About Bob Riddle

Currently: Retired from the physical classroom (May 2017) but not yet finished learning and teaching. Column Editor, Scope on the Skies - Science Scope Magazine; NASA/JPL Solar System Educator Program - Solar System Ambassador Program, and Solar System Ambassadors Program.

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.

   
   
   
   
   

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.


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The September Equinox of 2020: BTW, The Sun Is Not In Libra

   On Tuesday September 22nd at 13:32 UT, (8:32 am CDT) the Sun will have reached the astronomical coordinates of 0 degrees declination and 12 hours of right ascension, or RA. This places the Sun within the boundaries of the constellation Virgo the Maiden, or as some would say, “the Sun is in Virgo.” This is the actual position of the Astronomical Sun as opposed to the pseudoscience of astrology which has the astrological Sun entering the constellation of Libra the Scales.
   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.
   Declination is the astronomical equivalent to latitude measuring from 0 degrees at the equator to 90 degrees at either pole. Right ascension, or RA, is like longitude except that there is only east RA. The globe is divided into 24 sections, and like meridians of longitude, these hour circles are 15 degrees wide at the celestial equator and taper to a ‘point’ at the north and south pole respectively. In RA the ‘hour’ circles are counted from 0 hours to 23 hours. The 0 hour circle is at the intersection of the ecliptic and the celestial equator in the constellation of Pisces the Fishes.
   In a class lesson about seasons today would be one of the two days during the year when the Sun would be described as being over the Earth’s equator. If you were at the Earth’s equator the Sun would have an altitude of 90 degrees, or straight up in your sky at your local time for midday. At that moment there would not be a shadow. However at any other latitude, north or south at midday, the Sun would be at an angle less than 90 degrees and there would be a midday shadow. (Midday is the local time when the Sun is halfway between local rising time and local setting time. At any midday the Sun is at its maximum altitude above the southern horizon in the northern hemisphere, or is at its maximum altitude above the northern horizon in the southern hemisphere.)
   What is often noted about an equinox day is the reminder that equinox means equal night as a reference to there being equal amounts of daylight, and night. Also on an equinox day the Sun would rise due east and set due west for virtually everywhere on the globe. The times for sunrise and sunset would be approximately 12 hours apart, and the rising time would be around 6 am local time, and the setting time would be around 6 pm local time.

Hola Moon doh

Hola ‘Moo’ndo! Think Globally.

   So why “September Equinox” instead of using the more familiar “Fall Equinox”. Primarily because the southern hemisphere is also changing seasons on this day however for the southern hemisphere this is the start of their spring season. Despite the opposite seasons it is somewhat of a northern hemisphere bias that traditionally we would call this day the “Autumnal or Fall Equinox”, and in March we would say the “Spring” or “Vernal Equinox”. I favor the use of the name of the month so that regardless of which hemisphere it is just simply the March equinox or the September equinox, and by extension we would also have the June solstice and the December solstice..
   
   This short video shows students at Colegio Menor San Francisco de Quito, a school in Quito Ecuador, measuring the altitude of the sun hourly on the day of the 2004 September Equinox. They were taking part in Project SunShIP, Sun Shadow Investigation Project. There are also some pictures showing a local midday shadow from other participating schools in the United States and U.K.

   
   
   

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.


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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.

   
   
   

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.


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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.

   
   
   

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.


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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)

   
   
   
   
   
   

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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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.

   
   
   

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.


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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.
   
   
   
   
   
   

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.


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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.

   
   
   
   

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.


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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.

   
   
   

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.


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