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September 2018 Skies

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September Skies

by Dick Cookman


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

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

Comet Journal

Comet 21P/Giacobini-Zinner (2018) moves from Auriga, through Taurus, and into Gemini in September. It is within 2° of Capella at the start of the month. It is approaching 7th magnitude and may reach naked eye visibility at 6th magnitude when near perihelion on September 10th. The comet has a bluish tail extending to the west visible through a small telescope at low (~50) power.

Comet C/2018 N1 (NEOWISE) spends most of September between Libra and Virgo. It reached magnitude 8.0 after passing perihelion on August 1 and has since dimmed to 12th magnitude as it retreats from Earth.

Mars Landers

We await anxiously for ET to Phone Home! Our extra terrestrial Martian rover Opportunity was subjected to the planet-wide dust storm on Mars which began in June and is currently dissipating. We lost all communication with the rover as the dust storm blanketed its solar panels with dust and available solar energy dropped catastrophically. Battery charge deteriorated to the point where the rover dropped into deep sleep, and mission scientists are desperately trying to waken it. Once the dust storm settles to the point where the solar panels should start to recharge the batteries, a process which may be aided by solar panel clearing winds, NASA plans to allow 45 days for continuing the reawakening procedures before abandoning efforts. Scientists familiar with the mission question the short time allocated and believe that they are not being given a fair shot to awaken the rover. They suggest that a more reasonable schedule for Opportunity would allow for the same effort that was made to awaken Spirit (March 22, 2010 to May 25, 2011).

Send a postcard to NASA to encourage extending the schedule here:


Curiosity is not subject to the same communication and functional problems as Opportunity because it runs on the onboard Multi-Mission Radioisotope Thermoelectric Generator, or MMRTP, an energy source that relies on the heat generated by decaying plutonium dioxide.

The drilling program at the Duluth site in the Blunts Point Member of the Murray Formation began on May 23rd (Sol 2060-2061), and Curiosity analyzed atmospheric samples for methane on Sol 2075. Then, with the Duluth drilling successfully completed, the rover pulled away from Duluth on Sol 2087 (June 19th) and headed uphill, reaching the crest of Vera Rubin Ridge at the end of the month on Sol 2094. Two attempts to drill into the Pettegrove Point Member of the Murray Formation at Ailsa Craig and Voyageurs failed due to the excessively hard rock making up the crest of Vera Rubin Ridge.

A drilling attempt on target Stoer was successfully completed by Sol 2138 (Aug 13th). Stoer was selected as a target because it exhibited the following features: (1) The DRT brush was able to slightly scratch the surface of the rock, (2) the drilling site is in a slight depression, and (3) the rock surface is evidently softer than the calcium sulfate veins which permeate the rock formation and project above it. Calcium sulfate on Earth makes up two minerals,— gypsum (hardness 2.0) and anhydrite (hardness 3.5). Therefore the rock formation must be softer than 3.5 or possibly 2.0. These characteristics taken together indicated the presence of softer rock, an hypothesis confirmed by the ensuing successful drilling.

Meteor Showers

According to Guy Ottewell’s 2018 Astronomical Calendar, the following meteor showers grace September skies:

  • Sep. 1 SAT.: Aurigids. Active Aug 28-Sep 5. ZHR ~5. 2 days before Last Quarter Moon.
  • . 9 SUN.: September Epsilon Perseids. Active Sep 5-21. ZHR ~10. Near New Moon. Very favorable.
  • . 27 Thu.: Daytime Sextantids. Active Sep 9- Oct 9. ZHR ~5.
  • All three are relatively minor showers. The Epsilon Perseids are the best with an average of 10 meteors per hour in dark moonless skies when light pollution is absent.

    Planet Plotting

    Venus (-4.3 to -4.4) is in Virgo in September and sets less than an hour after the Sun. It is bright enough to be seen in the glow of sunset. The waxing crescent Moon will be 10.0° north of Venus on the 12th at Noon and northeast of Venus that evening. On the 28th Venus will be about 14° WSW of Jupiter. Mercury (-0.8) will be low in the west after sunset in early September after which it will disappear into the glow of the Sun. It then brightens to magnitude -1.6 before reaching Superior Conjunction on the 20th when it is on the other side of the Sun. Mercury may reappear in the east at magnitude -0.8 slightly before sunrise at month’s end.

    Jupiter (-1.8 to -1.7) is in Libra in the western evening sky. The waxing crescent Moon is 4° north of Jupiter on the 13th. Saturn (+0.4 to +0.5) in Sagittarius is low in the southwest after sunset and sets in the latter part of the evening. The waxing gibbous Moon passes within 2° of Saturn on the 17th. After moving from Capricornus to Sagittarius in July, Mars returns to Capricornus in September. It is the bright orange beacon in the southern evening sky and sets after midnight.

    Although it is more than a month since opposition, Mars remains bright at magnitudes -2.1 to -1.3 in Capricornus. Telescopic views sufficient to see surface details improved from those seen at opposition after the planet-wide dust storm settled down.

    Best viewing will be during the first half of the month during the weeks before and after New Moon when Mars is highest in the mid-evening southern sky. A waxing gibbous Moon will be 4° north of Mars in the southern sky on the 20th, after which Mars is best seen in the early evening before Moonrise.

    Neptune (+7.8) in Aquarius and Uranus (+5.7) in Aries rise an hour and 2+ hours after Mars in the afternoon. The waning gibbous Moon passes within 2° of Neptune on the 23rd and 5° Uranus on the 27th.

    PlanetConstellation(s)MagnitudePlanet PassagesTime, Date
    SunLeo/Virgo-26.8New Moon
    Earth, Fall Equinox
    2:01PM EDT, 9/9
    9:54PM EDT, 9/20
    MercuryLeo/Virgo-0.8 to -1.6 to -0.8Superior Conjunction10:00PM EDT, 9/20
    VenusVirgo-4.3 to -4.4Jupiter, 13.8° ENE8:00PM EDT, 9/28
    MarsSagittarius, Capricornus-2.1 to -1.3  
    JupiterLibra-1.8 to -1.7  
    SaturnSagittarius+0.4 to +0.5  

    Autumnal Equinox

    The equinox is at 9:54PM EDT on September 22nd. On the equinox, the axis of the Earth is at right angles to a line between the Earth and Sun and is tilted in the direction of motion of Earth in its orbit. This results in 12 hours of daylight and 12 hours of darkness everywhere on Earth and marks the start of autumn in the northern hemisphere.

    The equinox also coincides with higher frequency of northern lights displays due to intensified flow of charged particles from the Sun. Although not fully understood, this may be due to favorable orientation of Earth's geomagnetic field relative to that of the solar wind magnetic field. The resulting positive interference of geomagnetic and solar wind waves may increase the cascade of ions which excite atoms in the atmosphere above Earth’s magnetic poles, causing them to glow.

    September Moon

    The New Moon of September on the 9th at 2:01PM EDT is the beginning of Lunation 1184 which ends 29.37 days later with the New Moon of October on the 8th at 11:47PM EDT.

    The Full Moon on the 24th at 10:52PM EDT is the first full moon after the equinox and is known as the “Harvest Moon.” Celts called it the “Singing Moon,” and Colonial Americans called it the “Harvest Moon” Chinese refer to it as the “Chrysanthemum Moon,” and it was the “Barley Moon” in Medieval England. Anishinaabe (Odawa and Ojibwe people) recognize it as “Wabaabagaa Giizis" (Leaves Turning Moon.)

    Lunar Perigee (closest to Earth) is 224,533 miles or 56.65 Earth radii on the 7th at 9:20PM EDT. Apogee (maximum orbital distance) occurs on the 19th at 8:53PM EDT when the Moon is at 251,578 miles (63.48 Earth radii).

    PlanetConstellationMagnitudeMoon PassageMoon PhaseMoon Age
    SunLeo-26.85:548AM EDT, 8/112New0 days
    MercuryCancer+4.30.89°NNE, 7:00PM EDT, 9/8Waning Crescent28.54 days
    VenusVirgo-4.210°N, Noon EDT, 9/12Waxing Crescent2.92 days
    MarsCapricornus-2.35.0°N, 3:00AM EDT, 9/20Waxing Gibbous11.54 days
    JupiterLibra-1.94.0°N, 10:00PM EDT, 9/13Waxing Crescent4.33 days
    SaturnSagittarius+0.32.0°N, Noon EDT, 9/17Waxing Gibbous7.92 days
    UranusAries+5.75.0°S, 3:00AM EDT, 9/27Waning Gibbous17.54 days
    NeptuneAquarius+7.82.0°S, Noon EDT, 9/23Waxing Gibbous13.92 days


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