$A$ thermopile is used for:

The temperature of the sun is measured with:

$A$ solid cylinder of length $L$ and radius $r$ is heated up to the same temperature as that of a cube of edge length $a$. If both have the same material,volume,and are allowed to cool under similar conditions,then the ratio of the amount of radiation emitted will be (Neglect radiation emitted from the flat surfaces of the cylinder).

For a perfect black body,the absorption coefficient is

If there were no atmosphere on Earth,its temperature would be ...... .

Which of the following is best close to an ideal black body?