Jupiter Corrects Its Reversal

jupiter-ani   On Saturday September 12th in a move that comes about annually, Jupiter will once again reverse its direction from moving toward the west to moving toward the east.
   For about the past 4 months Jupiter has appeared to be moving westward (toward the right) rather then toward the east. This happens as the faster moving Earth catches up with and then passes by Jupiter. This apparent westward motion of Jupiter is known as retrograde motion and for Jupiter it’s retrograde motion comes to an end on September 12th when Jupiter resumes its normal orbital motion toward the east, or to the left as we view Jupiter from the Earth.
   Since retrograde is a reference to motion and means backward or reverse motion, then the opposite of retrograde would be prograde motion. So it would be correct to describe Jupiter as having resumed prograde motion. However you would probably get a blank look from those you say this to! So stick with “direct motion” or just say that Jupiter orbits the Sun to the east as we see it from Earth.
   Jupiter is located over the southern horizon after sunset local time. It is about 7-8o to the west from Saturn.

   
   
   
   

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Neptune at Opposition – 2020

   Friday September 11th the outer planet Neptune reaches a position in its orbit around the Sun when it is on the opposite side of the Earth from the Sun. This coincidentally is known as opposition, and it is an orbital position which only the planets further from the Sun than the Earth may reach.
   At opposition an object orbiting the Sun beyond Earth’s orbit rises and sets in a fashion similar to our Moon when it is at full phase, in that the object at opposition rises at sunset and sets at sunrise.
   Currently Neptune rises at sunset and by late evening is over the southeastern horizon. Neptune has an apparent magnitude of 7.88 so it is beyond unaided-eye visibility but could be visible with large aperture telescopes or with a camera.

   
   
   

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September Moon at Ascending Node

   Wednesday September 10th the 22-day old last quarter Moon will be crossing the plane of the ecliptic moving north. This is known as the ascending node, one of two intersections the Moon’s orbital path has with the ecliptic. The ecliptic is actually the Earth’s orbit, and the Moon’s orbit is inclined about 6o from the ecliptic. So there are two node intersections, the ascending and descending nodes.
   On the morning of the node crossing the 22-day old last quarter crescent Moon will be to the east of the reddish star Aldebaran in Taurus the Bull. If you are a late night type watch for the Moon to rise around midnight local time giving you an opportunity to see Mars, Saturn and Jupiter arranged across the sky.

   On the other hand if you are like me and an early morning type then look for the Moon to be high above the southern horizon an hour or two before the Sun rises. Venus will be over the eastern horiozn and Mars over the southwestern horizon.

   Does our Moon actually go around the Earth as many graphics show? From our perspective on the Earth the Moon appears to circle around the Earth. However, in reality, the Moon orbits the Sun together with the Earth*
*Click here to read my 2006 Scope on the Sky column “The Real Shape of the Moon’s Orbit”. (PDF)
   
   
   
   
   
   
   

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The Red Object Tour: From Mars to Aldebaran


   Following a close encounter (conjunction) on September 5th-6th with the ‘Red Planet’ Mars our Moon will orbit eastward waning toward last quarter phase on September 9th. On the 9th the Moon will have a not as close encounter with another red celestial object. This being the reddish star Aldebaran, the ‘angry eye’ of Taurus the Bull.
   Aldebaran is at one of the open ends of the v-shaped open star cluster, the Hyades, the shape making up the Bull’s face.

   You can follow the Moon’s changing daily position with the graphic sequence below.
   
   
   
   
   
   
   
   


   
   
   

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Moon-Mars Conjunction

   Saturday evening September 5th watch for the 18-day old waning gibbous Moon to be very close, about 0.5-1o, from the planet Mars. Both objects are bright with Mars having a -1.93 apparent magnitude compared with the Moon’s much brighter -12.0 apparent magnitude.
   For another apparent magnitude comparison look west for the planets Jupiter (-2.52) and Saturn (0.33).

   The two, Mars and the Moon, should make for a striking combination with binoculars or low-power telescope eyepiece.

   
   
   

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Planetary Line-Up Ecliptic Style

   Look at the arrangement of the planets in the graphics below. One of the defining aspects of our solar system is the arrangement of the planets outward from the Sun. Not by size or distance but rather how their respective orbital paths around the Sun are all vertically arranged near the Earth’s orbital path, or as it is typically referred to as the Ecliptic or the Plane of the Ecliptic. The 8 classic planets all orbit the Sun with an orbital path that is up to about 8o from the ecliptic. This is called inclination. The table shows inclination relative the Earth’s orbit and also relative to the Sun’s center, its equator.
    Click on this link to read a previous posting (Tales Along the Ecliptic) about the ecliptic and inclination.
   During this week as the Moon moves eastward it will pass by the outer ringed planet Neptune Tuesday and Wednesday evenings September 1st and 2nd as the graphics show. However given the tremendous difference in apparent magnitude between the two (full Moon: -12.64 ; Neptune: 7.81) Neptune will not be visible, at least not while the Moon in nearby.


   Keep following the Moon as it orbits eastward toward the planet Mars when on September 5th Mars and the waning gibbous Moon will be less than 1o apart.
   
   
   

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Moon – Jupiter/Saturn Conjunctions

   Friday and Saturday evening August 28th and 29th the 9 to 10-day old waxing gibbous Moon will be passing by the outer planets Jupiter and Saturn. On Friday evening the Moon will be about 1-2o from Jupiter and by the same time Saturday evening the Moon will be about 6-7o from Saturn. On either of the evenings the Moon and a planet will fit within the field of view of binoculars.

   
   
   

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Moon on the Move

   Over the course of the next week or so the Moon will be moving eastward across the evening skies as it waxes from crescent toward full Phase on September 1st. This series of graphics shows the sky at 9:00 pm CDT daily until August 30th. Use the graphics as a guide to locating some of the stars near the path the Moon follows, as well as the evenings when the Moon is in conjunction with Jupiter, then Saturn.


   
   
   

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Virgo Grabs for a Croissant – or is it Crescent?

   Saturday August 22nd the 4-day old waxing crescent Moon will be about 4-5o from the bluish-white star Spica in the constellation Virgo the Harvest Maiden. Spica, from mythology, is described as the bundle of grasses (wheat, oats ?) in her hand – which is appropriate for something representing agriculture.
   Rising in the east is a pair of outer planets, Jupiter and Saturn.

   
   
   

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August Moon at Perigee

   Our Moon reaches perigee, (closest to Earth), for this orbit, on Friday August 21st. At that time the Moon will be at a distance of 28.50 Earth diameters, 225,868 miles (363,500 km) from the Earth.

   On the day of the perigee Moon the 3-day old waxing crescent Moon will be over the western horizon setting about 3 hours after the Sun sets. Rising over the eastern horizon are two of the giant outer planets, Jupiter and Saturn.

   Does our Moon actually go around the Earth as this graphic shows? From our perspective on the Earth the Moon appears to circle around the Earth. However, in reality, the Moon orbits the Sun together with the Earth*
   *Click here to read my 2006 Scope on the Sky column “The Real Shape of the Moon’s Orbit”. (PDF)

   
   
   
   
   
   

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.


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