Albert Teen
powered by
Albert logo

YOU ARE LEARNING:

pointer
Red-Shift
lessonMenuButton

Red-Shift

lesson introduction

Red-Shift

We know that far away galaxies are moving away from us because the light they emit is red-shifted.

When an ambulance is moving towards you, the sound you hear from the siren is different to when it is moving away from you. Which options best describe the difference you would hear?

hint button

You can select multiple answers

Which property of a sound wave determines the pitch of the sound?

hint button

Sound waves with a higher frequency have a higher pitch, and those with a lower frequency have a lower pitch. What can you conclude about frequency of sound waves from an ambulance siren as it moves away from you?

hint button
1

The Doppler effect

When the source of the sound wave moves towards an observer, the observed wavelength decreases and the frequency increases. The opposite is true when the source moves away from an observer. This is called the Doppler effect.

block image
2

The Doppler effect is true for light waves too.

We can use that to help us to understand more about distant stars and galaxies by studying the light from them!

block image
1

This is the electromagnetic spectrum.

In the middle, we have the visible light spectrum, which is what stars mainly emit.

block image
2

Stars produce mainly yellow light. Does red light have a shorter or longer wavelength than yellow light?

hint button
block image
3

Red light has a longer wavelength than yellow light, so how does the frequency of the light compare?

A) Red light has a higher frequency than yellow light. B) Red light has a lower frequency than yellow light.

Answer A or B.

hint button
block image
4

Remember the ambulance siren? The same effect is observed in light waves.

The frequency of the sound wave decreased when the source of the wave moved away from the observer, and increased when the source moved towards the observer. When light waves have a lower frequency, they are more red than when the frequency is higher.

block image
5

If the wavelength of light from a star in a distant galaxy has shifted from yellow light so it is closer to the wavelength of red light, the star is...

A) moving away from Earth B) moving towards Earth C) not moving

Answer A, B or C.

hint button
block image
6

If the wavelength of light from a star in a distant galaxy has shifted from yellow light so it is closer to the wavelength of blue light, the star is...

A) moving away from Earth B) moving towards Earth C) not moving

Answer A, B or C.

hint button
block image

If a star or galaxy is moving away from us, the wavelength of the light is stretched so that the light appears red. This is called a red-shift, because the spectrum of light is shifted towards the red part of the spectrum.

If a star or galaxy that is moving away from us causes a red-shift, then what might we call it if it were moving towards us?

hint button

In 1929, the astronomer Edward Hubble discovered that the light from distant galaxies was red-shifted, and the further a galaxy was from Earth, the bigger its red-shift was. Which conclusions do you think he drew from this discovery?

hint button

You can select multiple answers

1

The image shows an atomic spectra of the light from the Sun compared to that of 3 distant stars.

Atomic spectra are used to analyse the light from distant stars and galaxies. The dark lines are caused by absorption of light by atoms, such as hydrogen.

block image
2

Because the stars are made from the same chemicals, the black lines should be in the same place. But they are not! In the atomic spectra of the stars (other than the Sun), the dark lines have...

A) moved towards the blue end of the spectrum. B) moved towards the red end of the spectrum.

Answer A or B.

hint button
block image
3

This means there has been a red-shift. Has the wavelength of the stars' light increased or decreased?

hint button
block image
4

This red-shift must mean that the stars are...

A) moving towards us. B) staying still. C) moving away from us.

Answer A, B or C.

hint button
block image
5

The faster a star or galaxy is moving, the bigger the red-shift.

This must mean that the light from the most distant galaxies show the biggest red-shift.

block image
6

Which star do you think is moving away from us faster? Answer 1, 2, or 3.

hint button
block image

The faster a star or galaxy is moving, the ________ its shift will be.

hint button