Venus at Greatest Eastern Elongation
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(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
Sun
than the
Earth
, and the same
Mercury
occurs with . These planets describe rather curious apparent movements due to its own motion and the motion of our planet, our position of observation.
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.
orbits
of 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
Earth
Venus
and orbital periods, in a c
synodic period
ycle called (583.92 days).
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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