Venus is the brightest object because its atmosphere consists of carbon dioxide and thick clouds of Sulphuric Acids which covers the planet completely. We can never see the surface of Venus unless we go into its atmosphere. Due to this reason Venus acts as a ‘Green House’. Thus the atmosphere of Venus reflects more than 95% of the light from the sun making it the brightest object in the sky. During the early periods Venus was confused for a UFO. The bright star on the top left of the picture below is the Planet Venus. We can clearly see that Venus is very bright compared to the other stars.
Venus is one of the two Inferior Planet (the other being Mercury). Inferior planets are simply planets whose orbits are within the orbit of Earth. Since Venus is the Inferior Planet we can only see the planet near the Sun i.e. either before sunrise or after sunset. When Venus is seen in the morning before sunrise it is called as the ‘Morning Star’ and when it is seen in the evening after sunset it is called as the ‘Evening Star’.
We can see Venus through our naked eye. It looks like any other star but no star can match its brightness. When you look at the planet through a telescope you can see special phenomenon which can only be noticed by the inferior planets. But Mercury is too close to the Sun and so only Venus exhibit this character very clearly. So far this phenomenon has only been noticed in the Moon, yet it is more special in Venus. This phenomenon is nothing but the ‘Phases of Venus’. It is no different from that of the Moon. Just as Moon, Venus changes its phases from ‘New Venus’ to ‘Full Venus’ and again back to ‘New Venus’. But this effect can only be viewed through a telescope.
When Venus is behind the Sun we can see the full phase of Venus. As Venus moves through its orbit it reduces its shape into a Gibbous, just like Moon. When Venus is exactly at right angles to Sun and Earth we can see Half-Venus. And as Venus continues to move around the sun and as it comes in-between the Earth and the Sun, it reduces its shape to a cresent and finally a new-Venus, exactly as that of the Moon. Yet, there is something different in its formation of phases which makes it phenomenon. During the full phase, the Venus is usually behind the sun and hence it is smaller in size due to the longer distance from the Earth. But during the cresent, Venus comes in-between Sun and Earth and hence it appears larger in size. So as Venus goes around the Sun it not only changes its shape but also its size. This phenomenon could also be seen in Mercury but to a small extent.
The picture below shows the different phases and the sizes of Venus during April-May 2004.
When Venus is exactly in between in the orbit of Earth and Sun we can see its Transit. Transit of Venus is nothing but the movement of Venus on the surface of Sun. We can see Venus as a dark spot on the sun. The picture below shows the transit of Venus over the surface of Sun. The dark spot on the Sun in the left is Venus.
The first person to notice the Phases of Venus is Galileo Galilei with his newly invented telescope. We can now see Venus at this very day as the ‘Evening Star’. We can see the planet clearly with our naked eyes. It looks just like a star but look for the brighest in the west. It is so bright that you can see the planet even before it gets dark completely. The planet will be visible until an hour or so after sunset.
If you want to look at the phases of Venus go to a planetarium nearby.