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April 2017 Skies
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by Dick Cookman
Highlights: Comet Journal, Martian Landers, Meteor Showers, Planet Plotting, April Moon
Focus Constellations: Leo, Cancer, Gemini, Taurus, Auriga, Perseus, Cassiopeia, Cepheus, Draco, Hercules, Bootes, Ursa Minor, Ursa Major, Camelopardalis, Lynx
The brightest comet of April is 41P/Tuttle-Giacobini-Kresak which moves through Draco. At almost 6th magnitude, it may reach naked eye visibility at 5th magnitude as it approaches and passes perihelion on the 13th. By the end of the month, it will arrive in Hercules then trace a path along the border of Hercules and Lyra in early May.
C/2017 E4 (Lovejoy) is in Pegasus in the morning sky and moves through Andromeda by month's end. It is at 7th magnitude and may reach 6th magnitude near perihelion on the 23rd. It is expected to enter Taurus by the end of May.
C/2015 ER61 (PanSTARRS) moves through Capricornus and Aquarius in April. It is approaching 7th magnitude and is expected to remain at that level until it passes through perihelion on May 9th.
Comet V2 Johnson is in western Hercules at 9th magnitude. It brightens and circles into Bootes in April and May as it approaches perihelion in early June.
"Perseverance Valley" is the next target for investigation for Opportunity. It was about a half mile south of the rover's location on the inside of the rim of the 14 mile wide Endeavor Crater on Sol 4651 (Feb. 22, 2017). The water or debris flow carved valley cuts through the crater's rim and is about 600 feet long. The rover covered about 25% of the half mile by Sol 4677 (Mar. 21, 2017), despite dealing with a dust storm a few hundred kilometers away which increased atmospheric opacity, reducing solar panel output from earlier levels of 484 watt hours per sol. The resulting atmospheric turbulence in the vicinity produced dust removal from the solar panels, increasing output from a low of 366 to 423 watt hours per sol. Surface targets studied during the interval include "Boonville" and "Waverly". Panoramic imaging of the area features/landscapes was also completed. Total odometry is 27.48 miles (44.23 km).
Curiosity is ascending the flank of Mt. Sharp, Gale Crater's central peak. A 3.5 to 3.0 billion year old mudstone observed in January displays slabs with polygonal ridges of harder material. They appear to represent mudcrack fillings, indicating a period of drying conditions during which windblown sediment filled desiccation cracks in the muds of an ancient lake bottom. Other cracks are filled with younger calcium sulfate veins produced as ground water percolated through fractured rock layers formed from lithified mud. This combination is indicative of changing environments characterized by earlier humid conditions forming a bed of a lake. It dried up during later arid weather characterized by windblown sediments. Burial of sediments supplied pressure for lithification and fracturing. This was followed by resumption of humid conditions providing underground water from which calcium sulfate veins crystallized in fractures.
The absence of calcium carbonate in the veins suggests a dearth of carbon dioxide or methane in the environments of the time leading to the probability that greenhouse effects were minimal. This, in combination with the distance of Mars from an ancient Sun with 66% as much output, indicates existence of freezing conditions which obviate previously collected evidence of flowing and standing water in the rock record examined by all of the rovers. Mars again presents us with a paradox providing planetary scientists with abundant fodder for future study.
The best meteor shower in April is the Lyrids on the 22nd. The Lyrids often reach 25 to 30 meteors per hour in dark skies, but the waning Crescent Moon may interfere with glare in the eastern sky before sunrise. In 1982, meteor count reached 90 per hour in some locales. The shower is composed of debris left by former passages of Comet Thatcher through the inner Solar System. The best viewing time is at 4AM EDT when we are on Earth's leading face as it plunges through the debris stream stretching across our orbit.
Morning planets in April include Venus (-4.2 to -4.5) in Pisces and Saturn (+0.4 to +0.2) in Sagittarius. Venus was at inferior conjunction on Mar. 25th and is low in the eastern sky at dawn early in April. Its waxing crescent will grow as the planet rises higher in the predawn skies and brightens during April and approaches maximum western elongation in June. In April, Saturn shines brightly in the southern and southeastern sky in Sagittarius before sunrise. It is gradually getting brighter as it approaches opposition in June. Neptune (+7.9) was at conjunction with the Sun on March 1st, after which it appeared in Aquarius in the morning sky where it will remain until opposition in September.
Mercury (-0.7 to +5.6 to +2.3), Mars (+1.5 to +1.6), and Jupiter (-2.5 to -2.3) are the brightest evening planets. Mercury travels from maximum eastern elongation on the 1st to inferior conjunction on the 20th, after which it is a morning planet in May. The 1st week of April is one of its best apparitions of 2017 when Mercury is low in the west in Pisces after sunset. It disappears into solar glare as it approaches inferior conjunction and will be separated from Uranus by 0.09° in Pisces on the 28th, when they may be seen in the east before sunrise. Mars (+1.3 to +1.5) is in early evening western skies in Aries and Taurus. By the 20th, it can be seen about 4 degrees from the Pleiades cluster. Jupiter (-2.5 to -2.3) is 4 times brighter than nearby Spica in Virgo and is at its brightest for 2017 when reaching opposition on the 7th when it rises at sunset and sets at sunrise. Uranus (+5.9) in Pisces reaches solar conjunction on the 14th and is a difficult target in April.
Mercury (-0.7 to +5.6 to +2.3), Mars (+1.5 to +1.6), and Jupiter (-2.5 to -2.3) are the brightest evening planets. Mercury travels from maximum eastern elongation on the 1st to inferior conjunction on the 20th, after which it is a morning planet in May. The 1st week of April is one of its best apparitions of 2017 when Mercury is low in the west in Pisces after sunset. It disappears into solar glare as it approaches inferior conjunction and will be separated from Uranus by 0.09° in Pisces on the 28th, when they may be seen in the east before sunrise. Mars (+1.3 to +1.5) is in early evening western skies in Aries and Taurus. By the 20th, it can be seen about 4 degrees from the Pleiades cluster. Jupiter (-2.5 to -2.3) is 4 times brighter than nearby Spica in Virgo and is at its brightest for 2017 when reaching opposition on the 7th as it rises at sunset and sets at sunrise. Uranus (+5.9) in Pisces reaches solar conjunction on the 14th and is a difficult target in April.
|Sun||Pisces, Aries, Taurus||-26.8||New Moon, 3/27 10:57AM EDT|
|Mercury||Pisces||-0.2||Max. East Elongation, 4/1, 6AM EDT|
|Mercury||Aries||+5.6||Inferior Conjunction 4/20, 2AM EDT|
|Mercury||Pisces||+2.3||Uranus, 0.09°NW, 4/28, 8AM EDT|
|Venus||Pisces||-4.2 to -4.5|
|Mars||Aries, Taurus||+1.5 to +1.6|
|Jupiter||Virgo||-2.5 to -2.3||Opposition 4/7, 6AM EDT|
|Saturn||Sagittarius||+0.4 to +0.2|
|Uranus||Pisces||+5.9||Solar Conjunction 4/14, 2AM EDT|
|Uranus||Pisces||+5.9||Mercury, 0.09°SE, 4/28, 8AM EDT|
New Moon of April 26th at 8:17AM EDT is the beginning of Lunation 1167 which ends 29.39 days later with the New Moon of May 25th at 3:45PM EDT.
The Full Moon of April in Leo occurs at 2:08AM EDT on the 11th. The April Moon is called the “Planter's Moon”, a name also utilized by Colonial Americans. It is also called the "Pink Moon" as some Native Americans related it to the blooming of wild ground phlox during April. To the Celts it was the “Growing Moon”, and the Chinese refer to it as the “Peony Moon”. Medieval English thought of it as the “Seed Moon”, and the Anishinaabe (Odawa and Ojibwe) people of northern Michigan recognize it as "Iskigamizige-giizis" (Sugarbushing Moon).
Lunar perigee (closest to Earth) is 223,273 miles or 56.34 Earth radii on the 27th at 12:14PM EDT. Apogee position in orbit (maximum orbital distance) is at 251,952 miles (63.57 Earth radii) from Earth on the 15th at 6AM EDT.
Cecil Adams’ scenarios for an Earth sans Moon (part 1):
Situation #1: "No more big tides to enhance surfing, etc. Tides wouldn't disappear entirely, since the Sun would continue to tug on the oceans, causing high tides of diminished amplitude at noon and midnight. But, as one early consultant pointed out, it's a safe bet the bottom would fall out of the tourist trade in the Bay of Fundy, noted for its tidal extremes."
Situation #2: "Dogs would have to bay at, I dunno, Alpha Centauri or Sirius."
Situation #3: "Much darker at night. Duh, you say, but a fair amount of nocturnal activity among the lower orders is pegged to moonlight."
Dick Cookman's Explanations:
#1 The intensity of tides varies with storms and configuration of coastlines which may focus and intensify tidal height. Gravitational effects of the Sun & Moon cause tides and influence their size based on solar and lunar distance. Intensity depends not only on mass and distance of each body but also on distances to the near and far sides of Earth. The Moon attracts the near side of Earth more than the far side, stretching the planet into a football shape. The ocean is stretched more because it is more fluid than earth, creating high tides on the near and far sides. Differences in gravitational pull compared to lunar distance & size are larger than for the Sun making lunar contributions to tides more than twice as great.
#2 My hypothesis is that dogs aren't howling at the Moon, but at each other to establish territory and inquire as to position of other dogs. I think that they howl under full moons because the landscape is lit up, attracting their attention.
#3 Animals (and plants & microbes) are greatly influenced by nighttime light as they sleep, hunt, gather, and flee. This influence is not limited to light intensity but also is affected by color and wavelength. Moonlight is a significant contributor which impacts behavior and success of undertakings as it changes with lunar position and phase. Human intervention drastically complicates these conditions as light pollution invades habitats.
|Planet||Constellation||Magnitude||Moon Passage||Moon Phase/Age|
|Sun||Aquarius||-26.8||8:17AM EDT, 4/26||New ~ 0 days|
|Mercury||Pisces||+2.5||4.3°SSE, 2PM EDT, 4/25||Waning Crescent ~28.63 days|
|Venus||Pisces||-4.5||4.9°SSE, 5PM EDT, 4/23||Waning Crescent ~26.75 days|
|Mars||Taurus||+1.6||5.7°S, 5AM EDT, 4/28||Waxing Crescent ~1.86 days|
|Jupiter||Virgo||-2.5||2.3°NNE, 6PM EDT, 4/10||Waxing Gibbous ~13.79 days|
|Saturn||Sagittarius||+0.3||2.1°NNE, 7PM EDT, 4/16||Waning Gibbous ~ 19.83 days|
|Uranus||Pisces||+5.9||3.5°SSE, 2PM EDT, 4/25||Waning Crescent ~28.63 days|
|Neptune||Aquarius||+7.9||0.21°SE, 4PM EDT, 4/22||Waning Crescent ~27.71 days|
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