April Celestial Calendar by Dave Mitsky
All times, unless otherwise noted, are UT (subtract four hours and, when appropriate, one calendar day for EDT)
4/2 The Moon is 4.8 degrees north-northeast of the first-magnitude star Antares (Alpha Scorpii) at 00:00; the Moon is at the descending node (longitude 252.6 degrees) at 3:00
4/3 Mercury is at its southernmost latitude from the ecliptic plane (-7.0 degrees) at 8:00
4/4 Last Quarter Moon occurs at 10:03; asteroid 9 Metis (magnitude +9.5) is at opposition in Virgo at 12:00; Pluto is at its northernmost declination (-22.15 degrees) at 15:00
4/6 The Curtiss Cross, an X-shaped clair-obscure illumination effect located between the craters Parry and Gambart, is predicted to be visible at 00:53; the Moon is 3.9 degrees southeast of Saturn at 11:00
4/7 The dwarf planet/asteroid 1 Ceres is in conjunction with the Sun at 7:00; the Moon is 4.2 degrees southeast of Jupiter at 11:00
4/9 The Moon is 4.0 degrees southeast of Neptune at 15:00
4/11 The Moon is 2.7 degrees southeast of Mercury at 10:00
4/12 New Moon (lunation 1216) occurs at 2:31
4/13 Asteroid 3 Juno is stationary at 2:00; the Moon is 2.3 degrees southeast of Uranus at 14:00
4/14 The Moon is at apogee, subtending 29' 25'' from a distance of 406,118 kilometers (252,351 miles), at 17:46
4/15 The Moon is 5.0 degrees southeast of M45 at 9:00; the equation of time is equal to 0 at 9:00
4/16 The Moon is 5.3 degrees north-northwest of the first magnitude star Aldebaran (Alpha Tauri) at 3:00; the Moon is at the ascending node (longitude 71.4 degrees) at 6:00
4/17 The Moon is 0.1 degrees south of Mars, with an occultation taking place in most of the Philippines, Indonesia, southeast Asia, India, the southern portions of the Middle East, and most of central and eastern Africa, at 12:00
4/18 The Moon is 1.0 degrees north-northeast of the bright open cluster M35 in Gemini at 1:00; the Sun enters Aries (longitude 29.1 degrees on the ecliptic) at 23:00
4/19 Mercury is in superior conjunction with the Sun (1.331 astronomical units from the Earth; latitude -2.33 degrees) at 2:00; the Lunar X (the Purbach or Werner Cross), an X-shaped illumination effect involving various rims and ridges between the craters La Caille, Blanchinus, and Purbach, is predicted to be visible at 11:15; the Moon is 6.8 degrees south of the first-magnitude star Castor (Alpha Geminorum) at 14:00; the Moon is 3.2 degrees south of the first-magnitude star Pollux (Beta Geminorum) at 19:00; the longitude of the Sun is 30 degrees at 21:00
4/20 First Quarter Moon occurs at 6:59; the Moon is 3.0 degrees north-northeast of the bright open cluster M44 (the Beehive Cluster or Praesepe) in Cancer at 21:00
4/22 Mercury is at the ascending node through the ecliptic plane at 9:00; the peak of the Lyrid meteor shower (a zenithal hourly rate of 15 to 20 per hour) occurs at 12:00; the Moon is 4.6 degrees north-northeast of the first-magnitude star Regulus (Alpha Leonis) at 14:00; asteroid 4 Vesta is stationary at 18:00; Mars is at its northernmost declination (24.9 degrees) at 22:00
4/23 Venus is 0.2 degrees southeast of Uranus at 2:00
4/24 Mercury is 0.7 degrees north-northwest of Uranus at 7:00; Mercury, Venus, and Uranus lie within a circle with a diameter of 1.7 degrees at 9:00
4/25 Mercury is 1.2 degrees north-northwest of Venus at 18:00
4/26 The Moon is 5.9 degrees north-northeast of Spica at 8:00
4/27 Mars is 0.6 degrees north of the bright open cluster M35 in Gemini at 7:00; the Full Moon, known as the Egg or Grass Moon, occurs at 3:32; the Moon is at perigee, subtending 33' 26'' from a distance of 357,381 kilometers (222,064 miles), at 15:22
4/28 Pluto is stationary, with retrograde motion to begin, at 19:00
4/29 The Moon is 4.7 degrees north-northeast of Antares at 9:00; the Moon is at the descending node (longitude 251.0 degrees) at 9:00
4/30 Uranus is in conjunction with the Sun (20.764 astronomical units from the Earth, latitude -0.43 degrees) at 20:00
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 21st/April 22nd. A typical zenithal hourly rate is about 20 meteors per hour but short outbursts have occurred occasionally. Fireballs are also possible. The radiant lies to the northwest of the first-magnitude star Vega, between the Keystone of Hercules and Lyra. A waxing gibbous Moon will compromise the 2021 Lyrids. It will set about an hour before morning twilight. For more on this year’s Lyrid meteor shower, browse https://earthsky.org...d-meteor-shower and https://www.imo.net/...lyrids-in-2021/
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 18.4 days old, is illuminated 86.9%, subtends 32.8', and is located in Pisces at 0:00 UT on April 1st. The Moon is at its greatest northern declination of +25.5 degrees on April 19th and its greatest southern declination of -25.4 degrees on April 4th. Longitudinal libration is at a maximum of +6.3 degrees on April 6th and a minimum of -7.9 degrees on April 22nd. Latitudinal libration is at a maximum of +6.7 degrees on April 9th and a minimum of -6.7 degrees on April 24th. Favorable librations occur for the following craters: Pingré (April 26th), Bailly (April 27th), and Boguslawski (April 28th). The Curtiss Cross occurs on April 6th and the Lunar X on April 19th. New Moon occurs on April 11th. Large tides will occur following the Full Moon on April 27th. The Moon is at apogee on April 14th (at a distance 63.68 Earth-radii) and at perigee on April 27th (at a distance of 56.03 Earth-radii). The Moon occults Mars on April 17th from certain parts of the world. Browse http://www.lunar-occ...ota/iotandx.htm for information on lunar occultation events. Visit https://saberdoesthe...does-the-stars/ for tips on spotting extreme crescent Moons and https://curtrenz.com/moon.html for Full Moon and other lunar data. Consult http://time.unitariu...moon/where.html for current information on the Moon. Visit http://www.ap-i.net/avl/en/start to download the free Virtual Moon Atlas. Browse https://skyandtelesc...ads/MoonMap.pdf for a lunar map. See https://svs.gsfc.nasa.gov/4768 for a lunar phase and libration calculator and https://quickmap.lro...2vIBvAXwF1SizSg for the Lunar Reconnaissance Orbiter Camera (LROC) Quickmap. Click on https://www.calendar...ndar/2021/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 1st. 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 (-0.5, 5.3", 86% illuminated, 1.26 a.u., Aquarius), Venus (-4.0, 9.7", 100% illuminated, 1.72 a.u., Pisces), Mars (+1.3 magnitude, 5.3", 91% illuminated, 1.76 a.u., Taurus), Jupiter (-2.1 magnitude, 34.7", 99% illuminated, 5.68 a.u., Capricornus), Saturn (+0.8 magnitude, 15.9", 100% illuminated, 10.43 a.u., Capricornus), Uranus (+5.9 magnitude, 3.4", 100% illuminated, 20.73 a.u. on April 16th, Aries), Neptune (+7.9 magnitude, 2.2", 100% illuminated, 30.75 a.u. on April 16th, Aquarius), and Pluto (+14.4 magnitude, 0.1", 100% illuminated, 34.26 a.u. on April 16th, Sagittarius).
Mercury, Venus, Mars, and Uranus are located in the west in the evening. At midnight, Mars can be found in the west. Jupiter and Saturn are in the southeast and Neptune is in the east in the morning sky.
Mercury, Venus, and Uranus lie within a circle with a diameter of 1.7 degrees on April 24th.
Mercury is visible in the morning sky early in the month and returns to the evening sky very late in April. The speediest planet brightens from magnitude -0.5 to magnitude -2.2 and then decreased in brightness to magnitude -1.2 this month. Mercury is at its greatest heliocentric latitude south on April 3rd and achieves superior conjunction on April 19th. It's at the ascending node on April 22nd, is a bit more than one degree north-northwest of Venus on the morning of April 25th, and reaches perihelion on April 27th.
Venus may be visible very low in the west-northwest at evening twilight at the end of the month.
Mars heads eastward through Taurus this month. It passes between Zeta Tauri (Alheka) and Beta Tauri (Elnath), the horns of the Bull, on April 12th and April 13th and enters Gemini on April 24th. Mars forms a near isosceles triangle with the similarly colored first-magnitude stars Betelgeuse and Aldebaran on April 15th. On April 16th, a waxing crescent Moon passes just north of Mars, with an occultation taking place in the Eastern Hemisphere. On April 30th, it forms another almost isosceles triangle with Eta Geminorum (Tejat Posterior) and Mu Geminorum (Propus). Mars passes approximately 0.5 degrees north-northwest of the center of the open cluster M35 on the evening of April 27th. The Red Planet decreases in brightness from magnitude +1.3 to magnitude +1.5 and shrinks in angular size from 5.3 arc seconds to 4.7 arc seconds by the end of April.
Jupiter increases in brightness to magnitude -2.2 and in apparent diameter from 34.7 to 37.3 arc seconds during April. It rises about half an hour after Saturn in the early part of the month. Jupiter occults 44 Capricorni (magnitude +5.9) on the morning of April 2nd. The star's reappearance on the western limb of the planet will be visible from eastern North America. The Galilean satellite Io passes just south of the star at 6:21 a.m. EDT (10:21 UT). A short article on the event can be found on page 49 of the April 2021 issue of Sky & Telescope. A waning crescent Moon passes four degrees south of Jupiter on the morning of April 7th. Jupiter is positioned two degrees north of the third-magnitude star Delta Capricorni (Deneb Algedi) on that date. Jupiter enters Aquarius on April 25th. A shadow transit by Io ends at 6:28 a.m. EDT (10:28 UT) on the morning of April 9th. A list of mutual Galilean satellite events can be found on page 50 of the April 2021 issue of Sky & Telescope. Data on other Galilean satellite events is available at http://www.skyandtel...watching-tools/ and page 51 of the April 2021 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 pages 50 and 51 of the April 2021 issue of Sky & Telescope.
Saturn rises just after 4:00 a.m. local daylight time on April 1st. By the end of the month, it's over 20 degrees in altitude at the beginning of twilight. Saturn lies four degrees north of the waning crescent Moon on April 6th. Titan, Saturn’s brightest satellite, lies 2.6 degrees east of the planet on April 1st. It passes due south of Saturn on April 5th and April 21st and due north of Saturn on April 13th and April 29th. It may be possible to spot Iapetus at greatest western elongation on April 16th when it is positioned eight arc seconds due east of the planet. Browse http://www.skyandtel...watching-tools/ for information on Saturn’s satellites.
Uranus is in conjunction with the Sun on April 30th 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. It's located about five degrees east of the fourth-magnitude star Phi Aquarii.
The dwarf planet Pluto is still not a viable target this month.
For more on the planets and how to locate them, browse http://www.nakedeyeplanets.com/
A summary on the planets for April can be found at https://skynews.ca/a...ts-at-a-glance/
The graphic at https://www.timeandd...lanets/distance displays the apparent and comparative sizes of the planets, along with their magnitudes and distances, for a given date and time.
Asteroid 4 Vesta shines at magnitude +6.6 as it travels northwestward and then southward through Taurus this month. On April 1st, the main belt asteroid is located two degrees east of the fifth-magnitude star 51 Leonis and several degrees southwest of the fourth-magnitude star 60 Leonis. It lies 0.6 degrees southeast of 51 Leonis by the middle of the April and a bit more than one degree southeast of the star as the month ends. Vesta is stationary on April 22nd. Asteroid 9 Metis is at opposition in Virgo on April 4th. Consult https://in-the-sky.o...05_14_100_2.png or page 50 of the April 2021 issue of Sky & Telescope for a finder chart. Asteroid 3 Juno is stationary on April 12th. Click on http://www.asteroido.../2021_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/2020 R4 (ATLAS) shines at approximately eighth-magnitude as it travels rapidly northwestward from Aquila to beyond Boötes during April. It passes very close to the seventh-magnitude open cluster NGC 6709 on April 12th. Visit http://cometchasing.skyhound.com/ and http://www.aerith.ne...t/future-n.html and https://cobs.si/ for additional information on this and other comets visible this month.
A wealth of information on solar system celestial bodies is posted at http://www.curtrenz.com/astronomy.html and http://nineplanets.org/
An informative video discussing astronomical objects worthy of observing each month can be found at https://hubblesite.o...es/tonights-sky
An online interactive star chart appears at https://skyandtelesc...tive-sky-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 2nd, 5th, 8th, 11th, 14th, 17th, 19th, 22nd, 25th, and 28th. Consult http://www.skyandtel...watching-tools/ and page 49 of the April 2021 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/
Information on observing some of the more prominent Messier galaxies is available at http://www.cloudynig...ur-astronomers/
Telrad finder charts for the SAC’s 110 Best of the NGC are available at http://sao64.free.fr...ataloguesac.pdf
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.