State one function of pupil of and eye

The most important function of the Pupil of ours eye is to allows the light to enter in our eye.

Some more functions of the Pupil are ⇒
1) Pupil helps in the Adaptation and Adjustment of the eye.
2) Pupil also helps in controlling the amount of light entering our eye.

Pupil is the small space between the iris of the eye. 

Hope it helps.

We can infer that star y is closer but other factors must be considered including the heat of the star, the mass, and the brightness of the star. even though star x seems dimmer it may just be less bright or contain less heat.