The Roman God of Love will reach its peak brightness on Tuesday (September 25) and amateur astronomers are quite excited about it. Venus will be well placed in the evening sky, shining brightly at a magnitude of -4.6 (See The Concept of Magnitude in Astrophysics). It will be the second brightest object in the sky, only after the Moon.
The brightness of Venus depends on two factors: its phase and its distance from Earth. Since it is an inferior planet (lying closer to Sun than Earth), it has phases just like the Moon. When Venus lies between Earth and Sun, its side facing the Sun is illuminated and hence we cannot see the planet. At this point Venus is closest to Earth but we cannot see it as bright. As Venus moves along its orbit, different proportions of its surface appear to be illuminated from Earth. When it is at opposite side of the Sun, full disk of Venusian surface appears to be illuminated but at this point, it is the farthest from Earth as illustrated in the image below.
Venus reaches its brightest when it is still a crescent – with less than half of its disk illuminated. This is because it is much closer to the Earth during its crescent phases than at other times.
From India, it will be difficult to observe as it will appear no higher than 13° above the horizon. It will become visible at around 18:28 (IST) as the dusk sky fades, 13° above your south-western horizon. It will then sink towards the horizon, setting 1 hour and 25 minutes after the Sun at 19:37
From U.S.A. and Canada, Venus will be barely visible as it will be just a few degrees above the horizon at dusk. From England, Venus won’t be visible at all.