How do astronomers investigate distant stars and galaxies?

By analysing the light emitted from them, particularly their emission and absorption spectra , since direct techniques are limited.

What causes characteristic absorption lines to appear in a star's spectrum?

Elements in the star, predominantly hydrogen and helium , absorb some of the emitted wavelengths.

Elements in the star, predominantly .......... , absorb some of the emitted wavelengths, producing characteristic spectral lines.

Elements in the star, predominantly hydrogen and helium , absorb some of the emitted wavelengths, producing characteristic spectral lines.

True or False? The spectral lines from a distant galaxy have a different pattern to those measured on Earth.

False. The lines from a distant galaxy show the same characteristic pattern as those measured on Earth, so the element can still be identified — they are simply shifted to longer wavelengths (redshifted).

In what direction are the spectral lines from a distant galaxy shifted, and what does this indicate?

They are shifted towards the red end of the spectrum , indicating an increase in wavelength (redshift).

Define the Doppler effect .

The Doppler effect is the apparent change in wavelength or frequency of radiation from a source due to its relative motion away from or towards the observer.

What is the difference between redshift and blueshift?

Redshift occurs when a source is moving away from the observer, increasing wavelength; blueshift occurs when a source is moving towards the observer, decreasing wavelength.

Redshift is the fractional increase in .......... (or decrease in frequency) due to the source and observer receding from each other.

Redshift is the fractional increase in wavelength (or decrease in frequency) due to the source and observer receding from each other.

True or False? Redshift means that the spectral lines themselves turn red in colour.

False. Redshift means the wavelength of the spectral lines increases, shifting them towards the red end of the spectrum — the lines do not literally turn red.

Why did the discovery that almost all galaxies are redshifted lead astronomers to conclude the universe is expanding?

It showed that the space between the Earth and the galaxies must be expanding , stretching light waves as they travel and shifting them towards red.

In the balloon analogy for the expanding universe, what do the dots represent and why do they move apart?

The dots represent galaxies ; they move apart because the space between them (the rubber) stretches as the balloon inflates — the dots (galaxies) do not themselves move.

Define Hubble's law .

Hubble's law states that the recession speed of galaxies moving away from Earth is proportional to their distance from Earth.

What two types of data did Edwin Hubble use to formulate his law?

Redshift data , to determine the recession velocities of galaxies, and standard candles , to determine their distances.

The further away a galaxy is, the .......... its recession velocity.

The further away a galaxy is, the faster its recession velocity.

Define the Big Bang Theory .

The theory that the universe began in an extremely hot, dense, singular point, which then began to expand very rapidly.

What two pieces of evidence support the Big Bang Theory?

The redshift of galaxies and the expansion of the universe .

A LevelPhysicsCambridge (CIE)Flashcards25. Astronomy & CosmologyHubble’s Law & the Big Bang Theory

Hubble’s Law & the Big Bang Theory (Cambridge (CIE) A Level Physics): Flashcards

Exam code: 9702

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How do astronomers investigate distant stars and galaxies?

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Cards in this collection (21)

How do astronomers investigate distant stars and galaxies?
By analysing the light emitted from them, particularly their emission and absorption spectra, since direct techniques are limited.
What causes characteristic absorption lines to appear in a star's spectrum?
Elements in the star, predominantly hydrogen and helium, absorb some of the emitted wavelengths.
Elements in the star, predominantly .........., absorb some of the emitted wavelengths, producing characteristic spectral lines.
Elements in the star, predominantly hydrogen and helium, absorb some of the emitted wavelengths, producing characteristic spectral lines.
True or False?
The spectral lines from a distant galaxy have a different pattern to those measured on Earth.
False.
The lines from a distant galaxy show the same characteristic pattern as those measured on Earth, so the element can still be identified — they are simply shifted to longer wavelengths (redshifted).
In what direction are the spectral lines from a distant galaxy shifted, and what does this indicate?
They are shifted towards the red end of the spectrum, indicating an increase in wavelength (redshift).
Define the Doppler effect.
The Doppler effect is the apparent change in wavelength or frequency of radiation from a source due to its relative motion away from or towards the observer.
What is the difference between redshift and blueshift?
Redshift occurs when a source is moving away from the observer, increasing wavelength; blueshift occurs when a source is moving towards the observer, decreasing wavelength.
State the equation used to calculate Doppler redshift for a non-relativistic galaxy.
$\frac{Δ λ}{λ} = \frac{Δ f}{f} = \frac{v}{c}$
Where Δλ = wavelength shift (m), λ = emitted wavelength (m), Δf = frequency shift (Hz), f = emitted frequency (Hz), v = recession speed (m s^-1), c = speed of light (m s^-1)
Redshift is the fractional increase in .......... (or decrease in frequency) due to the source and observer receding from each other.
Redshift is the fractional increase in wavelength (or decrease in frequency) due to the source and observer receding from each other.
True or False?
Redshift means that the spectral lines themselves turn red in colour.
False.
Redshift means the wavelength of the spectral lines increases, shifting them towards the red end of the spectrum — the lines do not literally turn red.
Why did the discovery that almost all galaxies are redshifted lead astronomers to conclude the universe is expanding?
It showed that the space between the Earth and the galaxies must be expanding, stretching light waves as they travel and shifting them towards red.
In the balloon analogy for the expanding universe, what do the dots represent and why do they move apart?
The dots represent galaxies; they move apart because the space between them (the rubber) stretches as the balloon inflates — the dots (galaxies) do not themselves move.
Define Hubble's law.
Hubble's law states that the recession speed of galaxies moving away from Earth is proportional to their distance from Earth.
What two types of data did Edwin Hubble use to formulate his law?
Redshift data, to determine the recession velocities of galaxies, and standard candles, to determine their distances.
State the equation for Hubble's law and define its symbols.
$v = H_{0} d$
Where v = recessional velocity (m s^-1), d = distance from Earth (m), H₀ = Hubble's constant (s^-1)
What does the gradient of a graph of recession velocity against distance represent?
The Hubble constant, H₀.
The further away a galaxy is, the .......... its recession velocity.
The further away a galaxy is, the faster its recession velocity.
Define the Big Bang Theory.
The theory that the universe began in an extremely hot, dense, singular point, which then began to expand very rapidly.
What two pieces of evidence support the Big Bang Theory?
The redshift of galaxies and the expansion of the universe.
How is the age of the universe, T₀, calculated from the Hubble constant?
$T_{0} = \frac{1}{H_{0}}$
True or False?
A larger value of the Hubble constant implies an older universe.
False.
Since $T_{0} = \frac{1}{H_{0}}$ , a larger Hubble constant implies a younger universe (a smaller value of T₀).

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