Venus-Saturn Conjunction Series

Venus and Saturn 17-23 September

Venus and Saturn 17-23 September

   This evening and for the next several evenings look between the southwestern and western horizons for the very bright inner planet Venus. Just above Venus is the not nearly as bright outer planet Saturn as the page banner shows –which by the way is not drawn to scale. In this animated graphic set for 1-day intervals, Venus is moving eastward and will pass Saturn, which is also moving eastward.
   Both of these planets are in motion as each is moving at its own speed eastward as we view them from the Earth. The Sun is also moving eastward but this is an apparent motion caused by the Earth revolving around the Sun. The net result of the Earth’s actual motion and the Sun’s apparent motion is that the area of the sky where the two planets are located is moving westward and setting a bit earlier each evening. The Sun’s apparent daily motion eastward from revolution (not rotation) is at the Earth’s daily orbital rate of approximately 1 degree per day which is faster than Saturn’s daily orbital rate of approximately 0.035 degrees per day. So Saturn and its part of the sky shifts westward while Saturn is moving eastward from its own orbital motion, but obviously slower than the Sun’s apparent motion.

Venus and Saturn 17-23 September

Venus and Saturn 17-23 September

   In this simulated 7×50 binocular view of the two planets you can again see how the two planets respective daily orbital rates compare. And as you watch, the star Zubenelgenubi, a near 3rd magnitude star in the constellation Libra, moves from left to right (east to west) into the scene. Since we consider stars to be fixed objects in the sky (actually they all do have their own motions) we could use Zubenelgenubi as a means of comparing the relative speeds of these objects.

Click on picture to see it full size.

Click on picture to see it full size.

   What would really add to this conjunction would be to have the crescent Moon as part of it as was the situation on the evening of 1 December 2008 when the waxing crescent Moon, Venus, and Jupiter joined for a triple conjunction. This was taken with my older 6 megapixel Canon Powershot Camera on a tripod with the aperture set to F8; shutter speed to 1-second, and ISO was on automatic.

   Click here to go to the Qué tal in the Current Skies web site for more observing information for this month.

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