Tell me how to be sure.
The first thing is to see if its speed is about one hour 15, and the direction is from top to bottom, which may be a little north. If it is, it means that it is not a celestial body in the earth's atmosphere.
Secondly, let's see if it blinks. If not, then it is a planet. Now there are four stars in the western sky that can't blink after sunset, that is, four planets, namely Mercury, Venus, Mars and Saturn.
Third, look at its brightness. If its brightness is about 30 times that of the second brightest star, it also proves that it is Venus, and only Venus has such abnormal brightness. The second brightest mercury (below Venus) and arcturus (near the zenith after sunset) are indeed much brighter than Venus.
The most decisive statement is that if you look at that telescope, if you can see a face, it is conclusive evidence that it is a planet. If the telescope is better, you can see that it is like the first quarter moon, and only half of it is bright.