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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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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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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Sun Is Not In Virgo

   According to the pseudoscience of astrology the Sun enters the constellation of Virgo the Harvest Maiden on Saturday August 22nd. When in fact the actual position of the Sun on this date is toward the west and still within the boundaries of the constellation of Leo the Lion.

   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 go to bobs-spaces.

Following the Arrows

   A few years ago one of my “Scope on the Skies” columns was about the Juno mission to Jupiter, but the focus was more or less about how the Juno spacecraft used solar power as far away as Jupiter, the Planetary Society and their Light Sail project, and a SciFi story by Isaac Asimov. However for me the most interesting part writing the column was learning about large concrete arrows scattered around our country. These turned out to be directional arrows used by pilots in the days of daytime flying and no radar for travel guidance. Arrows later had Beacons with lights, then radio signals were added. Eventually these were replaced with more advanced radios and radar.

   So we loaded the truck, gassed up, and drove from Lee’s Summit, MO southwest across Kansas to near the city of Haysville, KS to find the arrow near there. It was located along a dirt county road and nearly buried in grass and bushes. However the arrow was intact but whatever color it was painted had faded away.
      (37°32’04.7″N 97°25’11.9″W)

   Then we drove further south to near the Oklahoma, Kansas state line to the city of Anthony, KS. A couple of miles west from the city is the Anthony Airport and just off the road near the end of the runway is an Arrow and a Beacon.
      (37°09’06.8″N 98°04’37.0″W)

   Click here to download the ‘Scope’ column about the Arrows.

   
   
   
   
   
   


   
   
   

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Moon-Venus-M35 Conjunction

   Saturday morning August 15th the thin 25-day old waning crescent Moon will be about 2-3o from the inner planet Venus, and about 3-4o from the open star cluster M-35. All three are located near the feet of the Gemini Twins.
   The contrast in apparent magnitudes is very striking with the Moon shining at -10.7 compared to the -4.3 apparent magnitude of Venus. M-35, with an apparent magnitude of 5.3 will be difficult if not impossible to see with the bright Moon and Venus nearby. Under other conditions M-35 is visible to the naked-eye under dark skies. All three rise 2-3 hours before sunrise local time and will easily fit within the field of view of binoculars. To see just Venus and M-35 wait until tomorrow after the Moon has moved further east, is a thinner crescent and less bright. However Venus will have also moved a bit more than 1o east as it orbits along.
   If you can see the crescent Moon after sunrise it may even be possible to see Venus during the daytime using the Moon as a guide for where to look.

   
   

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Venus at Western Elongation

inner-planets-positions   Wednesday August 12th the inner planet Venus reaches the point in its orbit called greatest western elongation. As this graphic shows the inner planet Venus, or Mercury, is more or less at a right angle (90o) from the Sun and Earth at western elongation. From the surface of the Earth, your backyard, for example, Venus is to the right, or western side of the Sun and is rising before the Sun.

   On the day of the elongation Venus will be very visible over the southeastern horizon at or before sunrise local time. Venus is joined by a few other planets, Jupiter, Uranus, Mars, and Dwarf Planet Ceres. The waning crescent Moon is nearly straight overhead (at least from 40oN) and a few degrees from the open star cluster the Pleiades. In this graphic the orbital path of Venus has been added, and also an arrow to show the direction Venus will now be moving toward (eastward).

   At western elongation Venus, or for that matter Mercury the other inner planet, is as far out from the Sun as we see them and as a result Venus or Mercury will rise at the earliest time for this orbit. Locally Venus rises that morning at around 3:00 am CDT. On the day of the western elongation Venus will be 45.8o from the Sun. From western elongation forward Venus or Mercury will be moving eastward toward the Sun and each day rising closer and closer to the time of sunrise. As the planet moves eastward it is moving further away from the Earth toward superior conjunction on the opposite side of the Sun.


    As the distance between the Earth and Venus, or Mercury, increases combined with the decreasing angle between the planet, the Earth, and the Sun, Venus or Mercury decreases in apparent size and also waxes through gibbous phase shapes but we never see it at a full phase since that is at superior conjunction.

   
   
   

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Sun Enters Leo

10aug-view_from-earth
   Monday August 10th the Sun in its apparent eastward motion along the ecliptic, moves out of the constellation Cancer the Crab and into the constellation of Leo the Lion. 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.

   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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Mars as Big as the Full Moon! – No Way!!

A Martian Urban Legend
   “This year, during August, Mars will be at its closest to the Earth; so close, in fact, that it will appear as large as the full Moon.”
   Have you heard this urban legend before? Since 2003, emails describing this myth have circulated the internet usually during July or August. It all started during the opposition of August 2003 when Mars was about as close as it can ever be to the Earth (55,755,723 km – 34,645,000 miles) in a 20-year cycle of varying distances at opposition. Since then, usually around August, misinformation about the appearance of Mars circulates around the internet.

            Here Are Non-alternative Facts:

   This year, 2020, on Tuesday October 13th the outer planet Mars will be at opposition and 7 days (October 6th) after Mars is the closest to the Earth at 38,568,758 miles (62,070,399 km) – this time around. Coincidentally this is 3 months after Earth was at aphelion (July 4th. However this year is not the closest Mars has been from the Earth. The closest, so far, was during August 2003.

   In the time that it takes the Earth to catch up with and move into an opposition position, the outer planets have also been moving eastward relative to the stars in the background. Over time, the constellation where the outer planet is located during opposition and its retrograde loop gradually shift to the east. An opposition is also near the time when the distance between the Earth and an outer planet is around the minimum distance. Keep in mind that because the shape of the orbit is elliptical, this minimum distance will be different each time.

   However, there is an even more conclusive way to show that Mars could never be so close that it would appear as large as the Moon. To see how requires and some basic arithmetic using the numbers from a previous Mars opposition. You will see that Mars could not appear to be as large as our Moon unless some force somehow caused Mars to change its orbital position and literally move closer to Earth.

   On July 31st, Mars will be 57,595,180 km (35,787,986 miles) from Earth. Mars is 6,792 km (4,220 mi.) in diameter. The Moon is 3,475 km (2,159 mi.) in diameter and is an average 384,400 km (238,900 mi.) from Earth. In terms of apparent size our Moon has an angular diameter of 0.5o (30 arc minutes or 1800 arc seconds), while on July 31st Mars has an apparent diameter of 24 arc seconds.
    So with the following calculation using those values (24 / 1800) x 100% = 1.3%) Mars is only 1.3% the apparent size of our Moon.

   Another method to calculate how large Mars will appear as compared to the Moon:
   (Mars’s diameter ÷ Mars’s distance) ÷ (Moon’s diameter ÷ Moon’s distance)

         (4220 / 35787986) / (2159 / 238900) = 0.013 = 1.3%
    In other words, Mars on 31 July will be only 1.3% of the apparent size of the Moon.

   
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Uranus at Western Quadrature – 2020

   Sunday August 2nd the position of the planet Uranus, with respect to the Earth and the Sun, places this ringed planet at what is called western quadrature. At that orbital position Uranus, and actually any outer planet, is at a 90 degree angle from the Earth as this graphic shows, and also this graphic. Think third quarter Moon as that is a fair comparison of the relative positions of Earth, Sun, and Uranus.
    At western quadrature Uranus leads the Sun across the sky from east to west as the Earth is rotating, meaning that Uranus rises before the Sun and also sets before the Sun.

   
   
   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.

   
   
   

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