September Skies (2006) – by Dick Cookman
Highlights: Comet Journal, Martian Landers, Planet Plotting, Meteors, Solar Minimum,
Terrestrial Planets, September Moon
Focus Constellations: Lyra, Cygnus, Pegasus, Cassiopeia, Cepheus, Ursa Minor,
Comet 4P/Faye is expected to brighten to 9th or 10th magnitude and may be seen
with binoculars in eastern Pisces and western Aries in September. Through the
month it will move toward the head of Cetus.
Comet 177P/2006 M3 (Barnard 2) is another binocular object (8.8) in Draco which
will be best observed in early September.
C/2006 M4 ( SWAN ) (9.1) is a newly discovered comet which will be north of eastern
Leo in the predawn northern skies in late September. It may increase to 7th magnitude
Opportunity spent the last week of July and the first few days of August adjacent
to Beagle Crater conducting a panoramic survey of the crater. It examined a rock
dubbed Baltra, a component of the underlying bedrock as well as the ejecta from
the impact which formed the crater. The process was interrupted on August 7th
by a fault that required rebooting of the software and realignment of the antenna.
By August 10th the rover returned to normal operation, and proceeded to examine
a nearby laminated ripple in the ejecta until the 17th when it resumed its drive
toward nearby Victoria Crater. As of sol 918 (August 24, 2006), Opportunity’s
total odometry was 9,015.19 meters (5.60 miles).
Spirit completed its panoramic full color imaging of the McMurdo site, and continued
its photometric study of the surrounding rocks and seasonal changes in soils
in the vicinity of its current location. The solar panels have been providing
a steady 280 watt hours per sol and all systems are operating at peak efficiency
considering that the rover is in the depths of winter since celebrating the winter
solstice on August 7th.
Prior to Spirit's trek over Gusev Plains, Martian igneous rock analysis revealed
that Mars was covered by rocks with chemical compositions typical of rocks formed
by explosive igneous activity on Earth. Cinder, volcanic ash, and gas eruptions
which build steep sided volcanos like Mt. St. Helens and devastate surrounding
regions are typical of such activity. As a result of data yielded by Spirit,
the Gusev region has now been classified as an alkaline igneous province. Such
provinces on Earth are characterized by basalts derived from partial melting
of deep mantle rocks. This type of activity is normally associated with "Hot
Spots" in the mantle which transport fluid magma to the surface and produce
quiet eruptions characterized by lava fountains and lava flows which build broad
gentle sloping shield volcanos like those which formed the Hawaiian Islands.
This knowledge is reinforced by the presence of super–sized shield cones
like Olympus Mons which dominates the other shield volcanos of the Tharsis Region
on Mars and is the largest volcano in the Solar System.
Mercury (magnitude = - 0.4) is not visible in the evening sky until late September
because it reaches Superior Conjunction at 1 AM EDT on the 1st. It is just 0.16° from
Mars in Virgo on the 15th when both are buried in the sunset. The waxing gibbous
Moon is 3° south of Neptune (7.8) in Aquarius at 6 PM EDT on the 5th. Then
the Full Moon passes Uranus (5.7) in Aquarius at 11 AM EDT on the 7th, 17 hours
after the opposition of Uranus. The waning crescent Moon will pass within 2° of
Saturn at 11 PM EDT on September 18th, and a barely perceptible crescent will
be highlighted by nearby (1°) Venus on the 21st, one day before New Moon.
The waxing crescent Moon visits Mercury on the 24th, right after sunset, then
is barely past Jupiter (-1.8) in Libra during the evening of the 26th.
Saturn (0.5) is 6° west of Venus (- 3.7) on the morning of September 1st
in Leo. The two planets will separate in September as Venus falls into sunrise
and Saturn rises higher in the predawn sky each day. As it falls, Venus will
pass within 1° of Regulus in Leo at 7 PM EDT on the 5th.
Pluto (magnitude 13.9), the recently reclassified "Dwarf Planet", is
in Serpens Cauda, three months past opposition in June. I wonder how Clyde Tombaugh,
the discover of Pluto, would feel about the new designation. In fact, the reclassification
of Pluto was instigated and conducted by a minority segment of the astronomical
The Perseid Meteor Shower of August 12th provided 20 to 30 meteors per hour in
better observing sites, but September has no comparable meteor showers. The Aurigids
are after moonset on the 1st and typically produce around 5 to 7 meteors per
hour and the Piscids, which average about 3 per hour, appear on the 20th before
New Moon on the 22nd. Unless one of these showers produces an unexpected outburst,
meteors will not be very abundant in September.
After the tiny and very brief reverse polarity sunspot appeared and disappeared
at the end of July, solar physicists wondered if the new Sunspot Cycle (24) was
starting. Sunspot numbers cycle over a 9-11 year period from one sunspot minimum
to the next. Some minimums are characterized by few if any sunspots, and maximums
may yield averages well over 100 sunspots. Sunspots are cooler areas on the Sun
which are darker than the surrounding hot areas comprised of upwelling hot gas
and plasma from below. Lots of spots are associated with excess solar turbulence
and magnetic disturbances probably related to greater energy production at depth.
Recent improvements in the accuracy of knowledge of past climate reveal that
maximums are linked to warmer periods on Earth.
Since each new cycle is characterized by sunspots of opposite magnetic polarity
from those of the last cycle, the appearance of a reverse polarity sunspot may
indicate that Cycle 23 has ended and 24 has started. A second and significantly
larger reverse polarity sunspot (#905) appeared on August 25th, then broke apart
by month's end, so stay tuned for further updates. The last maximum was in 2000,
and the next one, predicted to be in 2010, is expected to be larger than the
last. Since sunspot maximums are associated with more frequent explosions of
charged particles (solar wind) from the Sun which produce auroras 3 to 4 days
later, this is music to the ears of those of us who glory in the Northern Lights.
The complex geologic / hydrologic / atmospheric / biologic cycles of the Earth
surpass those of other terrestrial planets due to its larger size and mass. The
Carbon Cycle is an excellent example. As far as we know, only Venus and Mars,
the terrestrial planets which rank next in size and mass to Earth, show evidence
of a significant carbon cycle.
On Earth, carbon enters the cycle naturally via volcanic outgassing of carbon
dioxide and methane and is also contributed by comets and meteoric dust and gas.
It then enters the atmosphere and hydrosphere as CO2. If CO2 abundance in the
atmosphere is designated X, then abundance in the hydrosphere is 50X. Photosynthesis
and other processes then serve as conduits to the biosphere and soil (2.8X).
Carbon may proceed to long term storage as fossil biomass (6X) like coal and
petroleum; as seabed and lakebed sediment fixed by organic and inorganic processes
into carbonate (100,000+X) and graphitic rock; or as mantle carbon converted
into diamond! Alternatively, carbon may increase in concentration in the atmosphere,
hydrosphere, or biosphere, altering ocean processes and climate, and some may
be lost to outer space.
The atmosphere of Venus is dominated by CO2 (~200,000X). Its abundance indicates
that all of the carbon on Venus may have boiled off into the atmosphere where
it stays due to the runaway Greenhouse Effect on the planet. The miniscule amount
of CO2 in the atmosphere of Mars and relatively small amount in the polar caps
indicate that carbon on Mars may be stored in ground ice, sediments, and rocks,
awaiting a warmer day for entrance into the surface environment.
September's Full Moon occurs in eastern Aquarius near the border with Aries.
It is at 2:42 PM EDT on September 7th and will by partially eclipsed by the Earth.
Residents along the periphery of the South Atlantic will enjoy an Annular Solar
Eclipse during New Moon on the 22nd. September's Full Moon is called the "Fruit
Moon." The "Harvest Moon" is the full moon which is closest to
the Autumnal Equinox on Saturday the 23rd at 12:06 AM EDT. It is 15 days, 9 hours
and 43 minutes after the Full Moon. The next Full Moon is 14 days, 23 hours and
7 minutes after the equinox so October wins the honor of hosting the "Harvest
Moon" in 2006 by a margin of 10 hours and 40 minutes.
Earth's axis is tilted relative to a line perpendicular to it's orbit by 23.5°,
a value that varies from 21.5° to 24.5° over 40,000 years. At the Autumnal
Equinox the axis leans in the direction that Earth is orbiting and is perpendicular
to the line between the Earth and the Sun. The Sun is directly above the Earth's
equator so daytime and nighttime hours are equal everywhere on Earth. As we orbit
beyond the equinox point, the axis leans progressively farther away from the
Sun causing cooling in the northern hemisphere even though the Earth is approaching
its perihelion in January when it is closest to the Sun.