SKY-WATCHER'S DIARY: Planets, Opposition and Retrograde motion

Last year season of sky watching went without any visible planet in evening sky. So, last year I spent nights watching deep sky objects like star clusters, Galaxies and nebulae. These objects are interesting and have importance in sky watching. But with telescope in hand anyone would like to watch planets. There are seven planets in our sky and in these seven planets we can observe five without help of any optical aid. These five planets are very interesting. If you have any small telescope you can observe changes on them. Mercury and Venus shows phases like Moon. On mars surface you can observe changes like dust storms and shrinking and expansion of polar cap. Jupiter shows very dynamic features on its gaseous surface. Saturn with its beautiful ring display magnificent sight in telescope.

Last year we missed them from our evening and night sky. But from last some months they are making their presence in our sky again. From Last few months Venus is stunningly bright in west horizon after sunset. In may month Jupiter was in opposition and then on 27 June Saturn was in opposition. At the end of this month on 27 July Mars is also going to be in opposition. So month by month they are making their presence and some of them are also getting closer to earth on opposition in their orbit.

Opposition is very interesting alignment of planets and it's also provide great opportunity for sky observers to see planets. At this position planets come at exactly opposite to Sun and Earth in their orbit. When planet comes at this position they rise at sunset and set at sunrise which means they stay maximum time in earth's sky. In case of Jupiter you observe its maximum surface as its day is only of 10 hours. At opposition planets reflects maximum light so appear bright at this position. Opposition is condition at which planets comes directly opposite side of Sun and Earth in their orbit. This condition applied to the Superior planets means planets beyond earth orbit like Mars, Jupiter, Saturn, Uranus and Neptune.

Different alignments of planets with respect to Earth

Different kind of alignment happen with the inferior planets which are located in between earth and sun which are Mercury and Venus. They never comes to opposition. In their case when they comes in between sun and earth its called as Inferior conjunction. At inferior conjunction if they come in plane of Sun and Earth we can see then travelling on Sun disc, its called as Transit. When they Go beyond Sun its called as superior conjunction and we can not see them as they are located exactly beyond Sun. In superior planets condition its called as conjunction. For seeing maximum part of inferior planet they must go far from sun in their orbits. This is called as planets elongation from sun. When they get maximum far from sun its called as planets Maximum or Greatest Elongation from sun. At this greatest elongation inferior planets visible in sky for more time before sunrise or after sunset.

Unlike stars planets stays in motion constantly. Apart from these conditions planets also sometimes shows retrograde motion. Planets shows motions like direct which is their regular motion in sky which is toward east (there is daily motion of planet also in which they move from east to west, this happens due to earth's rotation on it axis). Sometimes they stop and start moving westward and again stops and then again picked their regular motion. Jupiter was in retrograde motion from 9th March and it ended on 11 July this month. Retrograde motion appears when Earth in her orbit passes other planets in their respected orbit. From earth, observer see that planet is moving backward which is east to west and then again start its direct motion which is west to east. Retrograde motion is long time motion. Planet keep moving in this motion for several days. Its very interesting to observe planets such motions. In 2003 Mars showed retrograde motion which I observed, it was great experience to observe planet moving background of stars. Mars was moving notably quick. Observing planet at different alignments and motions give clear picture that how all these planets with earth move around sun that what Copernicus and Galileo said. So, keep eye on planets for next few months.