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 First Quarter Moon occurs at 10:21
4/2 The Moon is 8.5 degrees south of the first-magnitude star Castor (Alpha Geminorum) at 4:00; the Moon is 4.9 degrees south of the first-magnitude star Pollux (Beta Geminorum) at 8:00; asteroid 3 Juno (magnitude +9.7) is at opposition at 20:00
4/3 The Moon is 1.3 degrees north of the bright open cluster M44 (the Beehive Cluster or Praesepe) in Cancer at 7:00; Mercury is 1.4 degrees south of Neptune at 15:00; Venus is 0.3 degree south of the bright open cluster M45 (the Pleiades or Subaru) in Taurus at 20:00
4/4 Mercury (magnitude 0.0) is 1.3 degrees south-southeast of Neptune (magnitude +8.0) at 1:00; Venus (magnitude -4.4) passes 16 arc minutes southeast of Alcyone (magnitude +2.9) at 2:00; the Moon is 3.8 degrees north-northeast of the first-magnitude star Regulus (Alpha Leonis) at 22:00
4/7 The Moon is at its closest perigee of 2020, subtending 33' 29'' from a distance of 356,907 kilometers (221,771 miles), at 18:09
4/8 The Martian northern hemisphere autumnal equinox occurs at 1:00; the Full Moon, known as the Egg or Grass Moon, occurs at 2:35; the Moon is 6.7 degrees northeast of the first magnitude star Spica (Alpha Virginis) at 12:00
4/10 Venus is at its northernmost latitude from the ecliptic plane (3.4 degrees) at 18:00
4/11 The Moon is 6.4 degrees northeast of the first magnitude star Antares (Alpha Scorpii) at 15:00
4/13 The Moon is at the descending node (longitude 271.6 degrees) at 3:00
4/14 The Moon is 1.2 degrees south of the dwarf planet Pluto, with an occultation taking place in a portion of the Antarctic peninsula, at 22:00; Last Quarter Moon occurs at 22:56; the Moon is 2 degrees south of Jupiter at 23:00
4/15 Venus is 9.9 degrees north-northwest of the first magnitude star Aldebaran (Alpha Tauri) at 2:00; the equation of time is equal to 0 at 3:00; the Moon, Jupiter, and Saturn lie within a circle with a diameter of 5.5 degrees at 7:00; the Moon is 2.4 degrees southeast of Saturn at 11:00; Jupiter is at western quadrature (90 degrees from the Sun) at 11:00
4/16 Mercury is at its southernmost latitude from the ecliptic plane (-7.0 degrees) at 11:00; the Moon is 2.0 degrees south of Mars at 5:00; the Curtiss Cross, an X-shaped clair-obscure illumination effect located between the craters Parry and Gambart, is predicted to be visible at 15:59
4/18 The Sun enters Aries (longitude 29.1 degrees on the ecliptic) at 17:00
4/19 The Moon is 3.9 degrees southeast of Neptune at 11:00; the Sun’s longitude is 30 degrees at 15:00
4/20 The Moon is at apogee, subtending 29' 24'' from a distance of 406,462 kilometers (252,564 miles), at 19:00
4/21 Saturn is at western quadrature (90 degrees from the Sun) at 7:00; the Moon is 3 degrees south of Mercury at 17:00
4/22 The peak of the Lyrid meteor shower (a zenithal hourly rate of 15 to 20 per hour) occurs at 6:00
4/23 New Moon (lunation 1204) occurs at 2:26; the Moon is 3.7 degrees southeast of Uranus at 10:00
4/24 The apparent brightness of Mars exceeds magnitude +0.5 today
4/25 Pluto is stationary in longitude, with retrograde (westward) motion to commence, at 5:00; the Moon is 6.6 degrees southeast of M45 at 10:00
4/26 Pluto is stationary in right ascension, with retrograde motion to begin, at 1:00; the Moon is 3.7 degrees north of Aldebaran at 3:00; Uranus is in conjunction with the Sun (20.811 astronomical units from the Earth, latitude -0.47 degree) at 9:00; the Moon is 0.1 degree north of asteroid 4 Vesta, with an occultation taking place in southern Japan, the Philippines, most of southeastern Asia, China, northern and central India, southern Kazakhstan, most of the Middle East, and central and northeastern Africa, at 11:00; the Moon is 5.9 degrees southeast of Venus at 18:00; the Moon is at the ascending node (longitude 90.3 degrees) at 18:00
4/27 The Moon is 0.8 degree southeast of the bright open cluster M35 in Gemini at 23:00; Venus is at greatest brilliancy (magnitude -4.7) at 18:00
4/29 The Moon is 8.3 degrees south of Castor at 10:00; the Moon is 4.6 degrees south of Pollux at 15:00
4/30 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 2:04; the Moon is 1.6 degrees north of M44 at 14:00; First Quarter Moon occurs at 20:38
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. A typical zenithal hourly rate is about 20 meteors per hour but short outbursts have occurred occasionally. Fireballs are also possible. The radiant lies between the Keystone of Hercules and Lyra. Moonlight will not compromise the 2020 Lyrids. For more on this year’s Lyrids, see the article on page 49 of the April 2020 issue of Sky & Telescope or browse https://earthsky.org...er-guide#lyrids and https://www.amsmeteo...hower-calendar/
Information on passes of the ISS, the USAF’s X-37B, the HST, Starlink, and other satellites can be found at http://www.heavens-above.com/
The Moon is 7.4 days old, is illuminated 43.8%, subtends 31.2', and is located in Gemini at 0:00 UT on April 1st. The Moon is at its greatest northern declination of +23.6 degrees on April 1st and +23.9 degrees on April 29 and its greatest southern declination of -23.8 degrees on April 14th. Longitudinal libration is at a maximum of +7.5 degrees on April 14th and a minimum of -8.0 degrees on April 2nd and -7.2 on April 30th. Latitudinal libration is at a maximum of +6.6 degrees on April 20th and a minimum of -6.5 degrees on April 7th. The Moon is at perigee on April 7th (at a distance of 55.96 Earth-radii) and at apogee on April 20th (at a distance 63.73 Earth-radii). The Moon will be at its closest to the Earth for the year on April 7th. Large tides will occur following the Full Moon on April 8th. New Moon occurs on April 22nd. The Last Quarter Moon, Jupiter, Saturn, and Mars form a 20-degree arc above the south-southeastern horizon on the morning of April 14th. The waning crescent Moon is positioned three degrees south of Saturn, with Jupiter to the upper right and Mars to the left, on the morning of April 15th. On April 26th, the waxing crescent Moon is positioned about four degrees from the third-magnitude star Zeta Tauri. The Moon occults Pluto on April 14th and asteroid 4 Vesta on April 26th from certain parts of the world. Consult http://www.lunar-occ...ota/iotandx.htm for information on occultation events. Visit https://saberdoesthe...does-the-stars/ for tips on spotting extreme crescent Moons and http://www.curtrenz.com/moon06.html for Full Moon data. Consult http://time.unitariu...moon/where.html or download http://www.ap-i.net/avl/en/start for current information on the Moon. See https://svs.gsfc.nasa.gov/4768 for a lunar phase and libration calculator and https://svs.gsfc.nasa.gov/4768 for the Lunar Reconnaissance Orbiter Camera (LROC) Quickmap. Click on https://www.calendar...ndar/2020/april for a lunar phase calendar for this month. Times and dates for the lunar crater 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 (0.0, 6.6", 64% illuminated, 1.02 a.u., Aquarius), Venus (-4.5, 25.5", 47% illuminated, 0.65 a.u., Taurus), Mars (+0.8 magnitude, 6.4", 88% illuminated, 1.46 a.u., Capricornus), Jupiter (-2.1 magnitude, 37.0", 99% illuminated, 5.32 a.u., Sagittarius), Saturn (+0.7 magnitude, 16.1", 100% illuminated, 10.30 a.u., Sagittarius), Uranus (+5.9 magnitude, 3.4", 100% illuminated, 20.79 a.u. on April 16th, Aries), Neptune (+7.9 magnitude, 2.2", 100% illuminated, 30.73 a.u. on April 16th, Aquarius), and Pluto (+14.3 magnitude, 0.1", 100% illuminated, 33.98 a.u. on April 16th, Sagittarius).
Venus and Uranus are located in the west in the evening. Mercury and Neptune can be found in the east, and Mars, Jupiter, and Saturn in the southeast in the morning sky.
Mercury brightens from magnitude 0.0 to magnitude -1.2 this month as it decreases in angular (apparent) size from 6.6 arc seconds to 5.1 arc seconds but increases in illumination from 64% to 98%. Mercury has a close conjunction with Neptune on April 3rd. The speediest planet shines at magnitude -0.2 by April 10th and is at its greatest heliocentric latitude south on April 16th. The Moon passes three degrees south of Mercury on April 16th. Observers in the southern hemisphere are favored during the current morning apparition of Mercury.
Brilliant Venus is in one of the very best months of its eight-year cycle of recurring apparitions. During April, Venus grows in brightness to magnitude -4.7 and in angular size to 38.2 arc seconds but drops in illumination from 47% to 26%. On the first day of April, the brightest planet sets approximately four hours after the Sun. On April 3rd, Venus passes one quarter degree southeast of the third-magnitude star Alcyone (Eta Tauri), the brightest star in M45 (the Pleiades). On that day eight years later, Venus will come exceptionally close to the fourth-magnitude star Merope (23 Tauri). The waning gibbous Moon passes six degrees to the south of Venus on April 26th. Venus reaches its greatest illuminated extent, which is the optimum combination of angular size and phase angle, on the evening of April 27th.
Mars increases in brightness from magnitude +0.8 to magnitude +0.4 and grows in angular size from 6.4 arc seconds to 7.6 arc seconds by the end of April. The Red Planet is one degree southeast of Saturn on the morning of April 1st. On April 16th, a waning crescent Moon lies two degrees south of Mars. By the end of the month, Mars is 2.7 degrees due west of the third-magnitude star Deneb Algedi (Delta Capricorni) and rises about three hours before the Sun.
Jupiter increases in brightness to magnitude -2.3 and in apparent diameter from 37.0 to 40.6 arc seconds during April. A very faint Pluto is 45 arc minutes south of Jupiter on April 6th. As the month begins, Jupiter rises just before 1:30 a.m. local daylight time. A waning gibbous Moon passes within two degrees of Jupiter on the morning of April 23rd. The Galilean satellite Ganymede undergoes a shadow transit that ends at 5:52 a.m. EDT (9:52 UT) on April 15th, Europa transits Jupiter starting at 5:17 a.m. EDT (9:17 UT) on April 19th, Io’s shadow crosses Jupiter beginning at 4:43 a.m. EDT (8:43 UT) on April 20th, and Ganymede reappears from occultation shortly after the shadow of Europa begins to transit the planet at 5:18 a.m. EDT (9:18 UT) on April 26th. Data on other Galilean satellite events is available at http://www.skyandtel...watching-tools/ and page 51 of the April 2020 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 2020 issue of Sky & Telescope.
Saturn rises with Mars at approximately 4:00 a.m. local daylight time on April 1st. As April progresses, Jupiter moves closer to Saturn from the west while Mars heads away from Saturn to the east. The three planets are equally spaced, with Saturn approximately 5.5 degrees from Jupiter and Mars, on April 9th. The Ringed Planet rises before 2:00 a.m. local daylight time, brightens to magnitude +0.6, and subtends 16.9 arc seconds by the end of the month. At midmonth, its rings span 37 arc seconds and are inclined by about 21 degrees. Saturn is two degrees north of the Last Quarter Moon on April 15th. Saturn is at western quadrature on April 21st. Titan, Saturn’s brightest satellite at eighth magnitude, will most likely be the only Saturnian satellite visible in early April due to Saturn’s meager altitude, only some 15 degrees, at the start of morning twilight. Browse http://www.skyandtel...watching-tools/ for information on Saturn’s satellites.
Uranus is in conjunction with the Sun on April 26th and consequently is not visible after the first few days of this month.
Eighth-magnitude Neptune is very low in the east at dawn in late April.
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/
Asteroid 4 Vesta shines at magnitude +8.5 as it travels northeastward through Taurus this month. On April 7th, the main belt asteroid passes 3.7 degrees north of the fourth-magnitude star Prima Hyadum (Gamma Tauri) in Melotte 25 (the Hyades); on April 12th, it passes 30 arc minutes north of the fourth-magnitude star Ain (Epsilon Tauri), another member of the Hyades. Four days later it lies several degrees north of the first-magnitude star Aldebaran (Alpha Tauri). Vesta passes somewhat less than two degrees north of the open cluster NGC 1647 on April 23rd. Asteroid 3 Juno (magnitude +9.5) is at opposition in Virgo on April 2nd. It passes one half degree south of the third-magnitude star Minelauva (Delta Virginis) on the nights of April 9th and 10th. A finder chart can be found on page 50 of the April 2020 issue of Sky & Telescope. Asteroids brighter than magnitude +11.0 reaching opposition this month include 6 Hebe (magnitude +10.1) on April 4th, 40 Harmonia (magnitude +9.8) on April 23rd, and 23 Thalia (magnitude +10.0) on April 24th. Click on http://www.asteroido.../2020_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/2019 Y4 (ATLAS) is the brightest comet visible this month. It can be found in Camelopardalis. See http://www.cometwatc...eye-brightness/ and https://skyandtelesc...ked-eye-object/ for more on this comet, which could brighten to naked-eye visibility by May. Comet C/2017 T2 (PanSTARRS) travels northeastward through Camelopardalis. The eighth-magnitude comet passes several degrees north of the spiral galaxy IC 342 on April 9th. Visit http://cometchasing.skyhound.com/ and http://www.aerith.ne...ly/current.html for information on this month’s comets.
A wealth of current information on solar system celestial bodies is posted at http://www.curtrenz.com/astronomy.html and http://nineplanets.org/
Information on the celestial events transpiring each week can be found at http://astronomy.com/skythisweek and http://www.skyandtel...ky-at-a-glance/
Free star maps for April can be downloaded at http://www.skymaps.com/downloads.html and https://www.telescop...thly-Star-Chart
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 3rd, 6th, 9th, 12th, 15th, 17th, 20th, 23rd, 26th, and 29th. Favorable dates for observing Algol at mid-eclipse from the eastern United States occur on April 12th at 12:14 a.m. EDT (4:14 UT) and April 14th at 9:03 p.m. EDT (1:03 UT on April 15th). Consult http://www.skyandtel...watching-tools/ and page 49 of the April 2020 issue of Sky & Telescope for the times of the eclipses. For more on Algol, see http://stars.astro.i.../sow/Algol.html and http://www.solstatio...ars2/algol3.htm
Data on current supernovae can be found at http://www.rochester...y.org/snimages/
Finder charts for the Messier objects and other deep-sky objects are posted at https://freestarcharts.com/messier and https://freestarcharts.com/ngc-ic and http://www.cambridge..._april-june.htm
Telrad finder charts for the Messier Catalog and the SAC’s 110 Best of the NGC are posted at http://www.astro-tom...charts/map1.pdf and http://www.saguaroas...o110BestNGC.pdf respectively.
Information pertaining to observing some of the more prominent Messier galaxies can be found at http://www.cloudynig...ur-astronomers/
Stellarium and Cartes du Ciel are two excellent freeware planetarium programs that are available at http://stellarium.org/ and https://www.ap-i.net/skychart/en/start
Deep-sky object list generators can be found at http://www.virtualcolony.com/sac/ and http://tonightssky.com/MainPage.php
Freeware sky atlases can be downloaded at http://www.deepskywa...-atlas-full.pdf and http://astro.mxd120....ee-star-atlases
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 deep-sky objects for April: M65, M66, M95, M96, M97, M105, M108, NGC 3115, NGC 3242, NGC 3628
Top ten binocular deep-sky objects for April: M65, M66, M95, M96, M97, M105, M108, M109, NGC 3115, NGC 3242
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.