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