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July 2016 Skies
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by Dick Cookman
Highlights: Comet Journal, Martian Landers, Meteor Showers, Planet Plotting, July Moon
Focus Constellations: Camelopardalis, Cassiopeia, Cepheus, Draco, Ursa Minor, Ursa Major, Bootes, Hercules, Lyra, Cygnus, Aquila, Ophiuchus, Libra, Virgo, Coma Berenices
The brightest comet in July is Comet C/2013 X1 (PanSTARRS) which, at 6th magnitude, is on the edge of naked eye visibility in very dark skies. It is in southern hemisphere skies throughout July between Scorpius and Centaurus and will be too far south for observers in the northern United States. It passed within 56 million miles of Earth between the orbits of Earth and Mars on June 21st and will rapidly decrease in magnitude as it retreats to the outer Solar System well beyond the orbit of Pluto.
Opportunity is on the rim of Endeavour Crater exploring a large valley cutting through the rim. The Mars Reconnaissance Orbiter (MRO) recorded spectral signatures for clay minerals in the valley, making it an exploration goal because clay minerals are one of the targets in the search for ancient life. The valley was named Marathon Valley because the rover completed a 26 mile marathon on Mars in order to reach it. Between Sol 4379 (May 18, 2016) and Sol 4404 (June 13, 2016), Opportunity examined an unusual area with crumbly red material and yellow pebbles on the valley floor. The rover spun a wheel in order to scuff up the surface so as to proceed with Panoramic Camera (Pancam) 13-filter imaging, Alpha Particle X-ray Spectrometer (APXS) examination, and collection of Microscopic Imager (MI) mosaics of the surface targets. The results of these observations surprised mission scientists. They revealed the highest sulfur contents yet found on Mars. The magnesium sulfate which is the source of these readings is a substance typically precipitated from mineral bearing waters which flow through fractures, alter their margins and change the rock substrate. With studies of these altered zones completed, on Sol 4405 (June 14, 2016) mission scientists directed the rover to move toward the center of the area where clay mineral spectral signatures were observed from orbit. Further investigation continued until Sol 4417 (June 27, 2016) after which the rover prepared to leave the valley and travel to the southeast. During the interval, the solar array energy production ranged between 636 and 658 watt-hours/day, allowing full operations. Total distance traveled by Opportunity on Mars is 26.63 miles (42.85 kilometers).
After landing on Mars in Gale Crater in 2012, Curiosity crossed the crater floor as it headed to Mt. Sharp, the mountain in the middle of Gale Crater which is the erosional remnant of the sedimentary rock layers which once filled the crater. When it reached the base of the mountain in 2014, Curiosity climbed over Murray Formation, the basal layer of Mt. Sharp, and ascended onto the Stimson unit which forms the Naukluft Plateau. It headed westward, crossing the rough 1/4 mile wide terrain of fractured sandstone. The sandstone is composed of ancient sand dunes which formed on top of the partially eroded lower layers of the mountain, were lithified, and finally carved into ridges and knobs by millions of years of wind erosion.
Curiosity has analyzed 12 drilled samples so far on Mars. Many were taken from the floor of the crater and revealed large areas of ancient lake deposits which may have offered conditions favorable for microbes. A recent examination of Number 7, a drill sample collected a year ago in the lake bottom mudstone at Buckskin, revealed the presence of the mineral tridymite which is associated with high temperature silica rich volcanism on Earth. This was unexpected and will probably change current concepts about the volcanic history of Mars because volcanic rocks examined so far on Mars have low silica levels similar to the relatively quiet "hotspot" vulcanism associated with deep seated sources in the mantle. Silica rich lava is associated with explosive volcanic mountain ranges on Earth where tectonic plates collide.
Manganese oxides were recently found in drillings made in 2014 into mineral filled cracks in the Kimberly sandstones. Their presence astonished scientists as it indicates that previously theorized oxygen levels in the ancient Martian atmosphere were too conservative. The red color of Mars results from abundant iron oxide, indicating the presence of free oxygen in the ancient atmosphere. But manganese oxides require oxygen rich conditions to form, they will not form in limited oxygen environments without the participation of microbial life. The Martian atmosphere must have had abundant oxygen and/or widespread microbes. On Earth, manganese oxides were absent until atmospheric levels of oxygen rose to significant levels. Their appearance marked a major transformation in Earth evolution when biologically generated atmospheric oxygen approached levels comparable to today.
Analysis of the sand ripples in Bagnold Dunes creates another situation demanding new explanations. On Earth, wind generated ripples tend to be of two different wavelengths and amplitudes. The size of water generated ripples differs from those of wind. Long wavelength, tall wind ripples form dunes and short wavelength, low ripples form on the windward slope of dunes. Ripples created by moving water tend to fall between the two sizes of wind ripples in wavelength and height. Sediments on Mars also display three different heights and wavelengths of ripples but all are thought to be formed by wind. The intermediate size is similar to water ripples on Earth but must form via a different mechanism since there is no widespread flowing water on Mars. The nature of this mechanism is now a trending topic amongst the sedimentologists who study Mars.
Numbers 10 and 11 came from the fractured sandstone of the Stimson on the plateau and #12 was from the mudstone of the Murray Formation, west of the plateau. The Stimson drillings were positioned to compare the silica and sulfate levels within and away from the pale zones surrounding the fractures in order to determine the nature of the material precipitated from mineral bearing water that flowed through the fractures after the rocks layers were formed.
Current plans are to turn southward and approach the higher parts of the mountain head-on. More elevated regions on the mountainside display seasonal changes of dark streaks in the valleys which may result from flow of surface or near surface waters.
The Piscis Austrinid, Delta Aquarid, and Alpha Capricornid Meteor showers on July 28th and 30th are minor showers which occur in dark skies with little competition from the waning crescent Moon. Unfortunately they are restricted to the southern horizon and are best seen in southern hemisphere skies. Each typically peaks at only 5 to 20 meteors per hour but due to the close timing of the peaks, they may combine to produce a decent shower if the the weather behaves.
July's evening planets include Mercury (-1.6 to -0.2) and Venus (-3.9) in Taurus and Gemini, and Jupiter (-1.9 to -1.7) in Leo. Mercury is at superior conjunction on the 6th and will not be visible until later in the month. Venus just appeared in the evening skies after passing through its superior conjunction in June. Both Mercury and Venus set soon after sunset, leaving Jupiter to reign supreme in the west as Mars and Saturn dominate the southern and southeastern skies.
Mars (-1.4 to -0.8) in Libra is dimmer than it was at at opposition in May but is still almost as bright as Jupiter and outshines Saturn (+0.2 to +0.3) in Ophiuchus which, in turn, is brighter than nearby red supergiant Antares(+1.0) in Scorpius. Mars, Saturn, and Antares near the southeastern horizon after sunset form a conspicuous triangle which moves into southern skies in the mid to late evening after Jupiter sets in the west. The triangle is best seen in early and late July as it has to compete with the nearby gibbous and full Moon in the middle of the month.
Uranus (+5.8) in Pisces, and Neptune (+7.8) in Aquarius are dim morning planets in early and mid-July and lost in the glare of the Moon at the end of the month.
|Sun||Gemini, Cancer||-26.8||New Moon, 7/4, 7:01AM EDT|
|Mercury||Taurus, Gemini, Leo||-1.6 to -0.2||Superior Conjunction, 7/6, 11PM EDT|
Venus, 0.5°S, 7/16, 2PM EDT
|Venus||Taurus, Gemini||-3.9||Mercury, 0.5°N, 7/16, 2PM EDT|
|Mars||Libra||-1.4 to -0.8|
|Jupiter||Leo||-1.9 to -1.7|
|Saturn||Ophiuchus||+0.2 to +0.3|
The July New Moon on the 4th at 7:01AM EDT is the beginning of Lunation 1157 which ends 29.41 days later with the New Moon of August 2nd at 4:45PM EDT.
The Full Moon of July is in Sagittarius and occurs at 6:57PM EDT on the 19th. It is known as the Flower Moon, Rose Moon, Strawberry Moon, or Honey Moon and was referred to as the "Summer Moon" in Colonial America. Celts referred to it as “Moon of Claiming” and Chinese call it “Hungry Ghost Moon." To Medieval English it was the “Mead Moon” and Anishinaabe (Odawa and Ojibwe) of northern Michigan celebrate it as "Abitaa-niibini-giizis" (Halfway Summer Moon).
Perigee distance is 227,411 miles or 57.38 Earth radii on the 1st at 2:40AM EDT. The Moon is at the apogee position in orbit (maximum orbital distance) at 251,201 miles (63.390 Earth radii) from Earth on the 13th at 1:24AM EDT. The Moon is again at perigee on the 27th at 7:37AM EDT at a distance of 229,698 miles or 57.96 Earth radii.
|Planet||Constellation||Magnitude||Moon Passage||Moon Phase/Age|
|Sun||Gemini||-26.8||7:01PM EDT, 7/4||New ~ 0 days|
|Mercury||Gemini||-1.6||5.6°S, 1AM EDT, 7/4||Waning Crescent ~ 29.083 days|
|Venus||Gemini||-3.9||5.1°S, 10PM EDT, 7/4||Waxing Crescent ~ 0.12 days|
|Mars||Libra||-1.1||8.0°N, 2PM EDT, 7/14||Waxing Gibbous ~ 10.29 days|
|Jupiter||Leo||-1.9||0.9°S, 6AM EDT, 7/9||Waxing Crescent ~ 4.96 days|
|Saturn||Ophiuchus||+0.2||3.0°N, 1AM EDT, 7/16||Waxing Gibbous ~ 11.75 days|
|Uranus||Pisces||+5.8||3.0°S, Midnight EDT, 7/25||Waning Gibbous ~ 20.71 days|
|Neptune||Aquarius||+7.8||1.1°N, 2AM EDT, 7/23||Waning Gibbous ~ 18.79 days|