Stars, RED SHIFT AND

The Big Bang

S1-4-07a Investigate how scientists examine light from stars and describe the types of information revealed.

S1-4-07b Compare and contrast scientific and cultural perspectives on the origin and evolution of the universe.

KEY WORDSLuminosity Apparent magnitudeAbsolute magnitude Electromagnetic spectrumSpectroscope Doppler Effect

Red Shift SingularityBig BangAstronomy Cosmology

Stars - classified by luminosity, temperature and mass.

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 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 and 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

Analyzing Star light

• Scientists use a spectroscope to analyse the light energy coming from stars

• Light is a type of energy called: Electromagnetic Energy

Spectroscope - splits light up into a pattern of colours, like a rainbow.

Types of Electromagnetic energy

Low energyHigh energyROY 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 the same organized pattern

• Visible section is the energy waves we can see• Energy waves we cannot see:ultraviolet, infrared, x-rays, microwaves, radiowaves, gamma rays

• Heated compounds give off a unique spectrum

The Electromagnetic Spectrum

Scientists have heated elements and recorded the unique light energy patterns

The black lines in the spectrum are used to identify the elements that make up the star.

Each element in the star absorbs unique parts of the light energy as it is released.

Showing as the “black” lines of missing energy

The “missing” black lines in the spectra of the Sun match well with the emission spectra of

Hydrogen but not with Mercury

There is evidence that the universe is expanding: - Red-shift of light from stars and galaxies - Cosmic Microwave Background Radiation - Gravitational waves (new)

ROY G BIV

We’re going to focus on the oldest, and simplest – “red-shift”

Light waves work exactly like any other wave: Waves can be far apart - long wavelength Waves can be close together - short wavelength

Waves are also affected by motion. The 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

Blue shift Red shift

• 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”

• Spectra of ALL stars and 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?

S1-4-07a:

What information can scientists get by looking at light?

How is a spectroscope used to identify star elements?

S1-4-07b:

How is the Doppler Effect used as evidence for the Big Bang?

KEY WORDSLuminosity Apparent magnitudeAbsolute magnitude Electromagnetic spectrumSpectroscope Doppler EffectRed Shift Singularity

Big BangAstronomy Cosmology