April Calendar by Dave Mitsky

All times, unless otherwise noted, are UT (subtract 4 hours and, when appropriate, 1 calendar day for EDT)

4/2 The crescent Moon is 0.33 degree north of the center of the bright open cluster M45 (the Pleiades) at 00:00 - occultations and grazing occultations of some of M45's stars take place in eastern and central North America and the Caribbean; Daylight Saving Time begins at 7:00
4/3 Mars is 3.5 degrees south of the Moon at 19:00; maximum lunar libration of 9.6 degrees occurs at 21:00
4/5 A double shadow transit of Jupiter by the Galilean satellites Io and Ganymede begins at 9:30; Saturn is stationary in right ascension, with direct (eastward) motion to resume, at 12:00; First Quarter Moon occurs at 12:01
4/6 The Moon is 1.7 degrees south-southwest of the first magnitude star Pollux at 3:00
4/7 Mercury reaches its greatest illuminated extent (23"); Saturn is 3.8 degrees south-southwest of the Moon at 1:00; the Moon is 2.9 degrees north-northeast of the bright open cluster M44 (the Beehive Cluster) at 7:00; Mercury is at aphelion at 23:00
4/8 Mercury is at greatest western elongation (27.8 degrees) at 19:00
4/9 The Moon is 2.5 degrees north-northeast of the first magnitude star Regulus at 5:00; the Moon is at apogee, subtending 29'28" from a distance of 405,551 km, at 13:00
4/11 Minimum lunar libration of 1.6 degrees occurs at 7:00
4/12 The Moon is at the descending node (longitude 184.4 degrees) at 2:36; the Moon is at its greatest declination north (25.1 degrees) at 9:00; Venus is at the descending node of the ecliptic at 17:00
4/13 Full Moon, known as the Egg or Grass Moon, occurs at 16:40; the Moon is 0.37 degree east-northeast of the first magnitude star Spica at 18:00 - an occultation takes place in southern Asia and northern Australia
4/15 Jupiter is 4.8 degrees north-northeast of the Moon at 12:00; the equation of time is equal to 0 (i.e., sundial time and clock time are the same) at 18:00
4/16 The Galilean satellite Ganymede reappears from eclipse at 5:26; Ganymede is occulted by Jupiter at 5:36
4/17 The Moon is 0.33 degree west-southwest of the first magnitude star Antares at 8:00 - an occultation takes place in southern South America; Mars is 0.7 degree north of the center of the bright open star cluster M35 at 16:00
4/18 Venus (-4.2 magnitude) is 0.33 degree north-northwest of Uranus (5.9 magnitude) at 9:00; Venus and Uranus are separated by only 18' at 10:00; maximum lunar libration of 9.0 degrees occurs at 17:00
4/19 The Sun enters the constellation of Aries (ecliptic longitude 28.91 degrees) at 3:00
4/21 Last Quarter Moon occurs at 3:28
4/22 The peak of the Lyrid meteor shower (20/hour) occurs at 16:00; Neptune is 3.5 degrees north-northwest of the Moon at 12:00
4/24 Uranus is 1.1 degrees north-northwest of the Moon at 3:00 - an occultation takes place in southern South America, South Island New Zealand, and southeastern Australia; Venus is 0.47 degree west-northwest of the Moon at 14:00 - an occultation takes place in most of South America and southeastern West Africa
4/25 Saturn is at eastern quadrature (i.e., it is 90 degrees east of the Sun) at 1:00; minimum lunar libration of 0.4 degree occurs at 9:00; the Moon is at perigee, subtending 32'51" from a distance of 363,731 km, at 11:00; the Moon is at the ascending node (longitude 4.1 degrees) today
4/26 Mercury is 3.5 degrees south-southeast of the Moon at 5:00
4/27 New Moon (lunation 1031) occurs at 19:44
4/28 Mercury is its greatest heliocentric latitude south (-7.0 degrees) at 6:00
4/29 The Moon is 0.35 degree west-northwest of M45 at 10:00
4/30 May Eve, a cross-quarter day; Mars is at heliocentric conjunction with Saturn (heliocentric longitude 131.2 degrees) at 3:00

Times and dates for the lunar light rays predicted to occur this month are available at http://www.lunar-occultations.com/rlo/rays/rays.htm

A major lunar event occurs on April 1. Look to west about 45 minutes after sunset to see the old Moon in the new Moon's arms occult some of the stars of the Pleiades.

The planets on April 1: Mercury (0.5 magnitude, 8.8", 35% illuminated), Venus (-4.3 magnitude, 22.8", 53% illuminated), Mars (1.2 magnitude, 5.7", 91% illuminated), Jupiter (- 2.4 magnitude, 42.9", 100% illuminated), Saturn (0.1 magnitude, 19.1", 100% illuminated), Uranus (5.9 magnitude, 3.4", 100% illuminated), Neptune (7.9 magnitude, 2.2", 100% illuminated), and Pluto (13.9 magnitude, 0.1", 100% illuminated).

Morning planets: Mercury, Venus, Uranus, Neptune, and Pluto

Evening planets: Mars, Jupiter, and Saturn

For observers in the northern hemisphere, Mercury puts on a poor morning apparition this month.

Still shining brightly, Venus rapidly shrinks 6" in apparent size during April. Venus and Uranus have a close encounter of the planetary kind just before daybreak on April 18.

Mars is positioned between Beta and Zeta Tauri, the stars at the ends of the horns of Taurus, on April 1. The Red Planet is only some 5" in size as it travels eastward along the ecliptic. By April 17, it will be within 1 degree of M35 in Gemini and on April 30 it will be even closer to third magnitude Epsilon Geminorum.

Jupiter, in Libra, rises just after sunset by month's end. It lies less than 1 degree north of Zubenelgenubi on April 25. The Great Red Spot (GRS) has a new red companion, or perhaps more accurately pale pink, the result of an unexpected change in color of the white oval known as BA. Dubbed Red Junior and Red Spot Junior, it's about half the size of the GRS and is located in the South Temperate Belt. Red Junior lags behind the GRS by about an hour. In order to determine the transit times of the GRS, click on http://skyandtelescope.com/observing...icle_107_1.asp

Dimming slightly, Saturn resumes its eastward course towards M44 on April 5. After reaching quadrature on April 25, the shadow of Saturn's globe is cast farthest sidewards onto its rings, resulting in the illusion of greater depth. Titan (8.4 magnitude), Saturn's largest satellite, is directly north of the Ringed Planet on April 6 and April 22. It's due south of Saturn on April 14 and April 30.

Uranus moves 1 degree northeastward, from 1 degree east of fourth magnitude Lambda Aquarii to quite close to the sixth magnitude star 81 Aquarii, in the span of a month.

During April, Neptune resides some 2 degrees northeast of fourth magnitude Iota Capricorni.

Located in Serpens, Pluto is more easily observed in the coming months.

On the night of April 3, asteroid 4 Vesta (7.9 magnitude) passes approximately 25' north of 37 Geminorum. Vesta dims from 7.8 to 8.1 magnitude as it tracks eastward between the first magnitude star Pollux and the third magnitude star Epsilon Geminorum.

Comet 73P/Schwassmann-Wachmann 3 broke into 4 major pieces in 1995. The possibility exists that as a result the comet could brighten to as much as second magnitude in May. During April, it may glow at seventh magnitude as it passes through Corona Borealis.

Comet C/2006 A1 (Pojmansk), which displayed a dim but moderately long gas tail as it graced the eastern morning sky in early March, travels rapidly to the northeast, eventually passing through Cassiopeia.

Seventy-five binary and multiple stars for April: h4481 (Corvus); Aitken 1774, Gamma Crateris, Jacob 16, Struve 3072, h4456, Burnham 1078 (Crater); h4311, Burnham 219, N Hydrae, h4455, h4465 (Hydra); 31 Leonis, Alpha Leonis (Regulus), h2520, Struve 1417, 39 Leonis, Struve 1421, Gamma Leonis (Algieba), Otto Struve 216, 45 Leonis, Struve 1442, Struve 1447, 49 Leonis, Struve 1482, 54 Leonis, Struve 1506, Chi Leonis, 65 Leonis, Struve 1521, Struve 1527, Struve 1529, Iota Leonis, 81 Leonis, 83 Leonis, Tau Leonis, 88 Leonis, 90 Leonis, Struve 1565, Struve 1566, 93 Leonis, h1201, S Leonis (Leo); h2517, Struve 1405, Struve 1432, 33 Leo Minoris, Struve 1459, 40 Leo Minoris, Struve 1492 (Leo Minor); Struve 1401, Struve 1441, Struve 1456, Struve 1464, 35 Sextantis, 40 Sextantis, 41 Sextantis (Sextans); Struve 1402, Sturve 1415, Struve 1427, Struve 1462, Struve 1486, Struve 1495, Struve 1510, Struve 1520, Xi Ursae Majoris, Nu Ursae Majoris, Struve 1541, 57 Ursae Majoris, Struve 1544, Struve 1553, Struve 1561, Struve 1563, 65 Ursae Majoris, Otto Struve 241 (Ursa Major)

Challenge binary star for April: Gamma Sextantis

One hundred deep-sky objects for April: NGC 4024, NGC 4027 (Corvus); NGC 3511, NGC 3513, NGC 3672, NGC 3887, NGC 3892, NGC 3955, NGC 3962, NGC 3981 (Crater); NGC 3091, NGC 3109, NGC 3145, NGC 3203, NGC 3242, NGC 3309, NGC 3585, NGC 3621, NGC 3717, NGC 3904, NGC 3936 (Hydra); M65, M66, M95, M96, M105, NGC 3098, NGC 3162, NGC 3177, NGC 3185, NGC 3190, NGC 3226, NGC 3227, NGC 3300, NGC 3346, NGC 3367, NGC 3377, NGC 3384, NGC 3389, NGC 3412, NGC 3437, NGC 3489, NGC 3495, NGC 3507, NGC 3521, NGC 3593, NGC 3607, NGC 3608, NGC 3626, NGC 3628, NGC 3640, NGC 3646, NGC 3655, NGC 3681, NGC 3684, NGC 3686, NGC 3691, NGC 3705, NGC 3810, NGC 3842, NGC 3872, NGC 3900, NGC 4008 (Leo); NGC 3245, NGC 3254, NGC 3277, NGC 3294, NGC 3344, NGC 3414, NGC 3432, NGC 3486, NGC 3504 (Leo Minor); NGC 2990, NGC 3044, NGC 3055, NGC 3115, NGC 3156, NGC 3166, NGC 3169, NGC 3246, NGC 3423 (Sextans); IC 750, M97, M108, M109, NGC 3079, NGC 3184, NGC 3198, NGC 3310, NGC 3359, NGC 3610, NGC 3665, NGC 3675, NGC 3738, NGC 3877, NGC 3898, NGC 3941, NGC 3953, NGC 3998, NGC 4026 (Ursa Major)

Challenge deep-sky object for April: Leo I (Leo)

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