Red-shift

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शिक्षकों के लिए: Red-shift (Science, Physics) के लिए इस्तेमाल के लिए तैयार लेसन स्लाइड्स, रिवीज़न नोट्स — इन्हें अपने लेसन में इस्तेमाल करें, या टॉपिक को एक इंटरैक्टिव क्लास एक्टिविटी की तरह चलाएं जिसे आपके शिक्षार्थी लाइव गेम की तरह खेलें।

लेसन नोट्स

The Doppler Effect

When a wave source is stationary, its wavefronts spread out symmetrically in all directions.
If the source moves, the wavefronts become squashed in front of it and stretched out behind it.
The Doppler effect is the change in observed frequency or wavelength caused by relative motion between a source and an observer.
In front of a moving source, the wavelength decreases and the frequency increases.
Behind a moving source, the wavelength increases and the frequency decreases.
Wavelength and frequency are inversely related: if one increases, the other decreases.

Red-shift and Blue-shift

The Doppler effect affects light as well as sound.
If a light source moves away from an observer, its wavelength increases — this is called red-shift because the light shifts towards the red end of the spectrum.
If a light source moves towards an observer, its wavelength decreases — this is called blue-shift because the light shifts towards the blue end of the spectrum.
Red-shift is defined as the observed increase in wavelength of light due to the source moving away from the observer.
In the visible spectrum, red light has the longest wavelength and the lowest frequency; blue light has a shorter wavelength and higher frequency.
An increase in wavelength means a decrease in frequency, and vice versa.

Galactic Red-shift and the Expanding Universe

Light from most distant galaxies is observed to be red-shifted.
This shows that distant galaxies are moving away from the Earth and from each other.
The further away a galaxy is, the greater its red-shift and the faster it is moving away.
This relationship — distance proportional to speed — is evidence that the universe is expanding.
Red-shift is caused by space itself expanding between galaxies, which stretches the light waves as they travel.
The observed red-shift provides evidence for the Big Bang theory.

The Big Bang Theory

The Big Bang theory states that around 14 billion years ago the universe began from a very small region that was extremely hot and dense.
A giant explosion — the Big Bang — caused the universe to expand from a single point, cooling as it did so.
Each point in the universe expands away from the others; galaxies move away from each other, and the further away they are, the faster they move.
As a result of the initial explosion, the universe continues to expand today.
If you could travel back in time, galaxies would become closer together until the entire universe was a single point.
The Steady State theory was the main rival to the Big Bang until the mid-1960s; it suggested the universe has always existed and new galaxies form in the gaps as others move apart.
The Steady State theory could not explain the Cosmic Microwave Background radiation, so it is no longer accepted.

The Big Bang and expansion of the Universe

Evidence for the Big Bang: Red-shift and Supernovae

By observing light spectra from supernovae in other galaxies, astronomers found evidence that distant galaxies are receding even faster than nearby ones.
These observations were first made in 1998.
The light spectra show that light from distant galaxies is red-shifted, which is evidence that the universe is expanding.
This matches what is expected after an explosion: matter starts densely packed and moves out in all directions, with lighter matter travelling faster and further.
The galaxies that are furthest away are moving the fastest — their distance is proportional to their speed.
Tracing the expansion back to the beginning leads to the idea that the universe began with a Big Bang.

Evidence for the Big Bang: Cosmic Microwave Background (CMB) Radiation

According to the Big Bang theory, the early universe was extremely hot and dense, so it must have emitted thermal radiation.
In 1964, astronomers discovered radiation in the microwave region of the electromagnetic spectrum coming from all directions at a temperature of about 2.73 K.
This is the Cosmic Microwave Background (CMB) radiation, thought to be the remains of thermal energy from the Big Bang.
The radiation is in the microwave region because over the past 14 billion years it has been red-shifted as the universe expanded.
Initially it would have been high-energy radiation towards the gamma end of the spectrum; as the universe expanded, its wavelength increased into the microwave region.
The CMB is very uniform and has the exact profile expected from a hot body that has cooled over a very long time.
This phenomenon cannot be explained by the Steady State theory, which is why the Big Bang became the accepted model.

The CMB Map

The CMB is represented by a map showing tiny temperature variations across the sky.
Different colours represent different temperatures: red/orange/brown regions are warmer and indicate a higher density of galaxies.
Blue/green regions are cooler and indicate a lower density of galaxies.
The temperature of the CMB is mostly uniform, with minuscule fluctuations of about 0.00001 K.
This implies that all objects in the universe are more or less uniformly spread out.

Dark Energy and Dark Matter

Evidence from the rotation and motion of galaxies suggests there is much more matter in the universe than we can account for.
This unseen matter is called dark matter; its nature is not currently known.
Measurements of the expansion of the universe using supernovae suggest that the universe is starting to expand at a faster rate.
It has been suggested that this accelerated expansion is caused by dark energy pushing everything apart.
If gravity acted alone, everything might be expected to become closer together, but we observe the opposite.
Dark energy is a possible solution that could be counteracting gravity and causing the universe to expand faster.
There is still much about the universe that is not understood, including dark matter and dark energy.

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प्रैक्टिस सवाल

फ्री प्रीव्यू — 60 में से 8 सवाल। सभी देखने के लिए साइन अप करें।

1.Light from a distant galaxy is observed to be red-shifted. Which row correctly describes the change in frequency and wavelength of the light when it is observed on Earth?
Medium
- AFrequency decreases, wavelength increases
- BFrequency increases, wavelength decreases
- CFrequency decreases, wavelength decreases
- DFrequency increases, wavelength increases
2.Which of the following statements provides evidence that the universe is expanding?
Medium
- ALight from galaxies is red-shifted
- BNuclear fusion occurs in stars
- CMany stars have orbiting planets
- DStars form from large clouds of dust and gas
3.An astronomer observes that light from a galaxy has been shifted towards the blue end of the spectrum. What can be deduced about the motion of the galaxy from this observation?
Medium
- AThe galaxy is moving towards the Earth
- BThe galaxy is moving away from the Earth
- CThe galaxy is not moving relative to the Earth
- DThe galaxy is expanding
4.Light from distant galaxies appears red-shifted to observers on Earth. Which of the following ideas does this provide evidence for? 1. The Big Bang Theory 2. The Universe is expanding 3. Distant galaxies are moving both towards us and away from us
Medium
- A1 and 2
- B1 only
- C2 only
- D1, 2 and 3
5.Wavelengths observed from a distant galaxy are compared with the same wavelengths from a laboratory source, and are found to be red-shifted. Which statement about the red-shifted light is correct?
Medium
- AAll the lines move towards the 'long λ' side by the same amount
- BAll the lines move towards the 'short λ' side by the same amount
- CAll the lines move towards the 'long λ' side by different amounts
- DAll the lines move towards the 'short λ' side by different amounts
6.Which of the following is the main piece of evidence that led to the Big Bang theory becoming the accepted model over the Steady State theory?
Medium
- AThe discovery of cosmic microwave background radiation
- BThe observation that stars are powered by nuclear fusion
- CThe fact that galaxies are made up of billions of stars
- DThe observation that the Sun is a medium-sized star
7.Red-shift of light from distant galaxies provides evidence that the universe is expanding.
Easy
True or false?
8.The Big Bang theory states that the universe began from a very small region that was extremely hot and dense.
Easy
True or false?

और सवाल

9.The Steady State theory is the currently accepted model for the origin of the universe.
Medium
True or false?
10.Which of the following statements about the Big Bang theory are correct? (Select all that apply.)
Hard
- AThe universe began about 14 billion years ago
- BThere was a giant explosion known as the Big Bang
- CThe universe expanded from a single point
- DThe universe heated as it expanded to form the universe today
- EThe further away galaxies are, the slower they are moving
11.Which of the following are evidence for dark energy and dark matter? (Select all that apply.)
Medium
- AThe rotation and motion of galaxies suggests that there is much more matter in the Universe than we can account for
- BViewing distant supernovae suggests that the Universe is starting to expand at a faster rate
- CStars have nuclear fusion occurring at their core
- DMost of the universe is comprised of hydrogen
12.Match each term with its correct definition.
Medium
- Red-shift
- Blue-shift
- Doppler effect
- Big Bang theory
- The observed increase in wavelength of light due to the source moving away from the observer
- The observed decrease in wavelength of light due to the source moving towards the observer
- The change in frequency or wavelength due to the relative motion between a source and an observer
- The theory that the universe began from a very small, hot, dense region about 14 billion years ago
13.Place the following steps in order to describe how the Big Bang theory explains the expansion of the universe.
Medium
- The universe began from a very small, hot, dense region
- There was a giant explosion known as the Big Bang
- The universe expanded from a single point
- The universe cooled as it expanded
- Galaxies moved further apart and the further away they are, the faster they move
14.Which statement best explains why red-shift provides evidence that space itself is expanding?
Medium
- AThe light waves are stretched as space expands between galaxies, increasing their wavelength
- BThe galaxies are moving through space away from a central point
- CThe galaxies are emitting light that is naturally redder than that from the Sun
- DThe light waves are compressed as space expands, decreasing their wavelength
15.Which of the following statements about the cosmic microwave background (CMB) radiation are correct? (Select all that apply.)
Hard
- AIt is found in the microwave region of the electromagnetic spectrum
- BIt comes from all directions in space
- CIt has a temperature of about 2.73 K
- DIt is evidence for the Steady State theory
- EIt was discovered using telescopes on the Earth's surface
16.Place the following events in order to show how the universe evolved according to the Big Bang theory.
Medium
- The universe was extremely hot and dense
- The Big Bang occurred
- The universe expanded and cooled
- Galaxies formed and moved apart
- The cosmic microwave background radiation was produced
17.Match each observation with the evidence it provides.
Medium
- Light from distant galaxies is red-shifted
- Radiation in the microwave region comes from all directions
- Distant supernovae appear dimmer than expected
- Galaxies rotate faster than expected from visible matter
- The universe is expanding
- The Big Bang theory
- The expansion of the universe is accelerating
- Dark matter
18.The Big Bang theory states that the universe began from a very small region that was extremely hot and dense, and has been expanding and cooling ever since.
Medium
True or false?
19.The Steady State theory can explain the cosmic microwave background radiation.
Medium
True or false?
20.In the visible light spectrum, which colour of light has the longest wavelength and the smallest frequency?
Easy
- ARed
- BBlue
- CGreen
- DViolet
21.Which of the following statements about the Doppler effect are correct? (Select all that apply.)
Medium
- AIt is the change in frequency or wavelength due to relative motion between a source and an observer
- BThe wavelength of waves in front of a moving source decreases
- CThe frequency of waves behind a moving source increases
- DIt affects sound waves but not light waves
- EWavefronts from a stationary source spread out symmetrically
22.Match each observation to the correct description of the light received.
Medium
- A galaxy moving away from the observer
- A galaxy moving towards the observer
- A stationary source of light
- A source moving away at a greater speed
- Light is red-shifted
- Light is blue-shifted
- Spectral lines are in their normal positions
- The red-shift is larger
23.Place the following statements in order to show how an expanding universe produces increasing red-shift with distance.
Medium
- Galaxies were originally grouped together at a single point
- The universe expanded and galaxies moved apart at different speeds
- The fastest-moving galaxies travelled the furthest
- Distant galaxies therefore recede faster and show the greatest red-shift
24.A graph of red-shift against distance for many galaxies is a straight line through the origin. What does this show?
Medium
- AThe further away a galaxy is, the faster it is moving away from Earth
- BThe further away a galaxy is, the slower it is moving away from Earth
- CAll galaxies are moving towards Earth at the same speed
- DRed-shift does not depend on the distance to a galaxy
25.The light from distant galaxies is red-shifted more than the light from nearby galaxies.
Easy
True or false?
26.Which statements correctly describe how red-shift supports the Big Bang theory? (Select all that apply.)
Hard
- ALight from distant galaxies is shifted towards the red end of the spectrum
- BThe red-shift shows that galaxies are moving away from each other
- CThe greater the distance to a galaxy, the greater the red-shift observed
- DRed-shift shows that galaxies are moving through space away from a central point
- ERed-shift proves that the universe has always existed in its present state
27.Which observation provides evidence for the Big Bang theory rather than the Steady State theory?
Medium
- ARadiation in the microwave region coming from all directions at about 2.73 K
- BGalaxies are made up of many billions of stars
- CThe Sun is a star in the Milky Way
- DStars are powered by nuclear fusion of hydrogen into helium
28.Match each piece of evidence to the feature of the universe it supports.
Medium
- Red-shift of light from distant galaxies
- Cosmic microwave background radiation
- Rotation and motion of galaxies
- Viewing distant supernovae
- The universe is expanding
- The universe began hot and dense and has cooled
- There is more matter than we can account for
- The rate of expansion is increasing
29.Which statement best explains why the cosmic microwave background radiation is in the microwave region of the electromagnetic spectrum?
Medium
- AIt was emitted as microwaves during the Big Bang
- BIt was initially high-energy radiation that has been red-shifted as the universe expanded
- CIt is produced by nuclear fusion in stars today
- DIt is absorbed and re-emitted by the Earth's atmosphere
30.Which of the following are reasons why dark matter and dark energy are proposed? (Select all that apply.)
Hard
- AThe rotation and motion of galaxies suggest there is much more matter than we can account for
- BMeasurements using supernovae suggest the universe is expanding at an increasing rate
- CGravity should pull everything together, but the universe is expanding instead
- DStars contain hydrogen and helium
- EThe CMB has a temperature of about 2.73 K
31.The Steady State theory also predicted that distant galaxies would show red-shift. Why is the Steady State theory no longer accepted?
Challenge
- AIt could not explain the cosmic microwave background radiation
- BIt predicted that galaxies would be blue-shifted
- CIt did not accept that the universe was expanding
- DIt could not explain why stars contain hydrogen
32.The cosmic microwave background radiation comes from all directions and is very uniform in temperature.
Medium
True or false?
33.A distant galaxy is moving away from the Earth. The wavelength of light from the galaxy is measured to be 3% longer than the same light measured in a laboratory on Earth. Which row correctly describes the frequency of this light on Earth compared with the laboratory value?
Medium
- AThe frequency is unchanged
- BThe frequency is lower
- CThe frequency is higher
- DThe frequency is 3% higher
34.An astronomer measures the spectrum of a distant supernova. The absorption lines are found to be shifted towards the red end of the spectrum by a larger amount than expected. Which of the following conclusions are supported by this observation? (Select all that apply.)
Hard
- AThe supernova is moving away from Earth.
- BThe universe is expanding.
- CThe supernova is moving towards Earth.
- DThe expansion of the universe may be accelerating.
- EThe supernova is stationary relative to Earth.
35.The cosmic microwave background radiation has a temperature of about 2.73 K and comes from all directions in space.
Easy
True or false?
36.Match each observation with the correct interpretation.
Medium
- Light from a distant galaxy is red-shifted.
- Light from a nearby star is blue-shifted.
- The cosmic microwave background is uniform and very cold.
- Galaxies further away have greater red-shift.
- The galaxy is moving away from Earth.
- The star is moving towards Earth.
- The universe has cooled as it expanded.
- The expansion of the universe is accelerating.
37.Place the following statements in order to describe how the expansion of the universe affects the light we receive from a distant galaxy.
Hard
- The galaxy emits light at specific wavelengths.
- The space between the galaxy and Earth expands.
- The light waves are stretched as they travel.
- The observed wavelength is longer than the emitted wavelength.
38.Which of the following best describes the cosmic microwave background radiation?
Medium
- ARadiation emitted by stars in distant galaxies.
- BRadiation left over from the Big Bang, now cooled and red-shifted.
- CRadiation produced by nuclear fusion in the Sun.
- DRadiation from dark matter in the universe.
39.Astronomers wanted to detect the cosmic microwave background radiation. Which of the following best explains why they were unable to do this before the 1960s?
Medium
- AMicrowaves are absorbed by the Earth's atmosphere, so telescopes had to be placed in orbit above it
- BThe cosmic microwave background radiation only began to exist in the 1960s
- CMicrowave telescopes had not yet been invented
- DThe radiation is too faint to be detected by any telescope
40.A student is comparing the light spectrum from the Sun with the light spectrum from a distant galaxy. Which statement best describes the difference they would observe?
Medium
- AThe spectral lines from the distant galaxy are shifted towards the red end of the spectrum compared with the Sun
- BThe spectral lines from the distant galaxy are shifted towards the blue end of the spectrum compared with the Sun
- CThe spectral lines from the distant galaxy are in exactly the same positions as those from the Sun
- DThe spectral lines from the distant galaxy are all missing because the light has been absorbed
41.Complete the passage about the start of the universe using the words below.
Medium
Around 14 billion years ago, the Universe began from a very small region that was extremely ____ and dense. Then there was a giant explosion, which is known as the ____. This caused the universe to ____ from a single point to form the universe today. Each point expands away from the others and the universe ____ due to this. This is seen as galaxies move away from each other, and the further away they are the ____ they move. As a result of the initial ____, the Universe continues to expand.
42.Complete the sentences about red-shift using the words below.
Medium
After the discovery of Doppler red-shift, astronomers began to realise that almost all the galaxies in the universe are ____. This led to the idea that the universe must be ____. This caused the light waves to ____ as they travel through space, shifting them towards the ____ end of the spectrum. The more shifted the light from a galaxy is, the ____ the galaxy is moving away from Earth.
43.What name is given to the observed increase in the wavelength of light from a galaxy moving away from the observer?
Medium
44.What name is given to the observed decrease in the wavelength of light from a galaxy moving towards the observer?
Medium
45.What name is given to the radiation in the microwave region that comes from all directions and is a remnant of the Big Bang?
Medium
46.What is the approximate temperature of the cosmic microwave background radiation, in kelvin (K)?
Medium
47.Complete the passage about red-shift using the words below.
Medium
An increase in the wavelength of light from a galaxy means its frequency has ____. This shift towards the ____ end of the spectrum is called red-shift. It shows that the galaxy is ____ from the observer.
48.What name is given to the unseen matter proposed to explain why galaxies rotate and move as if they contain more mass than we can see?
Medium
49.What is the temperature of the cosmic microwave background radiation? Give your answer in kelvin (K).
Easy
50.Complete the sentences about the early universe using the words below.
Medium
Around 14 billion years ago, the universe began from a very small region that was extremely ____ and dense. A giant explosion, known as the ____ ____, caused the universe to expand from a single point, cooling as it did so.
51.A galaxy is observed to have a red-shift that corresponds to a recession speed of 1.5 × 10⁴ km/s. Another galaxy is twice as far away. Assuming the Hubble relationship holds, what is the recession speed of the more distant galaxy? Give your answer in km/s.
Medium
52.Complete the sentence about the expansion of the universe.
Medium
The observation that the further away a galaxy is, the ____ it is moving away from us is evidence that the universe is ____.
53.Define the Doppler effect.
Medium
54.Explain how red-shift provides evidence for the Big Bang theory.
Hard
55.Explain why the Big Bang theory is accepted but still considered incomplete.
Hard
56.Explain how the cosmic microwave background radiation provides evidence for the Big Bang theory.
Hard
57.Explain how observations of distant supernovae since 1998 have changed our understanding of the expansion of the universe.
Hard
58.What is the approximate temperature of the cosmic microwave background radiation, in kelvin (K)?
Medium
- A3.73 K
- B1.73 K
- C2.73 K
- D4.73 K
59.What is the temperature of the cosmic microwave background radiation? Give your answer in kelvin (K).
Easy
- A4.73 K
- B3.73 K
- C1.73 K
- D2.73 K
60.A galaxy is observed to have a red-shift that corresponds to a recession speed of 1.5 × 10⁴ km/s. Another galaxy is twice as far away. Assuming the Hubble relationship holds, what is the recession speed of the more distant galaxy? Give your answer in km/s.
Medium
- A30000 km/s
- B36000 km/s
- C33000 km/s
- D27000 km/s

फ्लैशकार्ड

What is the Doppler effect?

The change in frequency or wavelength of a wave due to the relative motion between the source and an observer.

When a wave source moves away from an observer, what happens to the observed wavelength and frequency?

The wavelength increases and the frequency decreases.

When a wave source moves towards an observer, what happens to the observed wavelength and frequency?

The wavelength decreases and the frequency increases.

What is red-shift?

The observed increase in the wavelength of light from a source that is moving away from the observer.

What is blue-shift?

The observed decrease in the wavelength of light from a source that is moving towards the observer.

In the visible spectrum, which colour has the longest wavelength and which has the shortest?

Red light has the longest wavelength and the smallest frequency; blue light has a shorter wavelength and a higher frequency.

What does red-shift from distant galaxies indicate about their motion?

It indicates that the galaxies are moving away from us and from each other.

What is the relationship between a galaxy's distance from Earth and its red-shift?

The greater the distance to a galaxy, the greater its red-shift.

What does the relationship between distance and red-shift tell us about the speed of galaxies?

The further away a galaxy is, the faster it is moving away from Earth.

What does the observed red-shift of galaxies provide evidence for?

It provides evidence that the universe is expanding and supports the Big Bang theory.

What is the Big Bang theory?

The theory that around 14 billion years ago the universe began from a very small, extremely hot and dense region, and has been expanding and cooling ever since.

Why does red-shift support the Big Bang theory?

It shows that galaxies are moving apart, which is what would be expected if the universe began from a single point and has been expanding.

What did observations of supernovae in distant galaxies, first made in 1998, suggest?

That distant galaxies are receding ever faster.

What is dark matter?

Unseen matter that is proposed to explain why the rotation and motion of galaxies suggest there is much more matter in the universe than we can account for.

What is dark energy?

A proposed form of energy that could explain why the expansion of the universe appears to be accelerating, by pushing everything apart.

Why is dark energy suggested as a solution to the accelerating expansion of the universe?

Because gravity would be expected to pull everything together, but observations show the expansion is speeding up, so dark energy could be counteracting gravity.

What is the main difference between the Big Bang theory and the Steady State theory?

The Big Bang theory says the universe began from a single point and has been expanding ever since, while the Steady State theory says the universe has always existed and new galaxies form as others move apart.

Why is the Steady State theory no longer accepted?

It cannot explain the Cosmic Microwave Background radiation, which is evidence for the Big Bang.

What is the Cosmic Microwave Background (CMB) radiation?

Microwave radiation coming from all directions in space, thought to be the redshifted thermal energy left over from the Big Bang.

Why is the CMB radiation in the microwave region of the electromagnetic spectrum?

Because over about 14 billion years, the high-energy radiation from the Big Bang has been redshifted as the universe expanded, increasing its wavelength into the microwave region.

What temperature is the Cosmic Microwave Background radiation?

About 2.73 K.

What does the uniformity of the CMB radiation suggest?

That all objects in the universe are more or less uniformly spread out.

What is the difference between red-shift and blue-shift?

Red-shift is when light is shifted towards the red end of the spectrum due to the source moving away; blue-shift is when light is shifted towards the blue end due to the source moving towards the observer.

What happens to the wavelength and frequency of light when a source moves away from an observer?

The wavelength increases and the frequency decreases.

What happens to the wavelength and frequency of light when a source moves towards an observer?

The wavelength decreases and the frequency increases.

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