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The Night Sky of April

Dr. Wayne Wooten
Professor of Astronomy

For April 2017, the Moon will be first quarter on April 3rd. The waxing gibbous moon passes two degrees north of Jupiter on March 10. The Full Moon, the Paschal Moon following the Vernal Equinox, is on March 12, and sets the following Sunday as the date for Easter this year. On Easter morning, the Waning gibbous moon is three degrees north of Saturn in the morning sky. The third quarter moon is April 19th, and the waning crescent moon passes five degrees south of brilliant Venus in the dawn sky on April 23rd. The moon is new on April 26th; only four more new moons until totality on August 21st! The waxing crescent moon passes six degrees south of Mars on April 29th.

Mercury is well placed for evening viewing as April begins, reaching greatest eastern elongation of 19 degrees east of the Sun on April 1st. But by the next week, it retrogrades into the sunís glare. Venus passed between us and the sun on March 25th, and quickly emerges into the dawn sky in early April. It reaches greatest brilliancy in the dawn at monthís end. It appears as a very thin crescent in early April, but as it gets farther west of the Sun each morning, it shrinks in size but appears more fully lit. Mars is about to be lost in the Sunís glare, setting earlier in the SW each evening.

April 2017 belongs to Jupiter. It reaches opposition on April 7th, with the bright star Spica in Virgo to the lower left of it. With a small telescope, its four largest Galilean moons are visible in a row around its equator. Our photo this months is a spectacular shot of the bright moon Europa coming onto Jupiterís disk while its black shadow is about to leave the opposite limb, and it is typical of the detail you can now get with smart phones at the eyepieces of many amateur scopes!


Europa transiting Jupiter's face

Saturn rises in the SE about midnight as April begins, and reaching opposition on June 15th. The ringed wonder is at its best in the east north of bright red Antares in Scorpius, with brighter red Mars to the upper right of them. The most beautiful object in the sky. When viewed with a telescope, the rings are open 27 degrees and double the planetís disk brightness. This year Saturn is at summer solstice, with the rings most open. Note the big moon Titan and several smaller moons fall on either side of the most beautiful telescopic sight in the sky.

Yellow Capella, a giant star the same temperature and color as our much smaller Sun, dominates the northwestern sky. It is part of the pentagon on stars making up Auriga, the Charioteer (think Ben Hur). Several nice binocular Messier open clusters are found in the winter milky way here. East of Auriga, the twins, Castor and Pollux highlight the Gemini. South of Gemini, Orion is the most familiar winter constellation, dominating the southern sky at dusk. The reddish supergiant Betelgeuse marks his eastern shoulder, while blue-white supergiant Rigel stands opposite on his west knee. Just south of the belt, hanging like a sword downward, is M-42, the Great Nebula of Orion, an outstanding binocular and telescopic stellar nursery. The bright diamond of four stars that light it up are the trapezium cluster, one of the finest sights in a telescope. In the east are the hunterís two faithful companions, Canis major and minor. Procyon is the bright star in the little dog, and rises minutes before Sirius, the brightest star in the sky. At 8 light years distance, Sirius is the closest star we can easily see with the naked eye.

To the northeast, look for the Big Dipper rising, with the top two stars of the bowl, the pointers, giving you a line to find Polaris, the Pole Star. Look for Mizar-Alcor, a nice naked eye double star, in the bend of the big dipperís handle. Take the pointers at the front of the dipperís bowl south instead to the head of Leo, looking much like the profile of the famed Sphinx. The bright star at the Lionís heart is Regulus, the "regal star".

Now take the curved handle of the Big Dipper, and follow the arc SE to bright orange Arcturus, the brightest star of the spring sky. Recent studies of its motion link it to the Sagittarius Dwarf Galaxy, a companion of our Milky Way being tidally disrupted and spilling its stars above and below the plane of the Milky Way, much like dust falling away from a decomposing comet nucleus. So this brightest star of Bootes the Bear Driver is apparently a refugee from another galaxy!

Now spike south to Spica, the blue-white gem in Virgo rising in the SE. Mars lies a little to the west of Spica in April, and is much brighter than anything else in the SE evening sky at opposition this month. Virgo is home to many galaxies, as we look away from the obscuring gas and dust in the plane of the Milky Way into deep space. To the southwest of Spica is the four sided Crow, Corvus.

To the ancient Greeks, Spica was associated with Persephone, daughter of Ceres, goddess of the harvest. She was abducted by her suitor Pluto, carried down to Hades (going to Hell for a honeymoon!) and when Jupiter worked out a compromise between the newlyweds and the angry mother-in-law, the agreement dictated Persephone come back to the earthís surface for six months of the year, and Mama Ceres was again placated, and the crops could grow again. As you see Spica rising in the SE, it is time to "plant your peas", and six months from now, when Spica again disappears in the sunís glare in the SW, you need to "get your corn in the crib"Ö.so was set our calendar of planting and harvesting in antiquity. In the arms of Virgo is a rich harvest of galaxies for modern astronomers.

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