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.

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The 2014 MaRetrograde Motion

The 2014 Mars Retrograde Motion

   The ‘Red Planet’ Mars begins its retrograde Motion today. Retrograde motion is the apparent backward, or westward motion that a planet will appear to make at a regular point in its revolution around the Sun. We typically think of retrograde motion as being done by an outer planet from the Earth. This happens when the faster orbiting Earth catches up and passes by an outer planet. As this is happening the outer planet appears to slow down and then reverse its orbital direction toward the west. After a period of time (days to months) the outer planet again appears to slow down and then return to its regular eastward, or direct motion.
An inner planet orbit

An Inner Planet Orbit

   However the two inner planets Mercury and Venus also undergo retrograde motion. Approximately one-half of their respective orbits is eastward as is with all the other planets. This then brings the inner planets to what is know as eastern elongation in the evening skies. The other half of the orbit for Mercury and Venus is toward the west as they move from eastern elongation through inferior conjunction toward western elongation in the morning skies.

Coordinate Positions for Mars

 Date             RA	    Dec
  		 h  m  	  deg  m          
Feb  4		13 32	  -6 54
Feb 14		13 40	  -7 34
Feb 24  	13 45 	  -7 55
Mar  6  	13 45 	  -7 53
Mar 16  	13 41 	  -7 27
Mar 26  	13 32 	  -6 39
Apr  5  	13 19 	  -5 35
Apr 15  	13 04 	  -4 26
Apr 25  	12 51 	  -3 27
May  5  	12 40 	  -2 50
May 15  	12 35 	  -2 43
May 25  	12 34 	  -3 05
Jun 4  		12 38 	  -3 53
Jun 14  	12 46 	  -5 02
Jun 24  	12 57 	  -6 29

   
   
   
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.

Jupiter is Bi-Directional!

8 February to 10 March

8 February to 10 March

   The planet Jupiter is currently located within the boundaries of the constellation the Gemini Twins. Jupiter is also currently moving in retrograde – toward the west. Retrograde motion for an outer planet from the Earth happens when the faster orbiting Earth passes an outer planet. It is an illusion, or an apparent motion as all outer planets orbit toward the east, relative to the Earth. The animated graphic shows Jupiter daily at 8 pm CST and as you watch you can observe Jupiter’s retrograde motion by using the nearby 3rd magnitude star Mebsuta for reference. As the animated graphic advances there will be a frame (day) when retrograde motion for Jupiter ends and Jupiter returns to direct motion toward the east. That day is the 6th of March.

   
   
   
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.

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.

Not Pisces Today!

click on this image to see it full size

click on this graphic to see it full size

   According to the pseudoscience of astrology the Sun enters the constellation of Pisces the fishes today. However according to the real position of the Sun on this date the Sun is already within the boundaries of the constellation Aquarius the water bearer, (as shown in the banner graphic) the constellation to the west of Pisces. Based on the apparent motion of the Sun along the ecliptic path the Sun entered Aquarius two days ago on the 16th as shown in this graphic.
   Click here for a little more information about the difference between astrology and Astronomy and an effect caused by precession.
      
   Click here to go to the Qué tal in the Current Skies web site for more observing information.