May Skies

by Dick Cookman

05/6/2016

Highlights: Comet Journal, Martian Landers, Meteor Showers, Grand Traverse Astronomical Society, Planet Plotting, May Moon

Focus Constellations: Lynx, Ursa Major, Draco, Ursa Minor, Cepheus, Cassiopeia, Camelopardalis, Perseus, Auriga, Gemini, Cancer, Leo, Coma Berenices, Virgo, Bootes, Hercules, Lyra

Comet Journal

Comet 252P/LINEAR (2016) is between Ophiuchus and Serpens Caput at magnitude 6.5 after passing through perihelion in March. It will circle through Ophiuchus during the Spring and early Summer as it moves outward toward and beyond Jupiter's orbit.

Comet C/2013 X1 (PanSTARRS) is about 8th magnitude in Aquarius. It passes through perihelion on April 20th and may reach 6th magnitude in June when passing within 56 million miles of Earth between the orbits of Earth and Mars. It will appear south of Capricornus in morning skies.

Mars Landers

Opportunity is up on the steep slopes of "Knudsen Ridge" in Marathon Valley on the rim of Endeavour Crater. It is currently engaged in seeking out specific rock outcrops to find evidence for clay minerals. At each drive location, the rover collects a 360-degree Navigation Camera (Navcam) panorama plus targeted multi-filter (color) Panoramic Camera (Pancam) panoramas.

On Sol 4334 (Apr. 2, 2016), the rover headed westward for 15.4 meters then turned southwest on the 5th (Sol 4337). A target was identified and on Sol 4345 (Apr. 14, 2016) the rover moved 2.5 meters to reach "Pierre Pinaut" and performed an Alpha Particle X-ray Spectrometer (APXS) measurement and extensive Navigation Camera (Navcam) panoramas and targeted multi-filter (color) Panoramic Camera (Pancam) panoramas. On Sol 4357 (Apr. 26, 2016) the Rock Abrasion Tool on the robotic arm was used to prepare the rock surface for more APXS measurements.

From Sol 4334 to Sol 4357, the solar array energy production has ranged between 617 and 650 watt-hours/day providing sufficient energy for full operations. The total distance that Opportunity has traveled on Mars in the last 12 years is 26.58 miles (42.78 kilometers).

On March 10th, Curiosity attempted to climb the steepest slope attempted by any Mars rover when climbing onto the top of the Stimson Formation. The rover surmounted a slope of 32° before slippage prevented it from reaching the clay mineral target a few inches farther upslope. Mission scientists reluctantly eliminated the target when they chose an alternative route to the top. Curiosity then proceeded to cross the rugged sandstone terrain of the 1/4 mile wide Naukluft Plateau which is carved into ridges and knobs by millions of years of wind erosion. The sandstone itself appears to have been formed as windblown sand dunes lithified into rock.

As the rover continues its journey toward the top of Mt. Sharp, it will soon reach an area of lake-bed mudstone. Beyond that are 3 geologic units. The first exhibited the spectral signature of hematite (Fe2O3) in satellite images, the second revealed clay minerals spectra and the third which is 4.7 miles away showed sulfate spectra.

Meteor Showers

Waning crescent Moon skies provide almost ideal conditions for the Eta Aquarid meteor shower on the 5th when Earth plunges through the river of debris scattered in space from previous passages of Comet Halley. Aquarius rises in the east during the hours before dawn and cloudless skies unpolluted by glare from insecurity lights maximize the number of visible meteors. Meteor counts ranged from 10 to 150 per hour in previous years, but will probably be closer to the former this year. But hope springs eternal! The Eta Lyrid shower on the 8th is a minor shower without much punch.

Grand Traverse Astronomical Society

Northwestern Michigan is blessed with relatively dark night skies and limited light pollution in the countryside between towns. In addition to the Headlands International Dark Sky Park near Mackinaw City with their comprehensive year-round programs, it is also the location of the Sleeping Bear Dunes National Lakeshore Park where light pollution is almost non-existent. As a result, there are numerous astronomical societies, clubs and supporting organizations in the area, one of which is the Grand Traverse Astronomical Society (www.gtastro.org). GTAS promotes public viewing sessions in conjunction with Northwestern Michigan College which has an observatory south of Traverse City. The Society also partners with the Sleeping Bear Dunes National Lakeshore (SBDNL) and holds viewing sessions at locations within the park at the Visitor's Center, the Dune Climb, and at Platte River Point in Benzie County. Other observation sessions include their visits to sites on the bay, at the library, and downtown in Traverse City, in Antrim County and Acme, at Leelanau State Park, and in Leland. Their excellent website has a schedule for 2016 which shows that they host almost forty public celestial viewing sessions and three public solar viewing events during the interval between April 16th and December 2nd. In addition their monthly meetings often include excellent presentations about pertinent astronomical topics.

At each public event, there are numerous telescopes available in addition to the equipment available when meeting at the observatory. The equipment includes a number of SCT telescopes, a solar telescope, a large dobsonian telescope, constellation binoculars, giant binoculars, and a large variety of telescope eyepieces. Observation and telescope experts from the Society volunteer their time and astronomical expertise to make each session an extremely worthwhile event.

Planet Plotting

The morning planets of May include brilliant Venus (-3.8 to -3.9) in Pisces, Aries, and Taurus, Uranus (+5.9) in Pisces, and Neptune (+7.9) in Aquarius. Venus and Uranus are very close to the Sun, rising slightly before the day star makes its appearance. Venus rises less than 30 minutes before sunrise on May 1st and almost with the Sun on the 30th as it approaches solar conjunction on June 6th.

Mars (-1.5 to -2.1) moves from Ophiuchus through Scorpius and into Libra in May and reaches opposition with the Sun on the 22nd. It has been over 2 years since the last opposition, an agonizing wait for Mars observers who are now faced with a target immersed in the glare of a nearby almost full waning gibbous Moon and just 20 to 30° above the southern horizon. Despite the challenging viewing conditions during this opposition, Mars will be closer and brighter than any opposition since 2005 and, at midnight on 5/22, will exhibit its northern polar cap, the Amazonis region with the largest volcano in the Solar System —— Nix Olympus, and the Elysium region where Curiosity is exploring. Mars will be as bright as Jupiter (-2.1) in Leo and will far outshine nearby Saturn (+0.2) in Ophiuchus and the red supergiant Antares(+1.0) in Scorpius. For observers who are not satiated by the events of the 22nd, Mars will be closest to Earth on May 30th when it will shine brightly in the south providing a glareless evening apparition as the waning crescent Moon doesn't rise until midnight. This may actually be a better time for observation. The absence of lunar glare will permit observers to see far more detail on the planet and allow use of eyepieces with higher power in larger telescopes.

In my view, the only planetary viewing that exceeds the quality of observing Saturn is that of Mars near opposition. The Mars opposition of 1956 was so spectacular that it initiated my career of teaching astronomy and of lifelong observation.

Mercury (+3.0 to +0.9) is hidden in the glare of the Sun all month but can be seen between 7:12AM and 2:42PM EDT on the 9th when it transits the Sun during inferior conjunction. Transit frequency averages about 13 per century with significant deviations from the average due to the highly elliptical orbit of Mercury. The last transit was in 2006 and the next will be in 2019. Jupiter (-2.3 to -2.1) in Leo dominates the southeastern evening sky, surpassed only by the Moon.

May Moon

The New Moon of May 6th at 3:30PM EDT marks the beginning of Lunation 1155 which ends 29.34 days later with the New Moon on June 4th at 11:00PM EDT.

The Full Moon of May is in Libra and occurs at 5:14PM EDT on the 21st. It was referred to as the "Milk Moon" in Colonial America. Celts referred to it as “Bright Moon” and Chinese call it “Dragon Moon." To Medieval English it was the “Hare Moon” and Anishinaabe (Chippewa and Ojibwe) of northern Michigan celebrate it as “Zaagibagaa-giizis” (Budding Moon).

There is no "Blue Moon" this month for advocates of the 2 Full Moons per month = a Blue Moon. However for those who prefer 4 Full Moons per season (3 months) = a Blue Moon, this one is the 3rd of 4 so your Moon is blue. Enjoy it!

Perigee distance is 222,344 miles or 56.10 Earth radii on the 6th at 12:13AM EDT. This is the third closest perigee of 2016 and almost coincides with New Moon, causing ocean tides to be higher than normal. The Moon is at the apogee position in orbit (maximum orbital distance) at 252.235 miles (63.64 Earth radii) from Earth on the 18th at 6:06PM EDT.