Mercury at Eastern Elongation

orbital-positions    On Thursday October 1st Mercury, the innermost planet, will reach its orbital position known as greatest eastern 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 – from superior conjunction, behind the Sun, out to the left (east) from the Sun to eastern elongation, then reverse and move westward through (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 planet Mercury is currently over the western horizon at sunset local time and will remain visible for most of the month.

   
   
   

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Saturn Corrects Its Reversal

   On Tuesday September 29th in a move that comes about annually, Saturn will once again reverse its direction from moving toward the west to moving toward the east.
   Since around May 11th Saturn 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 Saturn. This apparent westward motion of Saturn is known as retrograde motion and for Saturn it’s retrograde motion comes to an end during mid-September when Saturn resumes its normal orbital motion toward the east, or to the left as we view Saturn 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 Saturn 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 Saturn orbits the Sun to the east as we see it from Earth.

   Saturn is located over the southern horizon after sunset local time. It is about 7-8o to the east from Jupiter.

   
   
   
   

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Moon – Jupiter & Saturn Conjunctions

   The waxing gibbous Moon, over the next two evenings (September 24th and 25th, will pass by two of the giant outer planets. The Moon will pass within about 2-3o from Jupiter and about 1-2o from Saturn.
   Off toward the eastern horizon is the innermost planet Mercury and the bluish-white star Spica in Virgo the Harvest Maiden.


   
   
   

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September Moon at Descending Node

   Wednesday September 23rd the 7-day old first quarter Moon crosses 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 date of the descending node the first quarter Moon will be about 20o to the east from the heart of Scorpius the Scorpion, the reddish star Antares, and about 15-16o west from Jupiter.
   Mercury and Spica are still a couple of degrees apart but low above the horizon as the Sun is setting.

   
   
   
   
   

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Mercury- Spica & Moon – Antares

   Tuesday September 22nd shortly after sunset local time look toward the western horizon for the innermost planet Mercury to be about 1o from the bluish-white star Spica in Virgo the Harvest Maiden. The two should make for an interesting comparison in apparent magnitudes with Spica at 0.96 and Mercury with a -0.01 apparent magnitude.
   The nearly first quarter but still waxing crescent Moon will be about 7-8o from the reddish star Antares in Scorpius the Scorpion. Both are positioned over the southern horizon.

   
   
   

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Last Night Had It’s Hang-ups!

   Last evening was another opportunity to image the ISS as it passed over my part of the world. So I did!
   While out in the backyard I aimed my camera nearly straight up to get a picture of one of my favorite parts of the sky. This is near the star Altair in the constellation Aquila the Eagle. Near Altair is the ‘tiny’ constellation of Delphinus the Dolphin. Looking further upward from the kite or diamond-shape stars there is another smaller constellation, Sagitta the Arrow.
   If you find Sagitta use the two stars at the end as ‘pointer stars’ and they will direct your eyes to a neat little star cluster, Brocchi’s Custer, also known as the Coathanger Cluster.

   
   
   

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September Moon at Perigee

   Our Moon reaches perigee, (closest to Earth), for this orbit, on Friday September 18st. At that time the Moon will be at a distance of 28.15 Earth diameters, 223,122 miles (359,081 km) from the Earth.

   On the day of the perigee Moon the 1.5-day old waxing crescent Moon will be over the western horizon near the innermost planet Mercury. Further to the east are 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)

   
   
   
   
   
   

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Sun Enters Virgo-2020

view_from_earth   Wednesday September 16th the Sun in its apparent eastward motion along the ecliptic, moves out of the constellation of Leo the Lion and into the constellation of Virgo the Harvest Maiden. This is the true or actual position of the Sun as opposed to the pseudoscience of astrology which usually has the astrological Sun one constellation ahead or east from the Astronomical Sun’s position.
   In a few days the Sun, according to astrology, will cross the ecliptic moving southward crossing from Virgo into the constellation of Libra the Scales. We know this day as the September equinox, which this year is on the 22nd.

   Read a little more about how astrology has the Sun incorrectly placed in a previous blog, and in another blog discussing the effects of precession.

   
   
   

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Moon-Venus Conjunction + M44

   Monday morning September 14th look eastward in the pre-dawn skies for the 26-day old waning crescent Moon to be about 4-5o from the planet Venus and about the same distance from the open star cluster M-44, the Beehive Custer.

   The trio should make for an interesting view with binoculars.
   
   
   
   
   
   

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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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