Calculate the Sun’s radius.
The Earth lies $1.50 \times 10^{11}\,\text{m}$ from the Sun. Calculate the radiant flux intensity $F$ of radiation from the Sun at a distance of $1.50 \times 10^{11}\,\text{m}$. State a unit with your answer.
Fig. 10.1 shows how the intensity of radiation emitted by the Sun varies with wavelength. A second star has the same radius as the Sun but a lower surface temperature. On Fig. 10.1, sketch a line to show how the intensity of radiation emitted by this star varies with wavelength.
Fig. 10.2 shows the visible emission spectrum of the Sun. The lines occur at wavelengths of $397\,\text{nm}$, $410\,\text{nm}$, $434\,\text{nm}$, $486\,\text{nm}$ and $656\,\text{nm}$. The Sun and a star in the Corona Borealis galaxy have similar compositions. On Fig. 10.3, sketch the emission spectrum for the star in the Corona Borealis galaxy as it would be seen from Earth. No calculations are needed.
The Corona Borealis galaxy is receding from Earth at $21400\,\text{km s}^{-1}$. Use the information in (b)(i) to calculate, in $\text{nm}$, the observed wavelength of the lowest visible energy emission for the star in the Corona Borealis galaxy.
The wavelength in (b)(ii) is used to determine a value for the surface temperature of the star in the Corona Borealis galaxy. This calculated value is not accurate. State and explain whether the temperature is too high or too low.