April Celestial Calendar by Dave Mitsky
All times, unless otherwise noted, are UT (subtract four hours and, when appropriate, one calendar day for EDT)
4/1 The Moon is at apogee, subtending 29' 28'' from a distance of 405,577 kilometers (252,014 miles), at 0:14; a double Galilean shadow transit (Europa’s shadow precedes Ganymede’s shadow) begins at 11:54
4/2 The Moon is 2.6 degrees south-southeast of Venus at 7:00; Mercury (magnitude +0.8) is 0.4 degree north of Neptune (magnitude +8.0) at 19:00; the Moon is 4 degrees south of Mercury at 23:00
4/3 The Moon, Mercury, and Neptune lie within a circle with a diameter 3.4 degrees at 1:00; the Moon is 3.1 degrees south-southeast of Neptune at 2:00; the Moon is 3.4 degrees south-southeast of Mercury at 2:00
4/5 New Moon (lunation 1191) occurs at 8:50; asteroid 7 Iris (magnitude +9.4) is at opposition at 9:00
4/6 The Moon is 4.5 degrees south-southeast of Uranus at 17:00
4/8 The dwarf planet/asteroid 1 Ceres is stationary at 21:00; the Moon is 8.0 degrees south-southeast of the bright open cluster M45 (the Pleiades or Subaru) in Taurus at 23:00
4/9 The Moon is 4.6 degrees south-southeast of Mars at 10:00; the Moon is 2.1 degrees north of the first-magnitude star Aldebaran (Alpha Tauri), at 16:00
4/10 Asteroid 2 Pallas (magnitude +7.9) is at opposition at 1:00; Mercury, Venus, and Neptune lie within a circle with a diameter of 5.2 degrees at 5:00; Venus (magnitude -3.9) is 0.3 degree south-southeast of Neptune (magnitude +8.0) at 7:00
4/11 Mercury is at greatest western elongation (28.0 degrees) at 20:00
4/12 The Lunar X (also known as the Werner or Purbach Cross), an X-shaped clair-obscure illumination effect involving various rims and ridges between the craters La Caille, Blanchinus, and Purbach, is predicted to be fully formed at 4:10; the Moon at ascending node (longitude 112.0 degrees) at 18:00; First Quarter Moon occurs at 19:06; the Moon is 6.6 degrees south of first-magnitude star Pollux (Beta Geminorum) at 22:00
4/13 The Moon lies within the bright open cluster M44 (the Beehive Cluster or Praesepe) in Cancer at 21:00
4/14 Mars is 6.5 degrees north of Aldebaran at 1:00; the Moon is 2.6 degrees north-northeast of the first-magnitude star Regulus (Alpha Leonis) at 10:00; the equation of time equals 0 at 22:00
4/16 Mercury (magnitude +0.2) is 4.3 degrees east of Venus (magnitude -3.9) at 20:00; the Moon is at perigee, subtending 32' 49'' from a distance of 364,205 kilometers (226,306 miles), at 22:05
4/18 Venus is at aphelion (0.7282 a.u. from the Sun) at 2:00
4/19 The Moon is 7.1 degrees north-northeast of the first-magnitude star Spica (Alpha Virginis), at 3:00; the Sun enters Aries (longitude 29.1 degrees on the ecliptic) at 11:00; Full Moon, known as the Egg or Grass Moon, occurs at 11:12
4/20 The Sun is at longitude 30 degrees at 9:00
4/21 The Moon is 7.9 degrees north-northeast of the first-magnitude star Antares (Alpha Scorpii) at 11:00
4/22 Uranus is in conjunction with the Sun at 23:00
4/23 The peak of the Lyrid meteor shower (20 per hour) is predicted to occur at 0:00; the Moon is 1.6 degrees north of Jupiter at 12:00
4/25 The Moon is 0.4 degree south of Saturn, with an occultation taking place in western South America, New Zealand, and eastern Australia, at 14:00; the Moon is at the descending node (longitude 290.7 degrees) at 15:00; the Moon is 0.1 degree north of Pluto, with an occultation taking place in northwestern Polynesia, southeastern Micronesia, Melanesia, Australia, Indonesia, and Sri Lanka, at 20:00
4/26 Last Quarter Moon occurs at 22:18
4/28 The Curtiss Cross, an X-shaped clair-obscure illumination effect located between the craters Parry and Gambart, is predicted to be visible at 7:57; the Moon is at apogee, subtending 29' 32'' from a distance of 404,582 kilometers (251,396 miles), at 18:20
4/30 Mercury is at its greatest heliocentric latitude south today; Saturn is stationary, with retrograde (westward) motion to begin, at 2:00; the Moon is 3.3 degrees south-southeast of Neptune at 11:00
Christiaan Huygens (1629-1695) was born this month.
Charles Messier discovered the open cluster M50 in Monoceros on April 5, 1772. Charles Messier discovered the spiral galaxy M58 in Virgo on April 15, 1772. Johann Koehler discovered the elliptical galaxies M59 and M60 in Virgo on April 11, 1779. Caroline Herschel discovered C/1790 H1 (Herschel) on April 18, 1790. The first photograph of the Sun was taken on April 2, 1845. The first radar signal was bounced off of the Sun on April 7, 1959. The Hubble Space Telescope was placed in orbit on April 25, 1990. The Compton Gamma Ray Observatory achieved orbit on April 7, 1991.
The Lyrid meteor shower peaks on the night of April 22nd/April 23rd. Comet C/1861 G1 (Thatcher) is responsible for the Lyrids. A typical zenithal hourly rate is about 20 meteors per hour but short outbursts have occurred occasionally. The radiant lies between the Keystone of Hercules and Lyra. Unfortunately, a bright waning gibbous Moon will compromise the Lyrids this year, reducing counts to perhaps five per hour. For more on this year’s Lyrids, see https://earthsky.org/?p=4478 and https://www.skyandte...howers-in-2019/
Information on Iridium flares and passes of the ISS, the Tiangong-2, the USAF’s X-37B, the HST, and other satellites can be found at http://www.heavens-above.com/
The Moon is 25.2 days old, is illuminated 17.9%, subtends 29.0', and is located in Capricornus at 0:00 UT on April 1st. The Moon is at its greatest northern declination of +22.0 degrees on April 12th and its greatest southern declination of -22.1 degrees on April 25th. Longitudinal libration is at a maximum of +6.1 degrees on April 23rd and a minimum of -5.7 degrees on April 10th. Latitudinal libration is at a maximum of +6.6 degrees on April 6th and a minimum of -6.5 degrees on April 19th. The Moon is at apogee on April 1st (at a distance 63.59 Earth-radii) and April 28th (at a distance 63.43 Earth-radii) and at perigee on April 16th (at a distance of 57.10 Earth-radii). New Moon occurs on April 5th. The waning gibbous Moon occults Saturn and Pluto on April 25th from certain parts of the world. Consult http://www.lunar-occ...ota/iotandx.htm for information on occultation events. Visit http://saberdoesthes...does-the-stars/ for tips on spotting extreme crescent Moons. Click on http://www.calendar-...ndar/2019/april for an April lunar calendar. Times and dates for the lunar light rays predicted to occur this month are available at http://www.lunar-occ...o/rays/rays.htm
The Sun is located in Pisces on April 1. It enters Aries on April 19th.
Brightness, apparent size, illumination, distance from the Earth in astronomical units, and location data for the planets and Pluto on April 1: Mercury (0.8, 9.4", 29% illuminated, 0.72 a.u., Aquarius), Venus (-3.9, 13.1", 81% illuminated, 1.27 a.u., Aquarius), Mars (+1.4. magnitude, 4.6", 94% illuminated, 2.02 a.u., Taurus), Jupiter (-2.2 magnitude, 39.8", 99% illuminated, 4.95 a.u., Ophiuchus), Saturn (+0.6 magnitude, 16.4", 100% illuminated, 10.16 a.u., Sagittarius), Uranus (+5.9 magnitude, 3.4", 100% illuminated, 20.85 a.u. on April 16th, Aries), Neptune (+7.9 magnitude, 2.2", 100% illuminated, 30.72 a.u. on April 16th, Aquarius), and Pluto (+14.3 magnitude, 0.1", 100% illuminated, 33.72 a.u. on April 16th, Sagittarius).
Mars and Uranus are located in the west in the evening. Mercury, Venus, and Neptune can be found in the east, Saturn in the southeast, and Jupiter in the south in the morning sky.
Observers in the southern hemisphere are favored during the current morning apparition of Mercury. Mercury has a close conjunction with Neptune on April 2nd. The speediest planet reaches aphelion on April 10th and is at greatest western elongation on April 11th. Mercury and Venus are approximately ten degrees apart on April 1st but that distance decreases fairly rapidly. The two planets are in quasi-conjunction, a pairing with a separation of less than five degrees, on April 16th. This will be the first quasi-conjunction of Mercury and Venus in nearly three years.
On the first day of April, Venus rises at approximately 5:30 a.m. local daylight time. On April 2nd, the waning gibbous Moon passes three degrees to the south of the waxing gibbous Venus. Venus joins Mercury in a quasi-conjunction on April 16th.
As the month begins, Mars sets more than four hours after sunset. It fades from magnitude +1.4 to +1.6 and shrinks to just 4.2 arc seconds by the end of April. The Red Planet passes between the large open clusters Melotte 25 (the Hyades) and M45 (the Pleiades) during the first week of April. It lies three degrees south of M45 on April 1st. On April 8th, a waxing crescent Moon lies six degrees south of Mars and eight degrees west of Aldebaran. The Red Planet passes seven degrees north of Aldebaran on April 16th and crosses the sixth-magnitude open cluster NGC 1746 ten days later.
Jupiter increases in brightness from magnitude -2.2 to magnitude -2.4 and in apparent diameter from 39.8 to 43.4 arc seconds during April. As the month begins, Jupiter rises just before 1:30 a.m. local daylight time. On April 10th, Jupiter reaches its first stationary point. Four months of retrograde or western motion will follow. A waning gibbous Moon passes within two degrees of Jupiter on the morning of April 23rd. The Galilean satellite Io undergoes shadow transits starting at 3:25 a.m. EDT (7:25 UT) on April 2nd, 5:19 a.m. EDT (9:19 UT) on April 9th, 1:41 a.m. EDT (5:41 UT) on April 18th, and 3:34 a.m. EDT (7:34 UT) on April 25th. On April 26th, Europa’s shadow first falls on Jupiter at 3:33 a.m. EDT (7:33 UT). Ganymede emerges from eclipse 22 arc minutes west-southwest of Jupiter’s limb and 26 arc minutes south of Europa beginning at 4:02 a.m. EDT (8:02 UT) on April 12th. Since Jupiter is currently inclined three degrees with respect to the Earth, Callisto, the most distant of the Galilean satellites, does not appear to cross the planet’s disk. It is near Jupiter’s south pole on April 6th and near its north pole at dawn on April 14th. Data on other Galilean satellite events is available at http://www.skyandtel...watching-tools/ and page 51 of the April 2019 issue of Sky & Telescope. For information on transits of Jupiter’s central meridian by the Great Red Spot, consult https://www.projectp...eve_grs.htm#apr or page 50 of the April 2019 issue of Sky & Telescope.
Saturn rises at approximately 3:00 a.m. local daylight time as April begins. The Ringed Planet rises by 1:15 a.m. local daylight time, brightens to magnitude +0.5, and subtends 17 arc seconds by the end of the month. At midmonth, its rings span 38 arc seconds and are tilted 24 degrees with respect to the Earth. Saturn is occulted by the Moon from some parts of the world on April 25th. The planet reaches its first stationary point and begins retrograde motion on April 30th. Titan, Saturn’s brightest satellite at eighth magnitude, passes 1.1 arc minute south of the planet on April 2nd and April 18th and 1.1 arc minute north of the planet on April 10th and April 26th. Iapetus is located 1.1 arc minutes south of Saturn and shines at eleventh magnitude on April 7th. By the time this odd moon, which has a dark side and a bright side, reaches greatest elongation nine arc minutes from Saturn on April 28th, it brightens to tenth magnitude. Browse http://www.skyandtel...watching-tools/ for information on Saturn’s satellites.
Uranus is in conjunction with the Sun on April 22nd and consequently is not visible after the first few days of this month.
Eighth-magnitude Neptune is very low in the east at dawn. Venus passes 0.3 degree south of the distant planet on the morning of April 10th. The two planets are only seven degrees in altitude 30 minutes before sunrise. The fourth-magnitude star Phi Aquarii is positioned just five arc minutes south of Neptune on that date.
The dwarf planet Pluto is fairly high in the sky in northwestern Sagittarius during morning twilight.
For more on the planets and how to locate them, browse http://www.nakedeyeplanets.com/
As it heads northwestward through Boötes this month, the main belt asteroid 2 Pallas shines at eighth magnitude. The second asteroid to be discovered reaches opposition for North American observers on the night of April 9th. On April 10th, 2 Pallas passes just two arc minutes east of the third-magnitude star Muphrid (Eta Boötis) and approximately five degrees southwest of the first-magnitude star Arcturus (Alpha Boötis). A finder chart can be found on page 48 of the April 2019 issue of Sky & Telescope. Asteroid 7 Iris is visible as a ninth-magnitude object as it travels northwestward through northeastern Corvus. This main belt asteroid, which is less than half the size of 2 Pallas, reaches opposition on April 5th. A finder chart appears on page 50 of the April 2019 issue of Sky & Telescope. Other asteroids brighter than magnitude +11.0 reaching opposition this month include 405 Thia (magnitude +10.5) on April 20th in Hydra and 44 Nysa (magnitude +9.9) on April 25th in Virgo. Click on http://www.asteroido.../2019_04_si.htm for information on asteroid occultations taking place this month. See https://www.curtrenz.../asteroids.html for additional current information on a number of asteroids.
Comet C/2018 Y1 (Iwamoto), at tenth magnitude and fading fast, is the brightest comet visible this month. It can be found in eastern Perseus. Visit http://cometchasing.skyhound.com/ and http://www.aerith.ne...ly/current.html for information on this month’s comets.
Various events taking place within our solar system are discussed at http://www.bluewater...ed-4/index.html
The fifth-magnitude G-type main-sequence star 61 Virginis - http://www.solstatio...rs/61vir2co.jpg - is a sun-like star at a distance of 28 light years. It hosts three exoplanets and is visible to the naked-eye.
The famous eclipsing variable star Algol (Beta Persei) is at a minimum, decreasing in magnitude from +2.1 to +3.4, on April 2nd, 5th, 8th, 11th, 14th, 16th, 19th, 22nd, 25th, and 28th. A favorable date for observing Algol at mid-eclipse from the eastern United States is on April 10th at 11:49 p.m. EDT or 3:49 UT on April 11th. Consult http://www.skyandtel...watching-tools/ for the times of the eclipses. For more on Algol, see http://stars.astro.i.../sow/Algol.html and http://www.solstatio...rs2/algol3.htm
Data on current supernovae can be found at http://www.rochester...y.org/snimages/
Information pertaining to observing some of the more prominent Messier galaxies can be found at http://www.cloudynig...ur-astronomers/
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, Struve 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)
Notable carbon star for April: V Hydrae (Hydra)
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 3630, NGC 3640, NGC 3646, NGC 3655, NGC 3681, NGC 3684, NGC 3686, NGC 3691, 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)
Top ten binocular deep-sky objects for April: M65, M66, M95, M96, M97, M105, M108, M109, NGC 3115, NGC 3242
Top ten deep-sky objects for April: M65, M66, M95, M96, M97, M105, M108, NGC 3115, NGC 3242, NGC 3628
Challenge deep-sky object for April: Leo I (Leo)
The objects listed above are located between 10:00 and 12:00 hours of right ascension.