July Moon at Descending Node

   Wednesday July 12th the 18-day old waning gibbous Moon will be crossing the plane of the ecliptic moving south. This is known as the descending node, one of two intersections the Moon’s orbital path (dark green line) has with the ecliptic.
   

   On the day of the node crossing the 18-day old waning gibbous Moon will be over the south-southeast horizon an hour or so after sunset local time. The Moon will be in conjunction, and within about 2o from the outermost, (8th), planet Neptune.
   
   
   
   

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

Neptune Backs Up

Two days in a row! Like the song goes, “slow down you move too fast” – or proofread!!
   Friday June 16th the outermost of the 8 planets, Neptune, ends its westward retrograde motion around the Sun and will resume direct motion, moving eastward will come to an apparent halt in its eastward or direct motion and appear to start moving backward to the west in what is known as retrograde motion. In this graphic the location of the 21.5-day old waning gibbous Moon is shown to be about 2-3o from Neptune. Neptune has an apparent magnitude of nearly 8.0 making it all but only visible with telescopes – and certainly not on this date with -12th magnitude Moon nearby.

   Retrograde motion is an apparent motion that the outer planets, relative to the Earth, have. It is an apparent motion that looks as if the outer planet stops it normal direct motion to the east and reverses direction to the west. After a period of time the apparent westward motion ends and the planet resumes its normal orbital path to the east. Retrograde motion happens as the faster moving Earth catches up with and then passes by the outer planet. It is during this time that the backward apparent motion happens.

   The two inner planets also have retrograde motion but it is a result of their orbit around the Sun and not the Earth passing them by. For approximately one-half of their orbit they move east, from western elongation through superior conjunction to eastern elongation. Then at eastern elongation the inner planet starts moving westward through inferior conjunction to western elongation.

   Read a little more about retrograde motion in my February 2012 Scope on the Skies column, drawkcab planets, in Science Scope Magazine.

   
   
   

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.

Neptune at Western Quadrature

orbital-positions   On Sunday June 4th the position of the planet Neptune with respect to the Earth and the Sun places this ringed planet at what is called western quadrature. At that orbital position Neptune, and actually any outer planet, is at a 90 degree angle from us as this graphic shows. Think third quarter Moon as that is a fair comparison of the relative positions. At this position Neptune leads the Sun across the sky from east to west as the Earth is rotating, meaning that Neptune rises before the Sun and also sets before the Sun.

click on graphic to see it larger   Neptune currently is within the boundaries of the constellation Aquarius the Water Bearer. At around 7th magnitude Neptune is too dim to see with the naked-eye but easily seen with a telescope or binoculars. In 7×50 binoculars Neptune may be visible near the 4th magnitude Lambda Aquarii, and just below the point of a small triangle arrangement of 6th magnitude stars.

   This is a short video clip from a much longer video that I made as part of a live musical performance called “Orbit” at the Gottleib Planetarium in Kansas City Missouri during May 2011.

   
   
   

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

Neptune at Solar Conjunction

view-from-earth_neptune-solar-conjunction   Thursday March 2nd the outer planet Neptune reaches a point in its orbit where it passes behind the Sun as we view this from Earth. Neptune, and the other outer planets, dwarf planets, or small solar system bodies, all eventually reach this position on the opposite side of the Sun known as solar 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.

Moon Moons Uranus

   Thursday January 5th the just past first quarter Moon, a waxing gibbous Moon, is close to the outer planet Uranus, and also two of the Dwarf Planets. But close only in the sense that the three are in the same direction, or line of sight. Uranus as the next-to-last outermost of the 8 planets is 19.8 Au and has an apparent magnitude of 5.8. Ceres and Eris, while both are Dwarf Planets, are at very nearly the opposite ends of the solar system. Ceres is within the asteroid belts at a distance of 2.5 AU and has an apparent magnitude of 7.64. Eris, on the other hand is 96 AU from the Earth and has an apparent magnitude of 18.6.

   
   
   

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.

Mars and Neptune Conjunction, inlcuding the Moon and Venus


   A previous post described the daily motion of Mars as it moves toward the planet Neptune. Well Monday evening January 2nd the planets Mars and Neptune, and our Moon (a 5-day old waxing crescent Moon) will all fit within the field of view of binoculars with Mars and Neptune separated by about 1.5o.

   In that post I had also mentioned that were Neptune observed from the surface of Mars then Neptune would be starting its retrograde motion. Actually I was not entirely correct as I was basing this on how the two planets looked from Earth rather than Neptune as seen from Mars. Compare the distance between the Earth and Mars and the difference between the orbital speed of the two planets. Then consider Mars and Neptune where there is a greater difference between the orbital speeds of Mars and Neptune as well as the distance between the Mars and Neptune then there is between the Earth and Mars.

   What this means is that Neptune, as viewed from Mars, will not actually begin to retrograde until around the middle of June.

   
   
   

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.

Mars Moves Into the New Year

   Over the next several days Mars will catch up with and then pass by Neptune coming within less than 0.5o on December 31st. Mars moves at a daily rate of about 0.5o while Neptune moves about 0.006o each day. If you were on Mars observing Neptune you would see Neptune begin its retrograde motion. Interestingly from here on Earth Neptune has just ended its retrograde motion. It’s all relative as somebody probably said.
   Both planets will be above the southwestern at sunset local time with only Mars being visible without the use of an optical aid.
   Comet 45P/Honda-Mrkos-Pajdušáková may be bright enough to be visible with binoculars and certainly with a telescope, and definitely should make for an interesting picture with the waxing crescent Moon nearby.
   
   
   
   

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.