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September 2019 Skies

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September Skies

by Dick Cookman



Highlights: Comet Journal, Martian Landers, Meteor Showers, Autumnal Equinox, Planet Plotting, September Moon

Focus Constellations: Bootes, Corona Borealis, Ophiuchus, Hercules, Lyra, Aquila, Cygnus, Pegasus, Andromeda, Perseus, Camelopardalis, Ursa Major, Draco, Ursa Minor, Cepheus, Cassiopeia

Comet Journals

C/2018 W2 (Africano) is moving southward through Perseus, Andromeda, and Pegasus in September. It is at perihelion on September 5, 2019, and is closest to Earth on the 27th when it may reach 8th magnitude.

C/2018 N2 (ASASSN) is an 11th magnitude comet moving from Triangulum into Andromeda in September. It rises in early evening skies and slowly moves through northern skies for the next two years. It reaches perihelion on November 11 in Andromeda and probably will not exceed 10th magnitude as it moves perpendicular to the plane of the solar system between Mars and Jupiter.

Comet 260P/McNaught is an 11 to 12th magnitude comet. It moves northward from Aries into Perseus in September, passes closest to Earth on October 4, and is at perihelion on the 8th.

Comet C/2017 T2 PanSTARRS is in Taurus at magnitude 12. It will be closest to Earth on December 29 and reaches perihelion in May 2020.

Mars Landers

The Insight lander continues to monitor atmospheric conditions at its Martian landing site on Elysium Planita and tracking tremors associated with marsquakes. The mole carrying the Heat Flow and Physics Properties Package (HP3) is still stuck at a depth of 30 centimeters, possibly due to an obstruction or other issues. On June 28, InSight’s robotic arm, designed to place instruments onto the Martian surface, lifted the support structure for the HP3 and uncovered the mole as part of efforts to troubleshoot the instrument. The science team and the German manufacturer are continuing testing on Earth to develop procedures to free the instrument, drill deeper, and proceed with heat flow measurements.

The Curiosity rover is in Glen Torridon, the clay-bearing unit in the valley adjacent to Vera Rubin Ridge on 16,404 foot Mt. Sharp at the center of Gale Crater. After drilling into the smooth clay bearing rock unit at Aberlady in April, the rover spent most of June and July moving southward through Glen Torridon, examining pebbles and rocks, rippled sand, and ridges with bedrock layers at the surface of the clay-bearing unit. After investigating Harlaw Ridge in early July, Curiosity analyzed rock exposures in the northern half of Glen Torridon as it moved toward the Southern Outcrop which is the north facing escarpment of an elevated area of exposed, fractured bedrock called the Visionarium. After successfully ascending the 21° slope at the end of July, the search for the next drill site ensued. On August 1, after thorough geochemical analysis of the area, the go-ahead was declared for drilling at Glen Etive 1. By the 5th, the rover completed drilling of the 22nd sample on Mars in the 7 years since arrival. After sample preparation, the drilling powder was delivered to SAM for gas chromatograph and mass spectrometer analysis on Sol 2500 (8/16/19). The balance of August was devoted to preparation for the solar conjunction of Mars of 9/2/19 when Mars will be on the opposite side of the Sun and out of radio communication with Earth for two weeks.

The elevated levels of atmospheric methane discovered by Curiosity in June contrast with levels measured by the ExoMars Trace Gas Orbiter which measures levels 8 times lower. Analysis by a group led by John Moores, York University Research Chair in Space Exploration, was published in the Geophysical Research Letters. It hypothesizes that a small amount of methane (the primary constituent of natural gas) constantly seeps out of the ground on Mars. Limited convection at night allows a build up in the atmosphere near the ground and vigorous convection caused by solar heating during the day rapidly mixes and dilutes the atmosphere, producing the much lower levels recorded by ExoMars.

Meteor Showers, Asteroid Surprises

September meteors are few and far between. The Aurigids are relatively minor showers appearing in the 1st third of September with little interference from the waxing crescent and 1st quarter Moon.

  • September 1: Alpha Aurigids. Active Aug. 25-Sep. 5. Radiant 5h36m +42°. ZHR 10. 66 km/sec. Waxing Crescent Moon. Progenitor: Comet Keiss.
  • September 8: Delta Aurigids Active Sep. 5-Oct 10. Radiant 4h00m +47°. ZHR 6. 64 km/sec. Waxing Gibbous Moon. Progenitor: Comet Keiss.
  • September 20: Piscids. Active Sep. 3-Oct. 2. Radiant 0h20m -01°. ZHR 3. 36 km/sec. Waning Gibbous Moon. Progenitor: Comet Wirtanen?

Asteroid 2019 QQ3 passed within 50,000 miles of Earth at 20 miles/sec on August 26. It was about 5 meters in diameter.

Autumnal Equinox

The term “equinox” for the day when the hours of night and day are equal, is derived from Nox, the Roman Goddess of Night. At 3:50AM EDT on September 23, Earth’s axis is perpendicular to a line between Earth and Sun and leans 23.5° toward its direction of orbital travel. In this position, all places on Earth have almost, but not quite, 12 hours each of sunlight and darkness. The inequality of night and day isn’t due to a quirky goddess. Rather it is due to the timing of sunrise and sunset which is influenced by latitude, period of time required for all of the Sun to appear or disappear, and atmospheric light refraction. The latter two delay sunset and cause earlier sunrises, lengthening daytime hours. Low latitudes experience the equinox later than high latitudes. Fall equinoxes are delayed until October in equatorial regions.

Northern and southern auroral light displays which are slightly more frequent during equinox seasons are rare this year due to sunspot absence during the current low in the 9 to 11 year sunspot cycle. The last peak in 2014 was for Cycle 24 when sunspots observed reached levels of 140. The previous peaks (Cycle 23 and 22) were in 2000 and 1988-1989 when levels exceeded 200. Previous recent sunspot minimums include 2008-2009, 1996-1997, and 1986-1987.

Planet Plotting

September morning planets are limited to dim Uranus (+5.7) in Aries, and dimmer Neptune (+7.8) in Aquarius. The former rises in the early evening and sets after sunrise and the latter is visible all night long, reaching opposition with the Sun on the 10th. Jupiter (-2.1 to -1.9) in Ophiuchus and Saturn (+0.3 to +0.5) in Sagittarius rise after the Sun and set in the later part of the evening. Mercury (-1.7 to -0.2 ), Venus (-3.8), and Mars (+1.7 to +1.8) in Leo and Virgo are lost in the Sun’s glare in September with the 1st two appearing in the evening twilight slightly after sunset at the month’s end, and Mars is lost in the glow of the sun throughout the month. Mars and Mercury are in conjunction with the Sun on the 2nd and 3rd respectively. Mercury will appear to visit within less than 1° from Mars and Venus on the 3rd and 13th respectively.

The waxing gibbous Moon is 2.0° from Jupiter at 3:00AM EDT on the 6th, 0.04° from Saturn at 10:00AM EDT on the 8th, and 4° from Neptune at 2:00PM EDT on the 13th. The waning gibbous Moon is 4.0° from Uranus at 4:00PM EDT on the 17th. The waning crescent Moon is 3.8° from Mars at 1:00AM EDT on the 28th, and the waxing crescent Moon is 4.0° from Venus at 2:00PM EDT and 6.0° from Mercury at 6:00PM EDT on the 29th.

PlanetConstellation(s)MagnitudePlanet PassagesTime, Date
SunLeo, Virgo-26.8New Moon2:26PM EDT, 9/28
MercuryLeo, Virgo-1.7 to -0.2Superior Conjunction
Mars, 0.64°SSW
Venus, 0.29°NNE
10:00PM EDT, 9/3
1:00PM EDT, 9/3
10:00AM EDT, 9/13
VenusLeo, Virgo-3.8Mercury, 0.29°SSW10:00AM EDT, 9/13
MarsLeo, Virgo+1.7 to +1.8Solar Conjunction
Mercury, 0.64°NNE
7:00AM EDT, 9/2
1:00PM EDT, 9/3
JupiterOphiuchus-2.1 to -1.9  
SaturnSagittarius+0.3 to +0.5  
NeptuneAquarius+7.8Opposition3:00AM EDT, 9/10

September Moon

The New Moon of September on the 28th at 2:26PM EDT is the beginning of Lunation 1197 which ends 29.36 days later with October’s New Moon on the 27th at 11:39PM EDT. The September Full Moon is on the 14th at 12:34AM EDT. It is known as the “Fruit Moon, or Harvest Moon”. Colonial American farmers took advantage of its light to continue harvesting long after sunset. Like most full moons, the “Harvest Moon” rises at sunset, but near the Equinox it rises near sunset for many nights in a row because moonrise advances only 30 minutes a day in contrast to the normal 50 minutes a day. Celts called it the “Singing Moon” and it was named the “Barley Moon” in Medieval England. Chinese call it the “Chrysanthemum Moon” and the Anishinaabe (Odawa and Ojibwe) people recognize it as “Waatebagaa-giizis” (Leaves Turning Moon.)

Lunar Apogee (maximum orbital distance) occurs on the 13th at 9:00AM EDT when the Moon is at 252,511 miles (63.71 Earth radii). Perigee occurs on the 27th at 10:29PM when the Moon is at a distance of 222,328 miles (56.10 Earth radii).

PlanetConstellationMagnitudeMoon PassagesMoon Phase, Moon Age
SunVirgo-26.82:26PM EDT, 9/28New..0 days
MercuryVirgo-0.26.0°N, 6:00PM EDT, 9/29Waxing Crescent..1.15 days
VenusVirgo-3.84.0°NNE, 2:00PM EDT, 9/29Waxing Crescent..0.98 days
MarsVirgo+1.83.8°NNE, 1:00AM EDT, 9/28Waning Crescent..29.31 days
JupiterOphiuchus-1.92.0°N, 3:00AM EDT, 9/6Waxing Gibbous..6.85 days
SaturnSagittarius+0.50.04°S, 10:00AM EDT, 9/8Waxing Gibbous..9.14 days
UranusAries+5.74.0°S, 4:00PM EDT, 9/17Waning Gibbous..18.39 days
NeptuneAquarius+7.84.0°S, 2:00PM EDT, 9/13Waxing Gibbous..14.31 days

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