A Quote by Sir Martin Rees, Astronomer Royal of Great Britain



Telescopes are in some ways like time machines...
They reveal galaxies so far away that their light has taken billions of years to reach us. We in astronomy have an advantage in studying the universe, in that we can actually see the past. We owe our existence to stars, because they make the atoms of which we are formed. So if you are romantic you can say we are literally starstuff. If you're less romantic you can say we're the nuclear waste from the fuel that makes stars shine. We've made so many advances in our understanding. A few centuries ago, the pioneer navigators learnt the size and shape of our Earth, and the layout of the continents. We are now just learning the dimensions and ingredients of our entire cosmoc, and can at last make some sense of our cosmic habitat.



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Saturday, March 7, 2009

Retrograde Motion of Planets

Inferior and Superior planets: In terms of their motions in the Sky as seen from Earth, the planets are divided into two groups. The Inferior planets, Mercury and Venus, are those that orbit closer to the Sun than Earth. The remaining planets are all Superior planets.



The Retrograde that you see in the picture above is of Mars (pictures taken for more than a month) and the other faint line that you see in the background is of Uranus.

The planets generally move from West to East in the night sky. However, periodically, a planet moves from east to west for a short time.. This phenomenon is called Retrograde Motion. This is an effect of changing perspective. Superior planets such as Mars show retrograde when Earth overtakes the other planet at opposition(when Earth moves between the Superior planet and Sun). The inferior planets show retrograde motion on either side of the inferior conjunction. They overtake Earth as they pass between Earth and Sun.

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