An image of the disk of the Sun shows a higher brightness at the centre compared to the edges. Explain with the aid of a sketch the reasons for this darkening at the limb of the solar disk. In images of the solar photosphere there are small regions of the solar disk, about 500 km across, which are about 2.5 times brighter that the surrounding photosphere. Assuming a temperature of 5800 K for the background photosphere, calculate the temperature of these photospheric bright points. One explanation for these bright points is that the density is lower in these regions. Explain briefly how that could produce the observed brightening.

An image of the disk of the Sun shows a higher brightness at the centre compared to the edges. Explain with the aid of a sketch the reasons for this darkening at the limb of the solar disk. In images of the solar photosphere there are small regions of the solar disk, about 500 km across, which are about 2.5 times brighter that the surrounding photosphere. Assuming a temperature of 5800 K for the background photosphere, calculate the temperature of these photospheric bright points. One explanation for these bright points is that the density is lower in these regions. Explain briefly how that could produce the observed brightening.