Explain how redshift suggests that the Universe is expanding.
Stars in a faraway galaxy emit radiation. The total luminosity of the stars in the galaxy is $1.90 \times 10^{36}\,\text{W}$. The radiation from the galaxy is observed on the Earth to have a radiant flux intensity of $8.42 \times 10^{-16}\,\text{W m}^{-2}$. Determine the distance $d$ of the galaxy from the Earth.
The emission spectrum of the radiation includes a line X at a wavelength of $658\,\text{nm}$. In the observed emission spectrum, line X is found at a wavelength of $726\,\text{nm}$. Determine the speed $v$ of the galaxy relative to the Earth.
Stars in a faraway galaxy emit radiation. The total luminosity of the stars in the galaxy is $1.90 \times 10^{36}\,\text{W}$. The emission spectrum of the radiation contains a line $X$ at a wavelength of $658\,\text{nm}$. Radiation from the galaxy is observed on the Earth. The observed radiation has a radiant flux intensity of $8.42 \times 10^{-16}\,\text{W m}^{-2}$. In the observed emission spectrum, line $X$ is at a wavelength of $726\,\text{nm}$. Determine: (i) the distance $d$ of the galaxy from the Earth (ii) the speed $v$ of the galaxy relative to the Earth.
Observations of many galaxies, such as the one in (b), provide many pairs of values of $d$ and $v$. Plotting these values reveals a pattern. On Fig. 10.1, sketch how $v$ varies with $d$.
State the name of the quantity represented by the gradient of the line in Fig. 10.1.