Dance of the Planets

23 May to 11 June - 8:30 pm CDT

23 May to 11 June – 8:30 pm CDT

   In my posting yesterday I described the orbital motions of these three planets without the use of a graphic to help visualize that explanation. This animated graphic that is set to one-day intervals starts with today’s date and then runs for a few weeks. This gives enough time to see how both Mercury and Venus are moving eastward while it appears that Jupiter is moving in the opposite direction, west towards the Sun. Jupiter is in fact moving eastward but considerably slower than the Sun’s apparent eastward motion. The net effect is that Jupiter sets earlier and earlier as the Sun gets closer, and eventually Jupiter moves behind the Sun.

   Both Mercury and Venus were recently on the opposite side of the Sun from the Earth at superior conjunction. Coming from that relative position both planets travel eastward until they reach a point with respect to the Sun that we see as the furthest apart, or the greatest angular separation between the Sun and Mercury or Venus. This happens on either side of the Sun and are known as elongations. Since both planets are on the east side of the Sun they are both heading toward eastern elongation. In the animated graphic above you can see all of Mercury’s orbit on the east side of the Sun including the part where Mercury reaches eastern elongation and heads back toward the Sun. Because Venus is further from the sun it has a longer orbital period around the sun and likewise a longer orbital path so Venus’s orbital path on the graphic extends past the edge.


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

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