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Stars, starlight AND
The Big Bang
OUTCOME QUESTION(S):
S1-4-06:How do astronomers measure the great distances in the universe?
S1-4-07:What is the evidence for the Big Bang Theory?
Vocabulary & People Astronomical Unit Light-yearApparent magnitude Absolute magnitudeSpectroscopeElectromagnetic spectrum Doppler EffectRed Shift Big BangAstronomyCosmology
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
32 000 000.0 is 3.2 x 107
0.0000000055 is 5.5 x 10-9
2.6 x 105 is 260 000.02.6 x 10-5 is 0.000026
Putting values into Sci. Notation is a very useful skill
Distance and the Universe• Common to use Astronomical Unit (A.U.)
1 A.U. = distance between the Earth and the Sun
Sun to the Earth: 1 AU = 1.5x108 km
Common Distances:Sun - Pluto: ~ 40 AU Sun - Saturn: ~ 10 AUSun - Jupiter: ~ 5 AU Sun - Mars: ~ 1.5 AU
So Pluto is 40x farther away from the Sun than Earth
• Nearest star - 4.1x1013 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.•9.46x1012 km /year = 1 light-year•P. Centari is 4.3 light-years away
That’s 41,000,000,000,000 km!
• Distances can be deceiving: Bright stars look close, but may be very far away
Star
Approx. Distance (LY)P. Centari
4.3Sirius
8.8Betelguese
700Rigel
900Most distant known galaxy15,000,000,000
Star light takes years to get to Earth – this delay means we are looking at old “images” – it’s like looking into the
past…
Luminosity (brightness)There are two amounts (magnitudes) of brightness:
Apparent magnitude – brightness as we see it.Absolute magnitude – actually brightness.
The Sun has a higher apparent magnitude, since it
is so much closer than other stars
Star light can be used to determine temperature, composition and size (mass)
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
Temperature of ColourColour – 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
Notice bigger stars are not necessarily hotter…but usually
brighter
Star Composition
• Scientists use a spectroscope to analyse the light energy coming from stars
• Light is a type of energy called: Electromagnetic Energy
Spectroscope – tool that splits light into a
pattern of colours, like a rainbow.
The black lines in the spectrum are used to identify the elements that make up the star.
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
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!
Electromagnetic Spectrum of Energies
Low energy High energy
ROY G BIV
Red light is low energy – cool
Blue is high energy - hot
Because of the shape of the waves, the colours always separate into this same organized pattern
HEAT
This is why other telescopes and tools are needed – we can only access a small amount of informational energy from stars
There is evidence that the universe is expanding: - Red-shift of light from stars and galaxies - Cosmic Microwave Background Radiation - Gravitational waves (new)
We’re going to focus on the oldest, and simplest – “red-shift”
1. Light waves work exactly like any other wave:• Waves can be far apart - long wavelength• Waves can be close together - short wavelength
Red-Shift and the Big Bang
Long wavelegth
Short wavelength
2. Waves are also affected by motion. • Noticeable effect is called the Doppler Effect
Stationary:all waves move outward evenly
Moving – compressed in front, spread out in back
You have experienced this effect with sound waves
Higher pitch Lower pitch
You brain hears the distorted wave pattern as a different sound then is really being made by the ambulance
Doppler effect:Sound waves
You brain sees the distorted wave pattern as a different colour then is really being made by the object
Doppler effect:Light waves
Bluer colour Redder colour
• 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 “stretched green”
3. Spectra of ALL stars / galaxies show red shift.Far away galaxies show more red shift - faster
“red shift” spectra
“blue shift” spectra
Normal spectra
Evidence that the universe is expanding and speeding up too – think of it as the first half of an explosion
The universe is expanding:• Must have started out from one point –
singularityReverse 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
Astronomy – study of all objects in the universe.
Cosmology – study of the origin of the universe.
CAN YOU ANSWER THESE QUESTIONS?
S1-4-06:How do astronomers measure the great distances in the universe?
S1-4-07:What is the evidence for the Big Bang Theory?
Vocabulary & People Astronomical Unit Light-yearApparent magnitude Absolute magnitudeSpectroscopeElectromagnetic spectrum Doppler EffectRed Shift Big BangAstronomyCosmology