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July 2017 Skies

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July Skies

by Dick Cookman


Highlights: Comet Journal, Martian Landers, Meteor Showers, Planet Plotting, July Moon

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

Comet Journal

41P/Tuttle-Giacobini-Kresak is in eastern Serpens Cauda. After reaching 6th magnitude near perihelion in April, the comet has dimmed to 13th magnitude and is rapidly retreating from the inner solar system. C2015 ER61 (PanSTARRS) is in Aries after passing through perihelion at 6th magnitude in May. It is at 8th magnitude and will move into Taurus in August. Comet V2 Johnson is at 7th magnitude in Virgo in early July. After the middle of the month, it will pass into Hydra then disappear from northern hemisphere skies.

Mars Landers

Opportunity is at "Perseverance Valley” on the western rim of "Endeavor Crater", the 14 mile wide crater located on "Meridiani Planum", the plain where the rover landed in January of 2004. Between Sol 4739 (May 23, 2017) and Sol 4773 (June 27, 2017), Opportunity maneuvered around the top of the spillway to obtain wide-baseline stereo down-valley images for a detailed map revealing the valley topography. This map is for planning a route down the valley to the floor of the crater. On Sol 4750 (June 4, 2017), the left front wheel actuator stalled with the wheel splayed out at a 33 degree angle. After attempting a variety of fixes over the next two weeks, the team started alternating small toe out actuations with attempts to straighten the wheel. The final attempt was successful, but the initial cause of the problem is yet to be discovered. Mission scientist plan to restrict steering to the rear wheels as the right front wheel has been unsteerable for many months and the left front wheel condition is now suspect. Solar array energy production averaged 351 watt-hours per sol during the month and the rover has traveled 27.90 miles (44.90 kilometers) on Mars since 2004.

On Sol 1680 (April 29, 2017), the Curiosity Science Laboratory rover climbed southeastward up Mt. Sharp following tilted Murray Formation layers (some with cross-bedding) toward Vera Rubin Ridge (initially called Hematite Ridge due to spectral hematite signatures obtained from orbit). The layers appear as discontinuous outcrops separated by rocky and sandy surfaces, some with megaripples that are darker and larger than those at Bagnold Dunes. The rover collected sand samples to be examined later and is making MAHLI, APXS, and Chemcam "touch and go" observations of adjacent rock outcrops. One mudstone outcrop slab exhibited color variations (gray, pink and orange) and patchy white veins, others display much darker veins. By Sol 1741 (June 29, 2017), Curiosity was drawing close to the base of Vera Rubin Ridge which is composed of the next youngest layer above the Murray Formation mudstones. Evidence gathered to date from the passage over the floor of Gale Crater and the ascent through the layers of the Murray Formation, the basal layer of Mt. Sharp, indicates that after the formation of the impact crater in the basaltic crust of the planet about 3.5 billion years ago, a lake filled part or all of the crater and sediments later transformed into the rock layers of the Murray Formation accumulated on the lake bottom over 100's of millions of years. The depths of the stratified lake were oxygen poor and the surface waters were oxygen rich. The next pages of Gale Crater’s history will emerge as the rover examines the Vera Rubin Ridge and the layers of Mt. Sharp which lay above.

Meteor Showers

The Southern Delta Aquarid Meteor Shower on the 30th coincides with the 1st quarter Moon which sets slightly after midnight. Minimal lunar glare in the hours before dawn will maximize the shower which averages 15 to 20 meteors per hour in dark skies unpolluted by artificial lights. The meteors originated from the breakup of what are now the Marsden and Kracht Sungrazing comets.

Other meteor showers in July are restricted to the southern hemisphere with the exception of the early stages of the Perseid Shower which peaks on August 12th. The peak will compete with the glare of the almost full moon.

Planet Plotting

Morning planets include Venus (-4.2 to -4.0) in Taurus and Gemini. Uranus (+5.8) is in Pisces, and Neptune (+7.8) is in Aquarius.

Brilliant Venus rises about 3:00AM EDT and is 20° above the horizon by sunup. It is near the waning crescent Moon on the 20th. Uranus and Neptune rise about midnight and are in the southern sky before dawn. The Moon is adjacent to Neptune on the 13th and Uranus on the 16th.

Evening planets in July include Mercury (-1.2 to +0.4) in Gemini, Cancer, and Leo. It is near the waxing crescent Moon on the 25th and is at Maximum Eastern Elongation on the 30th, when it is 27.2° from the Sun and sets in the northwestern sky after sunset. Jupiter (-2.0 to -1.9) in Virgo is in the southwest after sunset and sets about midnight. Saturn (+0.2 to +0.4) is in Ophiuchus in July. Adjacent to the Moon on the 7th, it will dim toward month’s end. Mars (+1.7) in Gemini and Cancer reaches solar conjunction on the 26th and is not observable in July. It is near the waxing crescent Moon on the 23rd, about 2 hours after New Moon.

PlanetConstellation(s)MagnitudePlanet Passages Time Date
SunGemini, Cancer-26.8New Moon 5:46AM EDT 7/23
MercuryGemini, Cancer, Leo-1.2 to 0.4Max. Elong E. 27.2° 1:00AM EDT 7/30
VenusTaurus, Gemini-4.2 to -4.0 
MarsGemini, Cancer+1.7Solar Conjunction 9PM EDT 7/26
JupiterVirgo-2.0 to -1.9 
SaturnOphiuchus+0.2 to +0.4 

July Moon

The New Moon of July 23rd at 5:46AM EDT is the beginning of Lunation 1170 which ends 28.63 days later with the New Moon of August 21st at 2:30PM EDT. The Full Moon of July in Sagittarius occurs at 12:07AM EDT on the 9th. The July Moon is called the “Thunder or Hay Moon”. Colonial Americans called it the “Summer Moon”. To the Celts it was the “Moon of Claiming”, and Chinese refer to it as “Hungry Ghost Moon”. It was the “Mead Moon” in Medieval England. Anishinaabe (Odawa and Ojibwe) people in northern Michigan recognize it as “Aabita-niibino-giizis" (Raspberry Moon).

Lunar Apogee position in orbit (maximum orbital distance) is at 252,236 miles (63.65 Earth radii) from Earth on the 6th at Midnight EDT. Perigee (closest to Earth) is 222,425 miles or 56.64 Earth radii on the 21st at 1:13PM EDT. The proximity of perigee and New Moon will produce higher than normal spring tides.

PlanetConstellationMagnitudeMoon PassageMoon PhaseMoon Age
SunCancer-26.85:46AM EDT 7/23New0 days
MercuryLeo+0.20.84°N, 5:00AM EDT, 7/25Waxing Crescent1.97 days
VenusTaurus-4.12.7°S, 8:00AM EDT, 7/20Waning Crescent25.73 days
MarsCancer+1.73.1°S, 8:00AM EDT, 7/23Waxing Crescent0.09 days
JupiterVirgo-2.02.6°NNE, 5:00AM EDT, 7/1Waxing Gibbous6.60 days
JupiterVirgo-1.93.0°NNE, 6:00PM EDT, 7/28Waxing Crescent5.51 days
SaturnOphiuchus+0.23.2°N, Midnight EDT, 7/7Waxing Gibbous12.39 days
UranusPisces+5.84.1°SSE, 10PM EDT, 7/16Waning Crescent22.31 days
NeptuneAquarius+7.80.83°SSE, 2PM EDT, 7/13Waning Gibbous18.98 days

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