Which instrument is used to detect infrared rays?

Heat travels through vacuum by

For a perfect black body,the absorption coefficient is

The graph shown in the adjacent diagram represents the variation of temperature $(T)$ of two bodies,$x$ and $y$,having the same surface area,with time $(t)$ due to the emission of radiation. Find the correct relation between their emissivities $(e)$ and absorptive powers $(a)$.

$A$ body,which emits radiations of all possible wavelengths,is known as

The black lines in the solar spectrum during a solar eclipse can be explained by