All times, unless otherwise noted, are UT (subtract four hours and, when appropriate, one calendar day for EDT)
4/1 The Moon is 0.35 degree north-northwest of the first-magnitude star Aldebaran (Alpha Tauri), with an occultation taking place in Japan, China, Mongolia, India, Saudi Arabia, and northeast Africa, at 9:00; Mercury is at greatest eastern elongation (19.0 degrees) at 10:00
4/2 Mercury is at greatest heliocentric latitude north (7.0 degrees) at 19:00; the Moon is 5.4 degrees south of the bright open cluster M35 in Gemini at 23:00;
4/3 First Quarter Moon occurs at 18:39; 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 begin at 22:21
4/4 The Moon is 9.9 degrees south of the first-magnitude star Pollux (Beta Geminorum) at 12:00
4/5 The Moon is 3.5 degrees south of the bright open cluster M44 (the Beehive Cluster or Praesepe) in Cancer at 12:00
4/6 Saturn is stationary in right ascension at 5:00
4/7 The Moon is 0.7 degree south-southwest of the first-magnitude star Regulus (Alpha Leonis), with an occultation taking place in far southern South America, the Antarctic Peninsula, and southern Polynesia, at 5:00; the Moon is at the ascending node (longitude 152.7 degrees) at 9:16; Jupiter (magnitude -2.5, 44.2" in apparent size) is at opposition at 22:00
4/10 Mercury is stationary in right ascension at 1:00; Jupiter is 2.0 degrees south of the Moon at 21:00
4/11 Full Moon, known as the Egg or Grass Moon, occurs at6:08; the Moon is 6.1 degrees north-northeast of the first-magnitude star Spica (Alpha Virginis) at 10:00
4/13 Venus is stationary in right ascension at 0:00; the periodic comet 41P/Tuttle-Giacobini-Kresák is at perihelion at 23:00
4/14 Uranus is in conjunction with the Sun at 6:00
4/15 The Moon 9.6 degrees north of Antares at 7:00; the equation of time equals zero at 10:00; the Moon is at apogee, subtending29' 28''from a distance of 405,474 kilometers(251,950 miles), at 10:05
4/16 Saturn is 3.2 degrees south of the Moon at 19:00
4/18 Pluto is 2.5 degrees south of the Moon at 14:00; the Sun enters the constellation of Aries at 22:00
4/19 Last Quarter Moon occurs at 9:57
4/20 The Curtiss Cross, an X-shaped clair-obscure illumination effect located between the craters Parry and Gambart, is predicted to begin at 1:27; Mercury is in inferior conjunction with the Sun at 6:00; Pluto is stationary in right ascension at 11:00; the periodic comet 103P/Hartley is at perihelion at 12:00
4/21 Mars is 3.5 degrees south-southeast of the bright open cluster M45 (the Pleiades or Subaru) in Taurus at 20:00; the Moon is at the descending node (longitude 331.5 degrees) at 22:32
4/22 The peak of the Lyrid meteor shower (20 per hour) occurs at 12:00; Neptune is 0.21degrees northwest of the Moon, with an occultation taking place in central Polynesia, southeast Melanesia, New Zealand, and most of Australia, at 20:00
4/23 Venus is 4.9 degrees north-northwest of the Moon at 21:00
4/24 The Moon is 0.8 degree north of asteroid 2 Pallas, with an occultation taking place in Ireland, Iceland, Greenland, and most of North America, at 16:00
4/25 Uranus is 3.5 degrees north-northwest of the moon at 18:00; Mercury is 4.3 degrees north-northeast of the Moon at 20:00; the Moon, Mercury, and Uranus all lie within a circle of diameter 4.3 degrees at 20:00
4/26 Mercury is at the descending node through the ecliptic plane at 5:00; New Moon (lunation 1167) occurs at 12:17
4/27 The Moon is at perigee, subtending33' 15''from a distance of 359,329 kilometers(223,275 miles), at 16:15
4/28 The moon is 9.1 degrees south-southeast of the bright open cluster M45 (the Pleiades or Subaru) in Taurus at 2:00; Comet C/2015 V2 (Johnson) is at opposition at 2:00; Mars is 5.7 degrees north of the moon at 9:00; Mercury (magnitude +3.0) is 0.09 degree southeast of Uranus (magnitude +5.9) at 12:00; the Moon is 0.49 degree north of Aldebaran, with an occultation taking place in northern Africa, Europe, far southern Greenland, eastern Canada, Cuba, and North America, at 18:00
4/30 May Eve, a cross-quarter day; Venus is at greatest illuminated extent at 4:00; the Moon is 5.2 degrees south of the bright open cluster M35 in Gemini at 6:00
Christiaan Huygens (1629-1695) was born this month.
Johann Koehler discovered the elliptical galaxies M50 and M60 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 morning of April 22nd during a waning crescent Moon. 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. For more on this year’s Lyrids, see http://earthsky.org/?p=158735 and http://www.skyandtelescope.com/astronomy-news/meteor-showers-in-2017/
Information on Iridium flares and passes of the ISS, the Tiangong-1, 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 3.9 days old, is illuminated 20.0%, subtends 30.1', and is located in Taurus at 0:00 UT on April 1st. The Moon is at its greatest northern declination of +18.9 degrees on April 3rd and +19.0 degrees on April 30th and its greatest southern declination of -19.0 degrees on April 18th. Longitudinal libration is at a maximum of +5.6 degrees on April 6th and a minimum of -7.4 degrees on April 22nd. Latitudinal librationis at a maximum of +6.7 degrees on April 1st and +6.6 degrees on April 28th and a minimum of -6.7 degrees on April 15th. New Moon occurs on April 26th. Very large tides occur for several days thereafter. The Moon can be seen occulting Aldebaran from various parts of the world twice this month, on April 1st and April 28th. Consult http://www.lunar-occultations.com/iota/bstar/bstar.htm for additional information on these events. Visit http://saberdoesthestars.wordpress.com/2011/07/05/saber-does-the-stars/ for tips on spotting extreme crescent Moons. 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
The Sun is located in Pisces on April 1. It enters Aries on April 18th.
Brightness, apparent size, illumination, distance from the Earth in astronomical units, and location data for the planets and Pluto on April 1: Mercury (-0.2 magnitude, 7.5", 43% illuminated, 0.90 a.u., Pisces),Venus (-4.2, 57.9", 2% illuminated, 0.29 a.u., Pisces),Mars (+1.5 magnitude, 4.2", 96%illuminated, 2.23 a.u., Aries), Jupiter (-2.5 magnitude, 44.2", 100% illuminated, 4.46a.u., Virgo), Saturn (+0.4 magnitude, 17.0", 100% illuminated, 9.77a.u., Sagittarius), Uranus (+5.9 magnitude, 3.4", 100% illuminated, 20.93 a.u. on April 16th, Pisces), Neptune (+7.9 magnitude, 2.2", 100% illuminated, 30.68 a.u. on April 16th, Aquarius), and Pluto (+14.2 magnitude, 0.1", 100% illuminated, 33.16 a.u. on April 16th, Sagittarius).
Mercury and Mars are located in the west and Jupiter in the southeast in the evening. At midnight, Jupiter is in the south. Venus and Neptune can be found in the east, Jupiter in the west, and Saturn in the south in the morning sky.
Mercury, Venus, Uranus, and the Sun are all located in Pisces on April 1st.
Mercury is at greatest eastern elongation on April 1st, reaches its greatest latitude north of the ecliptic plane on April 2nd, and is stationary on April 10th. It is in inferior conjunction on April 20th and is at the descending node through the ecliptic plane on April 26th.
As April progresses, Venus grows increasingly more prominent in the morning sky. On April 13th, it reaches its second stationary point in the Circlet of Pisces and thereafter resumes prograde motion. The Moon passes five degrees north of Venus on April 23rd. Venus decreases in apparent size from 57.9 to 38.5 arc seconds and increases in illumination from 2 to 26% over the course of the month.
Mars sets shortly after 10:00 p.m. local daylight time this month. It shrinks in apparent size to less than four arc seconds. Mars departs Aries and enters Taurus on April 12th. The Red Planet passes less than four degrees south of M45 (the Pleiades) on April 19th and April 20th and lies between the M45 and Melotte 25 (the Hyades) during the final week of April.
Jupiter reaches opposition on April 7th. Jupiter is two degrees south of the Moon on April 10th. Jupiter shrinks in apparent diameter from 44.2 to 43.6 arc seconds and decreases in brightness from magnitude -2.5 to magnitude -2.4 during the course of the month. On April 2nd, Io’s shadow falls on the planet at 11:31 p.m. EDT. Eight minutes later the satellite begins to transit Jupiter’s disk. On April 9th, Io reappears from eclipse by Jupiter’s shadow at 6:18 a.m. EDT. Io begins to transit the planet again at 1:22 a.m. EDT on April 10th, followed by its shadow three minutes later. Europa is occulted by Jupiterat 3:52 a.m. EDT
on April 14th
. Data on other Galilean satellite events is available at http://www.skyandtelescope.com/observing/interactive-sky-watching-tools/
and page 51 of the April issue of Sky & Telescope
. For information on transits of Jupiter’s central meridian by the Great Red Spot, consult and page 50 of the April 2017 issue of Sky & Telescope
As April begins, Saturn rises at approximately 1:30 a.m. local daylight time. The planet rises around 11:30 p.m. local daylight time, brightens to magnitude +0.3, and subtends 17.8 arc seconds by the end of the month. At mid-month, its rings span 39 arc seconds and are tilted more than 26 degrees with respect to the Earth. Saturn is stationary in right ascension on April 6th and commences retrograde (western) motion thereafter. It is situated within four degrees of the open clusters M21 and M23 and the nebulae M 8 (the Lagoon Nebula) and M20 (the Trifid Nebula) for the duration of the month. The waning gibbous Moon passes three degrees north of the Ringed Planet on April 16th. Titan, Saturn’s largest satellite, is north of the planet on April 6th and April 22nd and south of it on April 13th and April 29th. For further information on Saturn’s satellites, browse http://www.skyandtelescope.com/observing/interactive-sky-watching-tools/
Uranus is in conjunction with the Sun on April 14th and consequently is not visible this month.
By the end of April, Neptune lies very low in the east at dawn. Southern hemisphere observers have a more favorable view due to the angle of ecliptic.
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/
Asteroids 16 Psyche and 29 Amphitrite are located in southern Leo just this month. The ninth- and tenth-magnitude asteroids are just northeast of Rho Leonis on April 1st and are less than one half of a degree apart. A 9.5-magnitude star lies between the two asteroids. Psyche heads northwestward and Amphitrite westward and then southeastward through Leo as April unfolds. Asteroids brighter than magnitude +11.0 that reach opposition this month include 105 Artemis (magnitude +10.5) on April 3rd, 416 Vaticana (magnitude +10.9) on April 8th, 63 Ausonia (magnitude +10.1) on April 11th, 230 Athamantis (magnitude +10.6) on April 13th, and 12 Victoria (magnitude +9.8) on April 19th. The thirteenth-magnitude asteroid 599 Luisa occults an 8.5-magnitude star in Scorpius for observers in certain parts of the Eastern Seaboard for as much as 11 seconds on the morning of April 10th. The event is visible along a track extending from Maine to northern Florida. The eleventh-magnitude asteroid 105 Artemis may occult an 8.9-magnitude star in Virgo for as much as 10 seconds on the morning of April 11th from parts of Arizona, Nevada, Utah, Idaho, Montana, and western Canada. Click on http://www.asteroidoccultation.com/2017_04_si.htm for further information on these and other asteroid occultations taking place this month. See http://www.curtrenz.com/asteroids.html for additional current information on asteroids.
Comet 41P/Tuttle-Giacobini-Kresák may reach fifth magnitude this month as it passes through Draco and Hercules. The periodic comet comes closest to the Earth on April 1st and reaches perihelion on April 13th. Visit http://cometchasing.skyhound.com/ and http://www.aerith.net/comet/weekly/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/
A free star map for April can be downloaded at http://www.skymaps.com/downloads.html and http://www.telescope.com/content.jsp?pageName=Monthly-Star-Chart
The fifth-magnitude G-type main-sequence star 61 Virginis - http://www.solstation.com/stars/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 1st, 4th, 7th, 9th, 12th, 15th, 18th, 21st, 24th, 27th, and 29th. Consult http://www.skyandtelescope.com/observing/interactive-sky-watching-tools/ for the times of the eclipses. For more on Algol, see http://stars.astro.illinois.edu/sow/Algol.html and http://www.solstation.com/stars2/algol3.htm
Information pertaining to observing some of the more prominent Messier galaxies can be found at http://www.cloudynights.com/topic/358295-how-to-locate-some-of-the-major-messier-galaxies-and-helpful-advice-for-novice-amateur-astronomers/
Deep-sky object list generators can be found at http://www.virtualcolony.com/sac/ and http://tonightssky.com/MainPage.php
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.