2. Stars, starlight
AND
Light
Information

3. OUTCOME QUESTION(S): S1-4-06: S1-4-07:
How do astronomers measure the great distances in the universe?
S1-4-07:
What can an astronomer learn about a star by looking at light?
Vocabulary & Concepts 
Astronomical Unit Light-year
Apparent magnitude Absolute magnitude
Electromagnetic Energy Spectroscope

4. Scientific Notation (x 10X) Express very large or very small numbers
“Power of 10” equals the number of places the decimal was moved (+) large, (-) small
is x 107
is x 10-9
2.6 x is
2.6 x is
A positive exponent (107) means multiply by 10 that many times
A negative exponent (10-5) means divide by 10 that many times

5. Earth to the Sun: 1 AU = 1.5 x 108 km (150000000)
Distance and the Universe
Common to use Astronomical Unit (A.U.)
1 A.U. = distance between the Earth and the Sun
Common Distances:
Sun - Pluto: ~ 40 AU Sun - Saturn: ~ 10 AU
Sun - Jupiter: ~ 5 AU Sun - Mars: ~ 1.5 AU
So Pluto is 40x farther away from the Sun than Earth
Earth to the Sun: 1 AU = 1.5 x 108 km ( )

6. Nearest star - 4.1 x 1013 km away from Earth!
That’s 41,000,000,000,000 km!
Nearest star x 1013 km away from Earth!
This star is Proxima Centari
Light-year (LY):
The distance a beam of light travels in one year
Light moves outward fast – about 300,000 km/sec.
9.46 x 1012 km /year = 1 light-year
P. Centari is 4.3 light-years away

7. Bright stars look close, but may be very far away
Distances can be deceiving:
Bright stars look close, but may be very far away
Star Approx. Distance (LY)
P. Centari
Sirius
Betelguese
Rigel
Most distant known galaxy 15,000,000,000
Star light takes years to get to Earth – this delay means we are looking at old “images” – it’s like looking into the past…

8. Luminosity (brightness)
Star light can be used to determine temperature, composition and size (mass)
Luminosity (brightness)
There are two amounts (magnitudes) of brightness:
Apparent magnitude – brightness as we see it.
Absolute magnitude – actual brightness.
The Sun has a higher apparent magnitude, since it is so much closer than other stars

9. Star B looks brighter – more apparent magnitude
Star B is closer to us than Star A
Star B and A have the same absolute magnitude

10. Despite being cooler, the Sun is still bigger than about 95% of stars
Temperature of Colour
Colour – shows how much energy a star emits.
Colder star glows red
Hotter star glows bluish white or even blue
Colour
Temperature (oC)
Example
Blue
25,000 – 50, 000
Bluish-white
11,000 – 25,000
Rigel (Orion’s belt)
White
7,500 – 11,000
Sirius (brightest)
Yellowish-white
6,000 – 7,500
Polaris
Yellow
5,000 – 6,000
Sun
Orange
3,500 – 5,000
Red
2,000 – 3,500
P. Centauri (closest)
Despite being cooler, the Sun is still bigger than about 95% of stars

11. Notice bigger stars are not necessarily hotter…but usually brighter

12. Star Composition
Light is a type of energy called:
Electromagnetic Energy
Scientists use a spectroscope to analyse the light energy coming from stars
Spectroscope – tool that splits light into a pattern of colours, like a rainbow.

13. Showing as the “black” lines of missing energy
The elements that make the star will absorb unique parts of the spectrum as energy is released.
Showing as the “black” lines of missing energy
The black lines in the spectrum are used to identify the elements that make up the star.

14. Remember your chemistry: heated compounds give off a unique colour spectrum.
Scientists have heated elements and recorded the unique light energy patterns
The “missing” black lines in the spectra of the Sun match with the known spectra of Hydrogen but not with Mercury – so the Sun contains Hydrogen!

15. CAN YOU ANSWER THESE QUESTIONS? S1-4-06:
How do astronomers measure the great distances in the universe?
S1-4-07:
What can an astronomer learn about a star by looking at light?
Vocabulary & Concepts 
Astronomical Unit Light-year
Apparent magnitude Absolute magnitude
Electromagnetic energy Spectroscope

16. Stars, starlight
AND
The
Big Bang

17. OUTCOME QUESTION(S): S1-4-07:
What is the evidence for the Big Bang Theory?
Vocabulary & Concepts 
Electromagnetic spectrum Doppler Effect
Red Shift Big Bang Astronomy
Cosmology

18. Light /heat are types of Electromagnetic Energy
Star light can be used to determine temperature, composition and size (mass)
Light /heat are types of Electromagnetic Energy
Hot objects (like stars) radiate different types of energies too – as temperature changes so does the main energy released

19. Electromagnetic Spectrum of Energies
HEAT
Low energy High energy
Because of the shape of the waves, the colours always separate into this same organized pattern
ROY G BIV
This is why other telescopes and tools are needed – we can only access a small amount of informational energy from stars
Red light is low energy – cool
Blue is high energy - hot

20. Red-Shift and the Big Bang
There is evidence that the universe is expanding:
- Red-shift of light from stars and galaxies
- Cosmic Microwave Background Radiation
- Gravitational waves (new)
1. Light waves work exactly like any other wave:
Waves can be far apart - long wavelength
Waves can be close together - short wavelength
We’re going to focus on the oldest, and simplest – “red-shift”
Long wavelegth
Short wavelength

21. 2. Waves are also affected by motion.
Noticeable effect is called the Doppler Effect
You have experienced this effect with sound waves
Moving – compressed in front, spread out in back
Stationary:
all waves move outward evenly

22. Higher pitch Lower pitch Doppler effect: Sound waves
You brain hears the distorted wave pattern as a different sound then is really being made by the ambulance

23. Bluer colour Redder colour Doppler effect: Light waves
You brain sees the distorted wave pattern as a different colour then is really being made by the object

24. a compressed green light appears more blue
“blue shift”
a s t r e t c h e d green light appears more red
“red shift”
Your eyes don’t know what colour it “should” be, it can only interpret the waves it sees – it can’t tell the difference between “red” and “s t r e t c h e d green”

25. 3. Spectra of ALL stars / galaxies show red shift.
Far away galaxies show more red shift - faster
Evidence that the universe is expanding and speeding up too – think of it as the first half of an explosion
“red shift” spectra
“blue shift” spectra
Normal spectra

26. The universe is expanding:
Must have started out from one point – singularity
Reverse the explosion – the Universe must have started from a packed, dense mass of material under pressure
Big Bang
Rapid expansion of Universe from the singularity
Evidence suggests Universe is 14 billion years old
Scientists cannot yet explain all “how” or “why”
Not the only explanation of the universe origin
BUT beliefs are not theories – only scientific theories can be tested and proven

27. Astronomy – study of all objects in the universe.
Cosmology – study of the origin of the universe.

28. CAN YOU ANSWER THESE QUESTIONS? S1-4-07:
What is the evidence for the Big Bang Theory?
Vocabulary & Concepts 
Electromagnetic spectrum Doppler Effect
Red Shift Big Bang Astronomy
Cosmology