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Venus at Greatest Eastern Elongation


(29th March 2004)

By Salvador J. Ribas and Francesc Vilardell

Venus is a lower planet in our Solar system, this means that it is closer to the Sunthan the Earth, and the same Mercuryoccurs with . These planets describe rather curious apparent movements due to its own motion and the motion of our planet, our position of observation.

Planetes inferiors
Fig.1. Planetary configurations for lower planets

As you can see in the figure, there are four especially relevant positions in this combination of orbits:

  • Inferior conjunction (1): It takes place when the Sun, the planet and the Earth are aligned. The orbits of these planets have slightly different orientations. So, you can see the planet going in front of the Sun only at some exceptional occasions, called transits. In case that the planet does not go in front of the Sun, it is almost impossible to observe it because, from the Earth, we are looking at the dark side of the planet.
  • Superior conjunction (2): It takes place when the planet, the and the Sun Earth are aligned. When the planet goes behind the Sun, an occultation takes place. Usually, solar occultations are not observed, because the Sun is too bright to observe the planet, even taking into account that the planet disk is fully illuminated.
  • Greatest elongations (3 and 4): The angle formed by the Sun and the planet we are looking at is called elongation (Θ in Fig.1). Greatest elongations are the optimal moments to observe the lower planets, because the solar light is less annoying. Depending on the position of the planet, there are some better times to observe it. When the planet is at the western greatest elongation (3), the best time to observe it is in the morning, just before the sunrise, to the East (E in Fig.2). When the planet is at the eastern greatest elongation (4), the best moment to observe it is in the afternoon, just after the sunset (O in Fig.2).


Fig.2. orbitsof the planets, as seen from the Earth, at the moments of greatest eastern and western elongations.

On 29th March, Venus is at the greatest eastern elongation. This configuration is optimal to see the planet during a long time after the sunset, to the west. This phenomenon is not very exceptional, since it takes place regularly, depending on the EarthVenus and orbital periods, in a csynodic periodycle called (583.92 days).

Carta de Venus

Fig.3. Stellar map produced using The Sky and Corel Draw.

Venus will be placed 46ē from the Sun at the greatest eastern elongation. It is very easy to find because, at the moment, it is a very bright dot in the Aries constellation which is going to move into the Taurus constellation and closer to the Pleiades, during the following days.

This greatest elongation is exceptional because from 29th March on Venus will reduce its elongation until going in front of the Sun on 8th June, giving rise to the Venus Transit, one of the most exceptional phenomena in astronomy.


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