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August 2016 Skies
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by Dick Cookman
Highlights: Comet Journal, Martian Landers, Meteor Showers, Planet Plotting, August Moon
Focus Constellations: Perseus, Cassiopeia, Andromeda, Pegasus, Cepheus, Cygnus, Lyra, Aquila, Ophiuchus, Hercules, Draco, Ursa Minor, Ursa Major, Bootes
July's brightest comet is Comet C/2013 X1 (PanSTARRS). It is visible in larger binoculars at 9th magnitude in southern hemisphere skies south of the tail of Hydra in August. It achieved naked eye visibility in dark skies in June when closest to Earth and was closest to the Sun at perihelion in April. During the last part of 2016 it 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 rover is nearing the completion of its investigation within Marathon Valley and is engaged in one of its final big in-situ campaigns in the valley. As the rover examined the center of the area where the spectral signatures of clay-bearing rocks on the valley floor were detected from orbit, streaks of red-toned, crumbly material were found on the valley’s southern flank. The science team chose to investigate this apparently weathered material. The rover approached exposures of it to prepare for using the Rock Abrasion Tool, called the RAT. This tool grinds away a rock’s surface to expose the interior for inspection.
“What we usually do to investigate material that’s captured our interest is to find a bedrock exposure and use the RAT,” Squyres said. “What we didn’t realize until we took a close-enough look is that this stuff has been so pervasively altered, it’s not bedrock. There’s no solid bedrock you could grind with the RAT.”
Instead, the rover exposed some fresh surfaces for inspection by scuffing some of the reddish material with a wheel.
Squyres said, “In the scuff, we found one of the highest sulfur contents that’s been seen anywhere on Mars. There’s strong evidence that, among other things, these altered zones have a lot of magnesium sulfate. We don’t think these altered zones are where the clay is, but magnesium sulfate is something you would expect to find precipitating from water. "Fractures running through the bedrock form conduits through which water could flow, transport soluble materials, and alter the rock to create the pattern of red zones that we see."
From Sol 4404 (June 14, 2016) through Sol 4445 (July 25, 2016) Opportunity traveled 0.12 miles achieving a total distance on Mars of 26.75 miles (43.05 kilometers). The solar array energy production averaged 635 watt-hours per day, a rather remarkable level for the middle of the Martian winter.
Curiosity began July by putting itself into safe standby mode on the 2nd. Since the most likely cause is thought to be a software mismatch in onboard communication of image data, mission scientist will change modes of communication. Let's hear it for redundant systems. Despite the temporary shut down, NASA approved a two year extension starting on Oct. 1st for the mission which determined in its 1st year that freshwater lakes and rivers on Mars provided environmental conditions suited to microbial life 3 billion years ago at a time when Earth provided similar conditions and hosted abundant microbes. The rover found sulfur, nitrogen, oxygen, phosphorus, and carbon -- the key ingredients necessary for life in its 2012-2013 investigations of the "Sheepbed" mudstone in Yellowknife Bay. The investigations also revealed clay minerals and low levels of salt suggesting deposition from fresh water with moderate oxidation levels which was of neutral acidity or moderately alkaline. The spectrum of oxidized through non-oxidized chemicals provided a chemical energy gradient like that preferred by many organisms on Earth.
The current red color of Mars is due to strongly oxidized iron and other atoms, the gray colors exhibited in many of the drilling samples suggest much lower oxidation levels which would be more conducive to life. Curiosity is investigating older rocks than those examined by Opportunity which appear to have been deposited from saline water with much more acidity creating a very limited chemical energy gradient with little energy availability for lifeforms. The high salinity would have impeded microbial metabolism for any life which could survive in the acidic environment indicating that by the time the rocks investigated by Opportunity were formed, environment conditions favoring life had already deteriorated.
Curiosity reached Mars in August, 2012 and, after its 1st year discoveries, spent 3 years investigating the exact nature of the ancient wet environments in Gale Crater. The next phase of study is focused on the geologic evolution recorded in the progressively younger layers of rock preserved in Mt. Sharp which the rover is currently ascending. Mission scientist hope to determine the nature and cause of the environmental changes which resulted in the transition of a wet Mars to the dry, inhospitable conditions currently exhibited. Such information may provide indications of how a similar transition may be avoided on Earth.
The best meteor shower of the Summer started in mid-July and will continue until late August. The Perseids will peak on the 12th and may be stronger than normal. The Perseid meteors are bits of dust, sand, pebbles, and rocks strewn along the orbit of Comet 109P Swift-Tuttle which last passed through the inner solar system in 1992. The comet's orbit also passes by that of Jupiter. The last time Jupiter was at the location where the two orbits are in closest proximity, its gravity gathered cometary debris in the comet orbit into a clump which has since moved to the location where the comet orbit and that of Earth are in close proximity (the debris shares the same orbit as the comet, so it moves at a similar rate).
On the 12th, Earth will arrive at this location and as we plunge through the clump, an outburst of meteors may fill the night sky. Although normal Perseid rates are about 50 per hour in dark skies, meteor observers and scientists are speculating that rates may approach 150 to 200 per hour. The Perseids are typically bright, fast, and colorful meteors producing long trails with occasional flares at trail's end. The slightly gibbous waxing Moon will rise in the afternoon and will set after midnight leaving a glare free sky in the wee hours before dawn when North America is orbiting headfirst into the river of meteoric debris.
The Kappa Cygnids on the 17th and the Aurigids on the 31st are much weaker showers typically producing about 5 meteors per hour.
The western evening sky in August hosts the planets Mercury (-1.6 to -0.2), Venus (-3.9), and Jupiter (-1.9 to -1.7) in Leo and Virgo. In early August they are lined up with a very bright Venus closest to the horizon yet still very visible in the glare of the setting Sun. Bright Jupiter is highest, with Mercury in between and almost lost in the glow of sunset. Mercury is highest in the sky on the 16th when at maximum eastern elongation (27° from the Sun) but will have to complete with an almost full waxing gibbous Moon. During August, Jupiter will drop closer to the horizon as Venus climbs higher and appears to approach the giant planet. The southern sky has Mars (-1.4 to -0.8) in Libra and Scorpius and Saturn (+0.2 to +0.3) in Ophiuchus while Neptune (+7.8) in Aquarius is rising in the east. The predawn hours display Neptune in the southwest and Uranus (+5.8) in Pisces in the south.
There are three planetary conjunctions at the end of the month when the Moon is in its waning crescent phase. Mars passes within 4° of Saturn at 2PM EDT on the 25th, and, on the 27th two more conjunctions occur. Venus is 5° from Mercury at 1AM EDT and appears very close (0.07°) to Jupiter at 6PM EDT.
|Sun||Cancer, Leo||-26.8||New Moon, 8/2, 4:45PM EDT|
|Mercury||Leo, Virgo||-0.2 to +1.1||Max. East Elongation, 8/16, 5PM EDT|
Venus, 0.5°N, 8/27, 1AM EDT
|Venus||Leo, Virgo||-3.8||Mercury, 0.5°S, 8/27, 1AM EDT|
Jupiter, 0.07°S, 8/27, 6PM EDT
|Mars||Libra, Scorpius||-0.8 to -0.3||Saturn, 4°N, 8/25, 2PM EDT|
|Jupiter||Virgo||-1.7||Venus, 0.07°N, 8/27, 6PM EDT|
|Saturn||Ophiuchus||+0.3 to +0.5||Mars, 4°S, 8/25, 2PM EDT|
The New Moon of August on the 2nd at 4:45PM EDT is the beginning of Lunation 1158 which ends 29.51 days later with the New Moon of September 1st at 5:03AM EDT.
The Full Moon in August is in Aquarius and occurs at 5:27A M EDT on the 18th. It is known as the "Grain or Green Corn Moon" and was the "Dispute Moon" for the Celts. Chinese celebrate the August Moon as the “Harvest Moon" and to Medieval English it was the “Corn Moon”.
It was called the "Dog Day's Moon" in Colonial America, a reference that traces its origin to the ancient Egyptians who designated the time following the helical rising of Sirius (the "dog star" in Canis Major) as the "dog days". The helical rising of Sirius occurred when Sirius rose just before the Sun and was a calendar marker for the Egyptians because flooding of the Nile was soon to follow. Sediment deposited by the flood renewed the soil, allowing the continuous cropping of the same region necessary for survival of their civilization. The helical rising permitted the development of the first accurate annual calendar which replaced earlier lunar calendars based on months.
The Moon is at the apogee position in orbit (maximum orbital distance) at 251,197 miles (63.38 Earth radii) from Earth on the 9th at 8:05PM EDT. Perigee distance is 228,074 miles or 57.55 Earth radii on the 21st at 9:19PM EDT.
|Planet||Constellation||Magnitude||Moon Passage||Moon Phase/Age|
|Sun||Cancer||-26.8||4:45PM EDT, 8/2||New ~ 0 days|
|Mercury||Leo||-0.2||0.6°S, 6PM EDT, 8/4||Waxing Crescent ~ 2.05 days|
|Venus||Leo||-3.8||3.0°S, 2AM EDT, 8/4||Waxing Crescent ~ 1.39 days|
|Mars||Scorpius||-0.6||8.0°N, 6PM EDT, 8/11||Waxing Gibbous ~ 9.05 days|
|Jupiter||Virgo||-1.7||0.2°S, Midnight EDT, 8/5||Waxing Crescent ~ 2.30 days|
|Saturn||Ophiuchus||+0.4||4.0°N, 8AM EDT, 8/12||Waxing Gibbous ~ 9.64 days|
|Uranus||Pisces||+5.8||3.0°S, 6AM EDT, 8/22||Waning Gibbous ~ 19.55 days|
|Neptune||Aquarius||+7.8||1.1°N, 8AM EDT, 8/19||Waning Gibbous ~ 16.64 days|