Why is the peak net radiation approximately the same on the two dates?

March 19 and sept 24.

Explanation:

The dates of the March 19th and that of the September 24th are regarded as the two dates of the net peak radiation is almost the same. These periods are known as the March equinox and the September equinox. As this is the time when the sun rays of the sun are perpendicular to the Earth's surface at the equator. Hence the net or aggregate radiation combined is greater for these two dates.