Question

The Earth effectively sits in a low-density H II region made up of the ionized solar wind. The wind
has is expanding constantly at about 400 kms−1 (i.e. the density decreases as r−2) and in the region of the Earth’s orbit, Ne = 10 cm−3. Estimate t and Tb at an observing frequency of 100MHz due to free-free absorption from this wind, at large angles from the Sun.