As per Astronomy, the astronomical transit or simply transit refers to the phenomenon where a small celestial body appears in front of a large celestial body. In this process, the smaller object use to hide a smaller portion of big object from viewers eyes. In simple terms, the work transit represents the situation where object that is closer to eyes use to appear smaller to the viewer as compared to the distant object. On the other side, the situation where closer objects use to appear larger enough and they try to mask the distant object completely, is known as Occultation. Considering one example for transit, it represents the planet’s motion between the Sun and the terrestrial observer. This case can happen only when we consider smaller planets such as Venus and Mercury etc. Note that, if we try to observe the same phenomenon from certain outer planet as like Mars then Earth is also observed to transit with respect to the Sun. The same terminology is used to define motion of satellite about its dedicated parent planet. The best example for this situation is the transits of Galilean satellite about Jupiter when observed from surface of Earth. It is essential to aligned at least three celestial bodies in single plane/line to cause the transit phenomenon. But in few rare situations you may also observe four bodies performing the same action. For once, such case was observed on 27th June 1586; at that time Mercury was observed to transit the Sun when observed from Venus; simultaneously, transit of the small planet Mercury was observed with respect to Saturn and similarly transit of Venus also happened with respect to Saturn. Here is one more term that readers need to know about and that is Mutual Planetary Transits. There are few extreme cases when one planet passes against another planet; in this case the closer planet use to appear smaller as compared to the distant planet and this event is well known by the name Mutual Planetary Transit. Types of Contacts during Transits: There are generally four different types of contacts that lead to a situation where circumference of smaller circle or disk of smaller body use to touch the circumference of disk of larger object at one definite point. History says that the most appropriate method to determine positions of several astronomical bodies is to measure the precise time for each contact point. These contacts use to happen in specific order as defined below: 1. First Contact: In this case, the smaller body use to stay completely outside the larger object or body and it keeps on moving in inward direction. 2. Second Contact: Here, the smaller body or object is already inside the area of larger body and it continuously keeps on moving inward. 3. Third Contact: Third contact is measured when the smaller celestial object is completely inside the bigger body and it is moving in outward direction. 4. Fourth Contact: For the situation where fourth contact occurs, the smaller body is found completely outside the larger body and it keeps on moving in outward direction.