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June Skies (2007)

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June Skies - by Dick Cookman

Highlights: Comet Journal, Martian Landers, Planet Plotting & Summer Solstice, Meteors, Hothouse Mars?, June Moon
Focus Constellations: Coma Berenices, Virgo, Bootes, Hercules, Lyra, Draco, Ursa Major

Comet Journal

Comets 2P/Enke, C/2006 P1 McNaught, 96P Macholtz 1 and C/2007 E2 have all faded to magnitude 11.0 or dimmer after peaking in January through April when passing the Earth and Sun. All are retreating from the inner solar system, leaving comet observers with a dearth of bright (or dim) comets for June.

Martian Landers

After Opportunity returned to the edge of Tierra del Fuego to continue long distance stereo imaging of Cape St. Vincent to find likely paths for entry into Victoria Crater, the rover proceeded northward on Sol 1157 (April 26th) to a collection of rocks (Granada) to test its D-Star hazard avoidance software then backtracked counterclockwise around the crater toward the Cape of Good Hope to view Cape St. Vincent from the opposite side.
The lower layer of rock in the crater wall at Cape St. Vincent exhibits prominent cross-bedding indicative of air or water current deposition of the sediment from which the rock layer originated. On May 9th (Sol 1170), Opportunity arrived on the at the rim of the Cape of Good Hope above Madrid/Guadarrama, an outcrop exposed in the wall of the crater. Cobbles strewn around on the ground in the vicinity of Victoria Crater appear to be ejecta composed of the same materials as Madrid/Guadarrama and contain many "blueberries." Blueberries are small rounded rocks which may have been subjected to abrasion by sand and pebble bearing currents during initial formation of the rock layers.

The rover was able to face its solar panels into the wind numerous times during April and May which helped clean dust and debris which has accumulated during its time on Mars. As a result, the electrical output of the solar cells has returned to levels not experienced since it initially arrived on the planet, 1177 Martian days and 10,791 meters (6.71 miles) ago.

On Sol 1164 (April 12, 2007). Spirit arrived at a pockmarked outcrop, Madeline English, near the edge of the Home Plate plateau after conducting studies of Elizabeth Mahon, a rock outcrop containing light colored silica rich clasts or fragments. These clasts have the highest levels of silica yet observed on Mars which indicates formation processes associated with liquid water. In contrast, Madeline English contains clasts which appear to have a different origin than the surrounding material. This would support the hypothesis that this outcrop reveals one of the region's lowest (and oldest) rock layers.

From Sol 1171 (April 19, 2007) to Sol 1198 (May 17, 2007) the rover examined a variety of light and dark soil targets in and around the rover’s tracks between Home Plate and Mitcheltree Ridge. Although some of the light colored soils, Everett and Slide, are low in silica and rich in iron and magnesium, which is often associated with volcanic rocks, many of the light soils appear to be similar to Elizabeth Mahon and were derived by the breakdown of sedimentary rocks.

By Sol 1198 (May 17, 2007), Spirit had traversed 7,109.47 meters (4.42 miles) on Mars.

Planet Plotting & Summer Solstice

The evening planets put on a rather phenomenal show in June as Mercury (0.5) in Cancer, Venus (-4.3) in Gemini and Cancer, and Saturn (0.5) in Leo cavort in the western sky after sunset while Jupiter (-2.6) in Ophiuchus lights up the southeastern evening sky. At 2:06 PM EDT on the 21st Earth celebrates its Summer Solstice and longest night of 2007.

In early June, Venus can be viewed high in the western sky at dusk in line with and to the south of Castor and Pollux in Gemini. As the sky grows dark, Mercury appears 10 - 15° below Castor and makes a large triangle with Venus and 1st magnitude Procyon in Canis Minor to the south. Saturn is between brilliant Venus and 1st magnitude Regulus in Leo in line with Mercury and Venus. 1st magnitude Capella is north of Venus and Mercury in Auriga and joins in to provide the evening western sky with 7 first magnitude objects after sunset!

During early June, Mercury moves closer to Venus but gets dimmer as our sister planet rises higher in the evening sky. After the 10th, Venus continues to ascend and dims slightly as it approaches its June 30th meeting with Saturn when the two will be less than 1° apart and will provide spectacular views in binoculars or low power telescope eyepieces. Mercury falls back into the glare of sunset after June 10th and disappears from view by month's end.

Mars (0.8) is in Pisces. It rises in the wee hours and is a relatively bright addition to the eastern sky to the west of Mira in Cetus before dawn. Other morning planets include Uranus (5.9) in eastern Aquarius and Neptune (8.0) in eastern Capricornus. Viewing each of these other planets requires binoculars or small telescopes.

June Meteor Showers are typically rather subdued. Early June features the Aretids and the Zeta Perseids which are best known as radio wave showers. The Lyrids of June 16 and the Bootids of June 27 typically have hourly frequencies in the single digits and each will suffer from the glare of the gibbous Moon. The 50 to 100 meteors visible per hour provided by the Bootids in 1998 and 2004 will probably not be repeated in 2007.

Hothouse Mars?

The 2001 NASA report focused on the Southern Polar Cap region of Mars and noted that the Martian Global Surveyor photographed evidence for a significant summertime shrinkage of the polar cap from 1999 to 2001 (1 Martian year), a shrinkage trend that continued for at least 3 Martian years. Like the climate of Earth, that of Mars results from a complex interaction of orbital and planetary position variations, and changes in airborne particulate matter, wind patterns, solar radiation, atmospheric composition, topography and surface composition. These result in a climate that varies both geographically and temporally, tremendously complicating the process of making accurate predictions.

Specific problems of the scenario alluded to above include the following:

— Orbital elements for Mars vary much more than those of Earth causing more drastic changes due to changing solar distance and planetary inclination.
— In the absence of oceans and a thick atmosphere, Mars has much less thermal inertia than does Earth and is more susceptible to changes in any of the climatic factors.
— Dust storms play a much more active role on Mars than on Earth and cause global temperature changes of several degrees on an annual basis.
— From 1999 through 2005 solar output as measured by satellite decreased every year as the 9-11 year sunspot cycle moved toward minimum.

The more likely alternative to a conclusion of global warming for Mars from 1999 to 2005 would be a warming restricted to the south polar region due to localized phenomena such as topography and decreases in atmospheric particulate matter.

As stated on www.realclimate.org, it is interesting that the same folks who attribute Martian glacial melting to global warming reject the much more significant melting on Earth as an indicator of the same.
June Moon

The June Full Moon is on the 30th. The western hemisphere had a Blue Moon in May and the eastern hemisphere takes its turn in June. The June Moon was known as the Rose Moon by Colonial Americans, the Lotus Moon by the Chinese, and the Flower Moon by the English. Anishnaabe (Chippewa and Ojibwe) call it "Ode’imini-giizis" (Strawberry Moon).

Jupiter is 6° north of the waning Moon at 8:00 AM EST on June 1st, two hours after setting and a day after May's Blue Moon. At 6 PM EST on June 10th, Mars is 5° south of a waning crescent Moon and can be seen southeast of the Moon after sunset. Venus is within one degree of a 4 day old waxing crescent Moon at 11 AM EDT on the 18th and can be viewed within 6° after sunset. Saturn is just as close at 4 AM EDT on the next morning and can be seen within 3° of the Moon before setting at midnight. On the 28th, Jupiter repeats its June 1st proximity to the waxing gibbous Moon at 10 AM EDT.


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