Venus at Western Elongation

inner-planets-positions   Wednesday August 12th the inner planet Venus reaches the point in its orbit called greatest western elongation. As this graphic shows the inner planet Venus, or Mercury, is more or less at a right angle (90o) from the Sun and Earth at western elongation. From the surface of the Earth, your backyard, for example, Venus is to the right, or western side of the Sun and is rising before the Sun.

   On the day of the elongation Venus will be very visible over the southeastern horizon at or before sunrise local time. Venus is joined by a few other planets, Jupiter, Uranus, Mars, and Dwarf Planet Ceres. The waning crescent Moon is nearly straight overhead (at least from 40oN) and a few degrees from the open star cluster the Pleiades. In this graphic the orbital path of Venus has been added, and also an arrow to show the direction Venus will now be moving toward (eastward).

   At western elongation Venus, or for that matter Mercury the other inner planet, is as far out from the Sun as we see them and as a result Venus or Mercury will rise at the earliest time for this orbit. Locally Venus rises that morning at around 3:00 am CDT. On the day of the western elongation Venus will be 45.8o from the Sun. From western elongation forward Venus or Mercury will be moving eastward toward the Sun and each day rising closer and closer to the time of sunrise. As the planet moves eastward it is moving further away from the Earth toward superior conjunction on the opposite side of the Sun.

    As the distance between the Earth and Venus, or Mercury, increases combined with the decreasing angle between the planet, the Earth, and the Sun, Venus or Mercury decreases in apparent size and also waxes through gibbous phase shapes but we never see it at a full phase since that is at superior conjunction.


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