Mercury Ends Retrograde Motion

   
mars-retrograde-ani   When the Earth’s orbital speed is compared to an outer planet there will be a time period when the faster moving Earth passes the outer planet. This sets up a temporary illusion where it appears as if the outer planet has reversed direction and is now moving backward toward the west, or in retrograde motion.
   On the other hand the two inner planets, Mercury and Venus, also revolve around the sun toward the east and go through a period of retrograde motion. However theirs is not as a result of the Earth’s faster orbital speed but rather it is their faster orbital speed compared with the Earth’s that gives them their retrograde motion. And unlike the apparent retrograde motion for an outer planet, Mercury and Venus do actually move in retrograde motion as this animated graphic is showing.
   So, on Saturday December 23rd the innermost planet, Mercury, ends its retrograde motion for this particular orbit and resumes its eastward motion. In the animated graphic the size for Mercury is exaggerated and the animation is set to a 1-day interval. It is showing Mercury moving westward as Venus is moving eastward. As Mercury moves along its orbit it eventually curves around and starts moving toward the east. This may be close to the day when Mercury reaches its furthest separation from the Sun on the west or right side of the Sun. That point is known as Greatest Western Elongation and is on January 1st. The counterpoint to this is when Mercury, or Venus, reaches their respective Greatest Eastern Elongation on the left or east side of the Sun.

   
   
   
   

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 Backs Up

   The giant outer planet Jupiter slows down and reverses its orbital motion on Friday January 8th as it begins its more or less annual retrograde motion. Retrograde motion is an apparent motion that occurs for an outer planet (past Earth’s orbit) when the faster moving Earth catches up with and then passes by the outer planet. During this retrograde motion Jupiter will move westward near the stars of Leo the Lion.
   Jupiter currently rises about an hour before midnight local time and is very visible above the southwestern horizon 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.

Uranus is Stationary

   I suppose if you are into twerking then the title of this posting should cause a pause. However.
    All planets orbit the Sun and relative to Earth’s orbit the direction is to the east. Each planet periodically appears to go backward to the west, or in retrograde motion. The outer planets appear to retrograde but it is an illusion created by the faster moving Earth as it passes the outer planet. The two inner planets, on the other hand (or orbit) do actually move westward as they orbit from eastern elongation to western elongation. At the transition between regular or direct motion and retrograde motion, and the transition from retrograde back to direct motion the planet appears to pause in its orbital motion. This apparent pause is referred to as when the planet is stationary.
   Retrograde motion of an outer planet like Uranus will vary in the duration. Uranus began its retrograde motion on July 26th and ends that apparent motion and resumes its east, direct, or prograde motion on December 26th. The animated graphic shows the orbital motion of Uranus during most of 2015 including its retrograde motion. The graphic is based on an Atlas view of the sky and like any map shows some of the coordinate lines. The stars are part of the constellation Pisces the Fishes. The green line is the ecliptic, the blue line is part of the constellation shape pattern..
   
   
   
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.

Mars Ends Retrograde Motion

Click on graphic to see it full size.

Click on graphic to see it full size.

   Since the first of this past March the ‘red planet’ (love saying that!!) Mars has been moving in retrograde near the star Spica in Virgo. Retrograde, or retrograde motion, is an apparent reversal of an outer planet or dwarf planet’s regular orbital motion eastward around the Sun – as viewed from Earth. On Wednesday 21 May Mars ends its retrograde motion and resumes its regular or direct motion (eastward). Mars is also recently past opposition in April and so it is still near its maximum apparent magnitude (brightness) of -0.75. Nearby, for comparison, is the 3rd magnitude star Porrima.
Read more about the retrograde motion of Mars in a previous blog.

   
   
   
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.

Asteroids at Opposition

vesta-ceres-ani   Vesta, aka 4 Vesta, the third largest of the asteroids within the main asteroid belt between Mars and Jupiter reaches opposition Sunday 13 April. Two days later, 15 April, the closest Dwarf Planet to Earth, the former asteroid Ceres also reaches its opposition. Opposition is an arrangement with any outer planet or asteroid that is further from the Sun than the Earth. At opposition the Earth is between, in this case, either Vesta or Ceres, and the Sun. At opposition, like the full Moon, a planet or asteroid rises at sunset and is above the horizon all night and then sets at sunrise.

   Ceres, with an average diameter of 590 miles (950 km), as an asteroid was the largest and now as a dwarf planet is among the smallest if not the smallest object with enough mass to become round and thus qualify for a lateral promotion to dwarf planet status. Vesta has an average diameter of 525 km (326 miles ) and was the fourth asteroid discovered, in 1807. Vesta was also just recently visited and explored from orbit by NASA’s Dawn spacecraft. That spacecraft left orbit around Vesta in September 2012 and it is now heading for arrival at Ceres during the spring (northern hemisphere) of 2015. Vesta is also the brightest asteroid as seen from Earth and so the next few weeks offer an opportunity to perhaps see this asteroid and Ceres as they both move into and then past opposition and then moving in retrograde, westward.

Vesta and Ceres 10 April to 30 April.

Vesta and Ceres 10 April to 30 April.

   This animated graphic shows the westward motion of Vesta and Ceres as the two pass by several stars, some of which have a magnitude around Vetsa’s 5.39 and Ceres’s 6.5.

   Neither Ceres nor Vesta move fast enough to see any change in their position relative to any nearby ‘reference’ stars for at least a day or so. See if you can catch a ‘star’ changing its position relative to other stars by drawing a star chart of the stars you see in the field of view of your binoculars or telescope eyepiece. Repeat the drawing the next night, or wait another night. Do this a few times and by comparing your drawings you may find one of the dots you made for stars has shifted its position. That is the asteroid. Congratulations!

The Moon at 2 am CDT

The Moon at 2 am CDT

   Throughout this period the Moon will change from its waxing gibbous phase, pass through the Earth’s shadow for a total lunar eclipse, then begin its waning gibbous phases all the while passing past the asteroids Vesta, Ceres, Mars, Saturn, and a bunch of other celestial delights.

   
   
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 Pulls A Reversal

Jupiter Retrograde Motion: 7 November 2013-6 March 2014

Jupiter Retrograde Motion: 7 November 2013-6 March 2014

   Since 7 November 2013 the giant planet Jupiter has been moving westward, or at least it has appeared to be moving westward when in fact it has been in retrograde motion. This is an apparent motion that occurs for an outer planet when the faster moving Earth catches up and then passes by the outer planet. As has been previously and recently posted the planets Mars and Saturn have just begun their respective retrograde motions. Jupiter, today, reverses all of that as the angle between the Earth and Jupiter has increased to the point where Jupiter now is moving in its ‘correct’ direction, toward the east in what is called direct motion.
Click on graphic to see it full size.

Click on graphic to see it full size.

   Jupiter is currently very visible high overhead at local sunset time, and forms the point of a triangle with Pollux and Castor. This graphic shows the region of bright winter stars near Jupiter and the waxing crescent Moon.

   
   
   
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.