Venus Reaches Western Elongation

inner-planets-positions   Sunday January 6th 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 the planet Jupiter, about 13o below Venus, east from Venus. The reddish star Antares in Scorpius the Scorpion is also about 13o from Venus, and is about 6o from Jupiter. If the skies are dark enough the Milky Way should be visible rising toward the southwest.

   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 latest time in this orbit. On the day of the western elongation Venus will be 46.9o 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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Mercury at Western Elongation

   On Saturday December 15th Mercury, the innermost planet, will reach its orbital position known as greatest western elongation at 21.3o. At that moment Mercury, the Sun, and the Earth, would be arranged in something close to approximating a right angle as this graphic shows. Even though it sounds confusing at western elongation for either Mercury or Venus the inner planet will be to the right of the Sun as we view them, meaning that at western elongation an inner planet rises in the east before the Sun rises. And at eastern elongation with the inner planet on the left side of the Sun the inner planet follows the Sun across the sky setting after the Sun sets.

   From our perspective the orbits of Mercury and Venus appear to move from one side of the Sun to the other – out to the left (east) from the Sun to eastern elongation, then reverse and move westward (inferior conjunction) between the Earth and the Sun to western elongation. From there the inner planet moves eastward going behind the Sun (superior conjunction) and eventually reappearing on the eastern side of the Sun for an eastern elongation. Repeat over and over – do not stop!


   Mercury is visible in the morning skies just before sunrise local time, as this graphic shows. Venus, to the west from Mercury rises about 2 hours before Mercury, and Jupiter rises shortly after Mercury.

   
   
   
   
   

Click here to go to the Qué tal in the Current Skies web site for monthly observing information, or here to return to bobs-spaces.


Also Follow me and other great resources at Feedspot.

Venus at Western Elongation

inner-planets-positions   Saturday June 3rd 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.

   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 latest time in this orbit. On the day of the western elongation Venus will be 45.9o 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.

   
   
   
Caution: Objects viewed with an optical aid are further than they appear.
   Click here to go to the Qué tal in the Current Skies web site for more observing information for this month.

Backfield in Motion

   This animated graphic shows the morning sky at 5 am CDT facing toward the east. It is set to 1-day per image starting with yesterday the 14th and ending on the 20th. If you watch the animation for a while you will see the two planets are lower above the horizon as each day passes. Additionally you should notice the stars are higher as each day passes. So what is going on?
merc-venus-ani
   The animated graphic is simulating the orbital motions of the two planets as they are both moving toward the east. The animated graphic is also showing the effect the Earth’s motion on sky, and even the Sun although it is still below the horizon. orbital-positions
   As inner planets, Mercury and Venus orbit the Sun faster than the Earth. Each day Mercury moves approximately 4o, Venus moves approximately 1.6o each day, and the Earth moves approximately 1o daily. Which in turn means that the sun has an apparent eastward motion the same as the Earth’s 1o daily. The net result is that when either of the inner planets moves eastward they are traveling eastward faster than the Sun and will eventually catch up with and pass by the Sun as they move through superior conjunction to eastern elongation. Mercury moving much more quickly than Venus.
   The motion of the sky, like the Sun, is an apparent motion caused by both Earth rotation and revolution. Obviously as the Earth rotates toward the east celestial objects appear to rise in the east and move toward setting in the west. As time passes during the day and night celestial objects will have traveled 360o. star-aniRevolution also causes an apparent westward motion of the sky but each day, since the Earth only moves about 1o, the sky likewise only appears to move about 1o each day. This translates into celestial objects rising approximately 4 minutes earlier each day, or about 2 hours earlier each month. In terms of daily observing if you watch the same object at the same time each day that object will be slightly further to the west, and higher above the horizon as this animated graphic shows.
   
   
   
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Caution: Objects viewed with an optical aid are further than they appear.
   Click here to go to the Qué tal in the Current Skies web site for more observing information for this month.

Mercury at Western Elongation

orbital-positions   On Saturday 12 July Mercury, the innermost planet, will reach its orbital position known as greatest western elongation. At that moment Mercury, the Sun, and the Earth, would be arranged in something close to approximating a right angle as this graphic shows.
   From our perspective the orbits of Mercury and Venus appear to move from one side of the Sun to the other – out to the left (east) from the Sun to eastern elongation, then reverse and move westward (inferior conjunction) between the Earth and the Sun to western elongation. From there the inner planet moves eastward going behind the Sun (superior conjunction) and eventually reappearing on the eastern side of the Sun for an eastern elongation. Repeat over and over – do not stop!
   The banner graphic at top of page shows the orbits of both inner planets with planets where they will be on the 12th. Mercury is at western elongation while Venus is past its own western elongation and is currently moving eastward toward the Sun and superior conjunction in a few months (October).
   Mercury is currently visible as an ‘morning star’ over the eastern horizon at sunrise.

   
   
   
Caution: Objects viewed with an optical aid are further than they appear.
   Click here to go to the Qué tal in the Current Skies web site for more observing information for this month.

The Elongated Mercury

   This evening the waxing crescent Moon and three planets will be above the western horizon at sunset, however depending on your latitude and shape of your local horizon Mercury and Saturn may be a challenge to see. Adding to that is at the time of sunset the sky is still too bright to see these planets with the naked eye. And by the time the sky darkens enough, maybe another 20 minutes or so, Mercury and Saturn may have already set.

Mercury at Elongation

9 October: Mercury at Greatest Eastern Elongation

   The Planet Mercury has reached the point in its orbit around the Sun where it is at its maximum angle out from the Sun as we see the two of them from here on Earth. This is known as an elongation. Since Mercury is currently on the left or east side of the Sun it is an ‘evening planet’ setting after the Sun, and today it is at its Greatest Eastern Elongation.
   Not one to stop, Mercury continues moving until reaching greatest western elongation at the end of next month. Until then the innermost planet will be moving in retrograde or toward the west. As Mercury moves west at the rate of about 4 degrees each day the Sun in its apparent motion toward the east is moving about 1 degree each day. So in less than a month, on 1 November, Mercury will have reached inferior conjunction, between the Sun and Earth.

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

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.