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September 2016 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: Camelopardalis, Perseus, Cassiopeia, Andromeda, Pegasus, Cepheus, Cygnus, Lyra, Aquila, Ophiuchus, Hercules, Draco, Ursa Minor, Ursa Major, Bootes

Comet Journal

The brightest comet in September is Comet C/2013 X1 (PanSTARRS). It is visible in large binoculars and small telescopes at 10th magnitude in southern hemisphere skies south of the tail of Hydra. 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. Autumn skies will lack bright comets unless a heretofore undiscovered one makes an unexpected appearance. However, northern hemisphere observers will get Christmas and Easter comets which may achieve naked eye visibility. The former is Comet 45P/Honda-Mrkos-Pajdusakova and the latter is Comet 41P/Tuttle-Giacobini-Kresak. They will make their respective appearances in November and February in Scorpius and Cancer.

Mars Landers

Opportunity is on the rim of Endeavour Crater exploring a large valley cutting through the rim. The rover neared completion of its investigation within Marathon Valley and was exiting the valley and as it approached the north side of the valley on Sol 4446 (July 26, 2016). It moved into position for an week-long color panorama of the north wall (Gibraltar II) and the geologic contact with the valley floor. On Sol 4453 (Aug. 3, 2016), the rover moved about 19 feet (6 meters) closer to an exposed outcrop after taking more color Panoramic Camera (Pancam) panoramas of Gibraltar II. Then, over the next two sols, Opportunity continued with more Pancam images of Gibraltar II and an outcrop contact from the close vantage point.

On Sol 4456 (Aug. 6, 2016) the rover resumed its exit trip with a 102 feet (31-meter) drive. Mid-drive Pancam imaging was collected which showed interesting ridges or grooves suggestive of fluvial action that the science team decided to go back to examine with both short-baseline and long-baseline multi-spectral stereo image data with the Panoramic Camera (Pancam). On Sol 4459 (Aug. 9, 2016), Opportunity drove about 43 feet (13 meters) to the northwest to set up for the first station of the long-baseline stereo imaging. After several sols of imaging, the rover drive about 16 feet (5 meters) north to set up for the second station of the long-baseline stereo imaging. Over the next few sols, Opportunity collected many more Pancam multi-spectral image frames. The science team is constructing a detailed digital elevation model of the terrain containing the grooves.

Opportunity's explorations during the last year in Marathon Valley yielded the information which first attracted mission scientists to the valley which cuts through the western rim of Endeavor Crater. Satellite observations revealed spectral evidence for the presence of clay minerals which may have developed in the presence of water. Opportunity found residue of ancient iron magnesium clay throughout the brecciated rocks of the Shoemaker Formation which was formed billions of years ago when the impact which excavated Endeavor Crater occurred. There is no evidence for nearby ancient water bodies but the floor of the valley is striped by red bands or troughs composed of red, crumbly material loaded with magnesium sulfate but lacking the iron magnesium clays. The red bands are thought to be associated with fracture zones in the bedrock which permitted the upward movement of water solutions through the Shoemaker Formation, altering the surrounding rock.

From Sol 4445 (June 25, 2016) through Sol 4473 (Aug. 23, 2016) Opportunity traveled 0.30 miles achieving a total distance on Mars of 26.78 miles (43.10 kilometers). Solar array energy production averaged 595 watt-hours per day.

Curiosity is now autonomously choosing targets for laser spectrometer and telescopic examination with the rover's ChemCam instrument. Software recently developed at NASA's JPL laboratory was downloaded and installed in order to supplement the capabilities of the Science Laboratory. Most targets will still be selected by mission scientists, but the new capability will be of particular importance when Curiosity is experiencing delays in communication with Earth.

Similar software has been in use since arrival on Mars to examine wide-angle images for autonomously targeting rocks for higher resolution cameras. The new capability permits collection of data which reveals chemical composition of the targets and also allows for more accurate aiming for fine scale targets. This sounds exactly like the equipment we wished we had as graduate geology students. We envisioned an instrument which we could point at a rock outcrop as we drove by on the highway and determine rock composition, texture, fabric, position, and fossil content. We were going to use the collected data to prepare a tome titled "Super Geology for Simple Minds."

Curiosity spent most of August driving and taking panoramic images. The rover drove into an area of large blocks of Murray Formation bedrock on Sol 1416-1417 (July 29, 2016) which appeared to be good drilling targets. Marimba was drilled on Sol 1420 and the procedure produced an unusually shallow hole due to rock hardness. Sufficient material was obtained for analysis so driving and imaging continued through August so as to reach the next drilling target.

Meteor Showers

Perseid Update: The Perseid Meteor Shower on August 12th more than lived up to its reputation as the best summer meteor shower. Observers in dark skies saw up to 150 - 200 meteors in dark skies, making it the the best Perseid Shower in years. By some definitions, it could even be called a meteor storm.

Unfortunately, September will not be so kind to observers. The minor shower of September is the Epsilon Perseids on the 9th which peaks out at about 5 meteors per hour in dark skies.

Autumnal Equinox

The Equinox is at 10:21AM EDT on the 22nd, 6 days after Full Moon. The noon Sun is directly above Earth's equator, and a line between Earth and the Sun is at right angles to Earth's axis, marking the transition from Summer to Autumn. Each hemisphere receives equal amounts of sunlight causing day and night to be of equal length over the entire Earth on the Equinox.

Planet Plotting

Venus (-3.9) and Jupiter (-1.9 to -1.7) in Virgo are visible in the western sky above the horizon immediately after sunset in September. On the 2nd, a very thin waxing crescent Moon pairs with Jupiter between Venus and the Sun. By midmonth, Jupiter is approaching conjunction with the Sun on the 26th and is lost in its glow.

Saturn and Mars spend most of September in Ophiuchus which is in the southwestern sky in the early evening. September is the time for observers with telescopes to obtain their last great views of the red planet during this apparition. As Earth forges ahead in its orbit, Mars is falling behind and diminishing in brightness after dominating the southern evening sky during its opposition this summer. Both set well before midnight.

Neptune (+7.8) in Aquarius and Uranus (+5.8) in Pisces rise before sunset and set in the wee hours after midnight. Neptune is at its brightest of the year on the 2nd when it is at opposition.

Mercury departs from the evening skies and is the morning planet in Leo in September after its Inferior Conjunction on the 12th. The swiftly moving planet makes its best morning appearance of the year when it reaches Maximum Western Elongation on the 28th at 17.9° from the rising Sun. It will rise over an hour before the Sun.

PlanetConstellationMagnitudePlanet Passages
SunLeo-26.8New Moon, 9/1, 5:03AM EDT
SunVirgo-26.8New Moon, 9/30, 8:11PM EDT
MercuryVirgo, Leo+1.2 to -0.61Inferior Conjunction, 9/12, 8PM EDT
Max. West Elongation, 9/28, 4PM EDT
MarsScorpius, Ophiuchus, Sagittarius-0.3 to +0.1 
JupiterVirgo-1.7Solar Conjunction 9/26, 3AM EDT

September Moon

The New Moon of September on the 1st at 5:03AM EDT will produce an annular eclipse in central Africa. This New Moon is the beginning of Lunation 1159 which ends 29.63 days later with the New Moon of September 30th at 8:11PM EDT.

The Full Moon in September is in Aquarius occurs at 3:05PM EDT on the 16th and produces a penumbral eclipse. It is normally called the "Fruit Moon" but this year is the "Harvest Moon" because it is the full moon closest to the Autumnal Equinox. It was the "Singing Moon" for the Celts, Chinese celebrate the September Moon as the “Chrysanthemum Moon", and to Medieval English, it was the “Barley Moon”.

It was also called the "Harvest Moon" in Colonial America, a reference that traces its origin to European settlers who brought the tradition from the Old World. Farmers utilized the light of the Moon to facilitate the harvest. At this time of year, the path of the setting Moon makes a small angle with the horizon so that its setting takes an inordinately long time, providing light long after sunset. The Moon is at the apogee position in orbit (maximum orbital distance) at 251,689 miles (63.51 Earth radii) from Earth on the 6th at 2:45PM EDT. Perigee distance is 224,872 miles or 56.74 Earth radii on the 18th at 1:00PM EDT.

PlanetConstellationMagnitudeMoon PassageMoon Phase/Age
SunLeo-26.85:03AM EDT, 9/1New ~ 0 days
SunVirgo-26.88:11PM EDT, 9/30New ~ 0 days
MercuryVirgo+1.26.0°N, 1PM EDT, 9/2Waxing Crescent ~ 1.33 days
MercuryLeo-0.60.7°S, 7AM EDT, 9/29Waning Crescent ~ 27.29 days
VenusVirgo-3.91.10°N, 7AM EDT, 9/3Waxing Crescent ~ 2.08 days
MarsOphiuchus-0.18.0°N, 10AM EDT, 9/9Waxing Gibbous ~ 9.25 days
JupiterVirgo-1.70.4°N, 6PM EDT, 9/2Waxing Crescent ~ 1.54 days
SaturnOphiuchus+0.54.0°N, 5PM EDT, 9/8Waxing Crescent ~ 7.50 days
UranusPisces+5.73.0°S, 1PM EDT, 9/18Waning Gibbous ~ 17.33 days
NeptuneAquarius+7.81.2°N, 4PM EDT, 9/15Waxing Gibbous ~ 14.46 days

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