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April Skies


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April Skies

by Dick Cookman

04/4/2013

Highlights: Comet Journal, Martian Landers, Meteor Showers, Impactors, Planet Plotting, April Moon

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

Comet Journal

Comet C/2011 L4 (PanSTARRS) in Andromeda is above the plane of Earth's orbit between the Earth and Sun and rapidly ascending higher. After peaking at 1st magnitude (-0.5) on March 10, it has diminished to 4th magnitude and appears to quiver like a pale Luna Moth as its light passes through the wavering atmosphere on the northwestern horizon right after sunset. It will move northward through Cassiopeia in April and drop to 6th magnitude by month's end.

The comet will move through northern skies to Bootes and drop to 11th magnitude by summer's end, after which it will spiral upward through Corona Borealis and Hercules for the next two years retreating to the Oort Cloud from which it came.

As Comet PanSTARRS retreated, C/2012 F6 (Lemmon) moved into southern Aquarius in late March and peaked at 5th magnitude for observers in the southern hemisphere when at perihelion on March 24th. It will continue northward into Pisces in April and will dim to 6th magnitude as its path through the sky in May and early June mimics that of PanSTARRS. Both comets have similar orbits as each is now ascending above the plane of the Solar System and is destined to return to the Oort Belt which is actually a collection of icy planetesimals located on the edge of the Solar System about one light year from the Sun. They are arrayed in a spherical cloud with a central disk paralleling the plane of the ecliptic.

Comet C/2012 S1 (ISON) is still circling through western Gemini at 14th magnitude. The comet is approaching the outer asteroid belt close to the plane of the ecliptic and has traversed almost 30% of the distance from the orbit of Jupiter to the orbit of Mars. It is still on track to be a super comet at the end of the year if it successfully slips through the outer and inner asteroid belts as it orbits into the inner Solar System. Observers remain optimistic about projections of naked eye visibility in October and a spectacular apparition in November and December but are aware that obstacles include collision with or orbit alteration by objects on the inbound path and disruption when grazing the Sun's corona on Nov. 28th.

Martian Landers

On Feb. 28 a computer glitch on Curiosity's main computer prompted the engineers to switch the rover to a redundant computer. Full science operations were delayed until March 21st when weather monitoring was resumed. On the 23rd, another portion of the powder from the sample drilled in February was delivered to the Sample Analysis at Mars (SAM) instrument which then began analysis. From April 4th to May 1st, Curiosity will not conduct additional science activities due to the upcoming Mars Opposition when the planet is 234 million miles away from Earth, and the Sun is between Earth and Mars interfering with radio communication.

From Sol 3226 (Feb. 20, 2013) through 3260 (March 26, 2013), Opportunity traveled 70 meters on Cape York. It started with a trip of 36.5 meters) to the southeast to examine a rock target (Big Nickel). Then a series of difficulties developed. First, the rover was unable to reach an observation site due to wheel slippage. This was followed by failure of the Flash memory system on the 28th. The ensuing reset of the memory and clearing of the resulting X-band fault on the high-gain antenna was completed by March 4th and Opportunity headed 33 meters due south on Sol 3240 (March 5, 2013), to a location called Kirkwood which had been visited before. In-situ (contact) science on the newberries at this location was then completed by March 21st (Sol 3255) and the rover drove 25 meters north to Big Nickel, the final in-situ investigation area at Matijevic Hill. Solar array energy production averaged approximately 500 watt hours per day during the period but bumped up to 590 watt hours on the 26th due to favorable dust cleaning event by a Martian zephyr.

Meteor Showers

The Lyrid Meteors on the 22nd which have averaged 18 meteors/hour in the past provide the best shower in April. The meteors will hide in the glare from the waxing gibbous Moon until the brief interval between moonset at 4 AM EDT and dawn. Then observers can enjoy the peak of the shower as we plunge head on into the river of comet debris from Comet Thatcher (C/ 1861 G1) which is due to return in 2276.

Impactors

The 50 foot diameter Russian Fireball that exploded 10 miles above the surface on Feb. 15th is an example of the Apollo Asteroids which orbit the Sun on very elliptical orbits passing through the Asteroid Belt at aphelion and between the Earth and Sun at perihelion, crossing Earth's orbit in the process. According to the Minor Planet Center, there are 240 known Apollo Asteroids larger than 1 kilometer in diameter and about 80 million which are at least as large as a house.

After geologist Gene Shoemaker completed his pHD dissertation on the Barringer Meteor Crater in Arizona in 1960, he and his wife Carolyn researched astroblemes which were previously thought to be volcanic in origin. They concluded that comet and meteoric impacts were more likely explanations. In 1969 they started a search for asteroids which crossed Earth's orbit and essentially founded the field of astrogeology. As the scientific community adopted their concepts, dozens and dozens of impact site discoveries were made by the Shoemakers and other geologists and planetary scientists.

Forty four impact sites of 20+ kilometer diameter are listed in the Earth Impact database at the Planetary and Space Science Centre at the University of New Brunswick which lists a total of 183 confirmed sites. Typical impact crater diameters range from 10 to 20 times the impactor diameter. The Barringer Crater is approximately 1 km in diameter and was probably caused by a 50 to 100 meter diameter impactor generating the energy equivalent of 200 megatons of TNT. Frequency of collisions with Earth of objects of this size is one every 1000 years. The Chicxulub event which participated in the demise of the dinosaurs resulted in a 180 km. diameter crater created by an impact with estimated energy of 100 million mt.

Planet Plotting

Mercury (+0.2) and Neptune (+7.9) in Aquarius are barely visible with binoculars in the predawn skies in early April and Uranus (+5.9) in Pisces may appear as Mercury drops into the glow of sunrise in the latter part of the month.

Jupiter (-2.1) in Taurus dominates the southwestern evening sky until it sets before midnight in early April and in mid-evening at the end of the month when Venus (-3.9) makes its appearance on the northwestern horizon after sunset in Aries. Look for the close proximity of the waxing Crescent Moon, Jupiter, Aldebaran & the Hyades in Taurus, and the Pleiades on the evenings of April 11 - 14.

Saturn is at opposition on the 28th when it is visible throughout the night and at its brightest for 2013. Its rings are tilted upward about 18° to our line of sight, presenting a spectacular image.

Mars and Venus have a conjunction on the 7th which is not visible as both buried deep in the glow of sunrise. The conjunction between Uranus and Mercury on the 20th will suffer a similar fate.

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PlanetConstellationMagnitudePlanet Passages
SunPisces, Aries-26.8New Moon, 4/10, 5:35AM EDT
MercuryAquarius, Pisces+0.2 to -0.9Uranus 1.80°NNW, 4/20, 6AM EDT
VenusPisces, Aries-3.9Mars 0.64°NNW, .4/7, 1AM EDT
MarsPisces, Aries+1.2Venus 0.64°SSE, 4/7, 1AM EDT, Solar Conjunction, .4/17, 8PM EDT
JupiiterTaurus-2.1 to -2.0 
SaturnLibra+0.3 to +0.1Solar Opposition, .4/28, 4AM EDT
UranusPisces+5.9Mercury 1.80°SSE, .4/20, 6AM EDT
NeptuneAquarius+7.9 

April Moon

The New Moon of April 10th at 5:35AM EDT marks the start of Lunation 1117 which is 29.62 days long and ends with the New Moon of May 9th.

April's Full Moon at 3:57PM EDT on the 25th is called the "Egg, Grass, Easter" or "Paschal Moon." Colonial Americans called it the "Planter's Moon" and the Celts referred to it as the "Growing Moon." Chinese call it the "Peony" Moon and medieval English named it the "Seed Moon." Northern Michigan Anishnaabe (Chippewa and Ojibwe) know it as the "Iskigamizige-giizis(oog)" (Broken Snowshoe Moon). The South Pacific skies will host a partial Eclipse during Full Moon.

The Moon was at perigee (closest to Earth) at midnight on March 31st and reaches it again on April 27th at 3:52PM EDT. It was at 57.62 earth radii on March 31st and will be slightly farther at 56.8 Earth radii (225,103 mi.) on the 27th. On the 15th the Moon is at apogee and will be 251,570 miles away or at a distance of 63.48 Earth radii.

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Planet Constellation Magnitude Moon Passage Moon Phase/Age
SunPisces-26.85:35 AM EDT. 4/10New ~ 0 days
MercuryAquarius+0.17.0°N, 6AM EDT, 4/8Waning Crescent ~ 27.02 days
VenusPisces-3.93.2°N, 3PM EDT, 4/10Waning Crescent ~ 0.39 days
MarsPisces+1.22.7°N 11AM EDT, 4/10Waxing Crescent ~ 0.23 days
JupiterTaurus-2.12.0°S, 2PM EDT, 4/14Waxing Crescent ~ 4.35 days
SaturnLibra+0.14.0°S, 10PM EST, 4/25Waning Gibbous ~ 15.35 days
UranusPisces+5.93.9°NNW, 9AM EDT, 4/9Waning Crescent ~ 28.02 days
NeptuneAquarius+8.06.0°N, 9PM EDT, 4/6Waning Crescent ~ 25.02 days




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