appears to shift back and forth with respect to the distant background stars
Nearby Star
Very Distant Background
Stars
Earth’s orbit
Trig Parallax =
t1
t2
t2 t1
2 x
More Distant Star
Very Distant Background
Stars
ParallaxA star is observed against a background of
distant stars at 6-month intervals
On photographic plates, the nearby star appears to shift back and forth with respect to the distant background stars
Large distance = small parallax angle
Small Distance =Large parallax angle
=Far away
=Close
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.
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
Which item does NOT move around in our night sky?
a. A far away star.
b. A comet
c. An asteroid
d. A planet
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
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
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
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.