1. Optical Telescopes, Radio Telescopes and Other Technologies Advance Our Understanding of Space
Unit E: Topic Three

2. 3.3 Using Technology to Interpret Space

3. Using Technology to Interpret Space
Just by looking, we can’t tell how far away a star is, what its composition is, or whether it is moving toward or away from us.
Two ways to measure distance
Triangulation
Parallax
We measure motion by looking at distortion to the waves
Doppler effect
Red shift
We measure composition by looking at spectra

4. Triangulation
 measurement of a series of triangles to find the distances and relative positions of points 

5. Triangulation Procedure

7. Parallax
The apparent shift in position of a nearby object when the object is viewed from two different places.
Try it – hold out your arm and put stick out your thumb. Close your right eye, now open it and close your left eye.
Purpose: It is used to find out how far a star is away from earth.
Longer baseline = more accurate results.
Astronomers use a star’s parallax to determine what angles to use for triangulation

8. Determining a Star’s Direction of Motion
Doppler Effect: The apparent change in frequency of sound, light, and other waves as the observer and the wave source move towards or away from each other.
We know the motion of the vehicle by the pattern of the waves.

9. The Doppler Effect
The siren’s change in pitch is called the Doppler Effect and is caused by the change in a sound’s wavelength.

10. Sound waves are compressed in front of the vehicle as it speeds along.
This results in shorter wave length and higher pitch
Behind the vehicle the sound waves stretch out
This results in longer wavelength and lower pitch.

11. Light! Light also travels in waves
Sooooo…..
The Doppler Effect can be used to measure the speed and direction of light-emitting objects like stars
Sound waves differ in pitch as they move, Light waves differ in color

12. How will they move?
If a star is approaching you, its wavelengths become compressed
Sooo… the dark lines in the stars spectrum shift towards the blue end.
If a star is going away from you, the wavelengths will be longer
Sooo… The dark lines in the stars spectrum shift towards the red end…. RED SHIFTED!

14. Which direction?
How do you know?

15. Spectral Lines
Isaac Newton passed a beam of light through a prism and produced a spectrum of colors.
White light, is made up of ALL colors

16. Determining a Star’s Composition
This is done through the science of spectroscopy.
Definition: The study of spectra produced when a beam of light is passed through a prism.
A spectroscope is the instrument that helps us interpret the “fingerprint” of the elements that make up a star.

17. Spectroscope
A spectroscope is a device that has a narrow slit and a prism.
It takes light and passes it through this very narrow slit and through the prism
This creates much finer detail.

18. Experiment
Joseph von Fraunhofer used a spectroscope to look at the sun.
He noticed HUNDREDS of dark lines in the sun’s spectrum (solar spectrum)
These dark lines are called spectral lines

19. Gustav Kirchoff and Robert Bunsen heated all sorts of chemicals and looked at the vapors through a spectroscope
They realized …..
NOT ALL THE COLORS OF THE RAINBOW ARE PRESENT!

20. Each element has its own FINGERPRINT
No two elements are exactly the same
It is like a human’s fingerprint.
The colors that show up are unique to a certain light source.

21. Three Types of Spectra 1. Emission or bright line spectrum
If you heat a gas at low pressure (vacuum), it produces a spectrum that is only a set of bright lines of certain colors on a black background.

22. 2. Continuous Spectrum
If you heat a solid, liquid or gas at high pressure, the resulting spectra contain ALL THE COLORS blending into one another.
Like a rainbow in the sky.

23. 3. Absorption or Dark Line Spectrum
When white light is passed through a cooler gas, the spectrum is a continuous spectrum with dark gaps between colors
The gas that the light passes through absorbs or removes some of the colors in the spectrum

24. Spectroscopy for Astronomers
Review – THREE TYPES OF SPECTRA
1. Emission (Bright Line) Spectrum
2. Continuous Spectrum
3. Absorption (Dark Line) Spectrum

25. Example
Hydrogen
Helium
Sodium
Star 1
Star 2

27. Determining a Star’s Direction of Motion
Light travels in waves just like sound
When a star approaches, wavelengths compress and get shorter. The spectral lines move to the blue (where shorter wavelengths are)
When a star moves farther away, wavelengths lengthen. The spectral lines move to the red (where longer wavelengths are).

29. Application of the Doppler Effect
Radar Gun
It will emit a radio signal with a known wavelength
A moving car returns a wavelength
The size of the difference indicates how fast the car is moving.

30. Review Questions
Explain the meaning of triangulation and give an example of a situation in which it might be used.
What is a spectrum?
What can a star’s spectrum indicate about a star?
What is the Doppler effect?
Explain why the spectra of some stars shift.
What is the advantage of using telescopes in an array?
You are the owner of a company that wants to build the largest optical telescope in the world. Which type would you choose and why?
Why can radio astronomers make observations at any time during the day, but optical astronomers are mostly limited to making their observations at night?
Why do different elements in a star display different patterns of spectral lines?

31. Unit Three Quiz