Post by Dave Mitsky on Apr 1, 2016 7:07:29 GMT
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 Mercury is at the ascending node at 1:00; Pluto is 3.3 degrees south of the Moon at 3:00; the Curtiss Cross, an X-shaped clair-obscure illumination effect located between the craters Parry and Gambart, is predicted to begin at 4:20; a double Galilean satellite shadow transit begins at 20:18
4/2 Asteroid 18 Melpomene is 1.1 degrees north-northwest of the Moon at 2:00
4/3 A double Galilean satellite shadow transit begins at 15:11
4/5 Neptune is 1.8 degrees south-southeast of the Moon at 0:00; a double Galilean satellite shadow transit begins at 9:37; Mercury is at perihelion at 17:00; the Moon is at the descending node at 17:26
4/6 Venus is 0.66 degree south-southeast of the Moon, with an occultation occurring in northwestern Asia, the northern Middle East, Europe, and northern Africa at 8:00
4/7 New Moon (lunation 1154) occurs at 11:24; Uranus is 1.9 degrees north-northwest of the Moon at 15:00; the Moon is at perigee, subtending 33' 28'' from a distance of 357,163 kilometers (221,931 miles), at 18:00
4/8 A double Galilean satellite shadow transit begins at 22:55
4/9 Asteroid 4 Vesta is 0.02 degree south of the Moon, with an occultation occurring in Hawaii, Micronesia, most of the Philippine Islands, northwestern Australia, Malaysia, and Indonesia at 4:00; Uranus is in conjunction with the Sun at 21:00
4/10 The Moon is 0.3 degree north of the first-magnitude star Aldebaran (Alpha Tauri), with an occultation occurring in the Azores, the northern Caribbean, southern Canada, the contiguous United States, northern Mexico, and Hawaii, at 22:00
4/11 Venus is at its greatest heliocentric latitude south at 18:00
4/12 The Moon is 6.0 degrees south of the bright open cluster M35 in Gemini at 12:00; the periodic comet 9P/Tempel 1 is closest to the Earth at 23:00
4/14 First Quarter Moon occurs at 3:59; 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 13:39
4/15 The equation of time equals zero at 4:00; the Moon is 4.9 degrees south of the bright open cluster M44 (the Beehive Cluster or Praesepe) in Cancer at 5:00; Mercury is at its greatest heliocentric latitude north at 22:00
4/17 The Moon is 2.4 degrees south-southwest of the first-magnitude star Regulus (Alpha Leonis) at 0:00; Mars is stationary in right ascension at 2:00
4/18 Jupiter is 2.1 degrees north-northeast of the Moon at 3:00; Pluto is stationary in right ascension at 4:00; Mercury is at greatest eastern elongation (19.9 degrees) at 14:00; the Sun enters the constellation of Aries at 16:00; the Moon is at the ascending node at 18:05
4/20 Mars (magnitude -1.1) is 7.2 degrees west of Saturn (magnitude +0.3) at 4:00
4/21 The Moon is 4.8 degrees north-northeast of the first-magnitude star Spica (Alpha Virginis) at 12:00; the Moon is at apogee, subtending 29' 25'' from a distance of 406,351 kilometers (252,495 miles), at 16:00
4/22 Full Moon, known as the Egg or Grass Moon, occurs at 5:24; the peak of the Lyrid meteor shower (20 per hour) occurs at 6:00; Venus (magnitude -3.9) is 0.81 degree south-southeast of Uranus (magnitude +5.9) at 21:00
4/25 Mars is 4.9 degrees south of the Moon at 6:00; the Moon is 9.6 degrees north of the first-magnitude star Antares (Alpha Scorpii) at 8:00; Saturn is 3.3 degrees south of the Moon at 20:00
4/26 Mars is 4.9 degrees north of the first-magnitude star Antares (Alpha Scorpii) at 21:00
4/27 Asteroid 3 Juno (magnitude +10.0) is at opposition at 3:00
4/28 Mercury is 6.8 degrees west-southwest of the bright open cluster M45 (the Pleiades) in Taurus at 9:00; Pluto is 3.1 degrees south of the moon at 10:00; Mars is at the descending node at 20:00
4/29 Mercury is stationary in right ascension at 4:00
4/30 Last Quarter Moon occurs at 3:29; the Curtiss Cross is predicted to begin at 16:39
Christiaan Huygens (1629-1695) was born this month.
The first photograph of the Sun was taken on April 2, 1845. 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 but is severely compromised by a Full 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 earthsky.org/?p=158735 and www.skyandtelescope.com/astronomy-news/observing-news/meteor-showers-in-2016/
Information on Iridium flares and passes of the ISS, the Tiangong-1, the USAF’s X-37B, the HST, and other satellites can be found at www.heavens-above.com/
The Moon is 22.9 days old, is illuminated 46.5%, subtends 30.4', and is located in Sagittarius at 0:00 UT on April 1st. It’s at its greatest northern declination of +18.2 degrees on April 13th and its greatest southern declination of -18.4 degrees on April 27th. Latitudinal libration is at a maximum of +6.7 degrees on April 12th and a minimum of -6.7 degrees on April 26th. Longitudinal libration is at a maximum of +7.6 degrees on April 14th and -7.7 degrees on April 2nd and -7.4 degrees on April 30th. New Moon occurs on April 7th. Very large tides occur from April 8th through April 11th. The 17%-illuminated Moon occults Aldebaran on the afternoon of April 10th. Two apparitions of the Curtiss Cross take place this month. Visit 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 www.lunar-occultations.com/rlo/rays/rays.htm
The Sun is located in Pisces on April 1.
Brightness, apparent size, illumination, distance from the Earth in astronomical units, and location data for the planets and Pluto on April 1: Mercury (-1.5 magnitude, 5.3", 94% illuminated, 1.27 a.u., Pisces), Venus (-3.8, 10.3", 96% illuminated, 1.62 a.u., Aquarius), Mars (-0.5 magnitude, 11.8", 93% illuminated, 0.79 a.u., Scorpius), Jupiter (-2.4 magnitude, 43.6", 100% illuminated, 4.52 a.u., Leo), Saturn (+0.3 magnitude, 17.4", 100% illuminated, 9.55 a.u., Ophiuchus), Uranus (+5.9 magnitude, 3.4", 100% illuminated, 20.96 a.u. on April 16th, Pisces), Neptune (+7.9 magnitude, 2.2", 100% illuminated, 30.66 a.u. on April 16th, Aquarius), and Pluto (+14.2 magnitude, 0.1", 100% illuminated, 32.91 a.u. on April 16th, Sagittarius).
Mercury is located in the west and Jupiter in the southeast in the evening. At midnight, Mars is in the southeast, Jupiter is in the southwest, and Saturn is in the southeast. Venus can be found in the east, Mars in the southwest, Saturn in the south, and Neptune in the east in the morning sky.
At midmonth, Mercury can be seen during morning twilight, Venus rises at 6:00 a.m., Mars rises at 11:00 p.m. and transits the meridian at 4:00 a.m., Jupiter transits the meridian at 10:00 p.m. and sets at 5:00 a.m., and Saturn rises at midnight and transits the meridian at 4:00 a.m. local daylight time for observers at latitude 40 degrees north.
Mars, Saturn, the waning gibbous Moon, and Antares are in quasi-conjunction on the morning of April 25th. The four celestial objects fit within a circle ten degrees in diameter. The Moon lies north of Mars and Saturn and Antares is south of the two planets and the Moon.
Mercury is at perihelion on April 5th. A waxing crescent Moon passes within eight degrees of the planet on April 8th. Mercury reaches greatest eastern elongation on April 18th, when it will shine at magnitude 0 and attain a sunset altitude of 19 degrees at latitude 40 degrees north. Mercury is illuminated approximately 38% and subtends approximately 7.5 arc seconds on that date. It is still 10 degrees above the west-northwestern horizon 45 minutes after sunset. Due to the tilt of tilt of the ecliptic in the spring, this will be the finest apparition of the planet of 2016 for those living in mid-northern latitudes.
Venus heads sunward as the month progresses. It rises less than 30 minutes before the Sun in early April. The brightest planet is occulted by the Moon on April 6th. Venus decreases slightly in apparent size from 10.3 to 9.8 arc seconds, while remaining fairly constant in illumination and brightness, over the course of the month.
Mars brightens from magnitude -0.5 to magnitude -1.4 and grows in apparent size from 11.8 arc seconds to 16.0 arc seconds, the biggest it has appeared in a decade, this month. It exits Scorpius and enters Ophiuchus on April 3rd. On April 16th, the apparent brightness of Mars exceeds magnitude -1.0. The next day, April 17th, the Red Planet is stationary and starts its retrograde opposition loop, as the Earth passes between Mars and the Sun. Saturn and Mars will be seven degrees apart on that date. Mars is greater than 15 arc seconds in apparent diameter on April 23rd. On April 28th, the Red Planet passes the descending node and is south of the ecliptic. The waning gibbous Moon passes five degrees north of Mars on the morning of April 25th. Mars departs Ophiuchus and reenters Scorpius on April 30th. An article on observing the Mars during its 2016 apparition can be found on pages 48-50 of the April issue of Sky & Telescope.
Jupiter retrogrades through Leo this month. It passes two degrees north of the Moon on April 18th. Jupiter shrinks in apparent diameter from 43.6 to 40.9 arc seconds and decreases in brightness from magnitude -2.4 to magnitude -2.3 during the course of the month. The gas giant passes seven arc minutes north of the fifth-magnitude star Chi Leonis, which may be mistaken for a Galilean satellite, on April 8th. A number of Galilean satellite events take place on the night of April 6th/7th. Io begins a transit of Jupiter at 9:52 p.m. EDT on April 6th. Io’s shadow falls on the planet at 10:32 p.m. EDT. At 10:48 p.m. EDT, Europa is occulted by Jupiter. A transit by Ganymede commences at 1:01 a.m. EDT on April 7th. Europa reappears from eclipse by Jupiter’s shadow at 2:54 a.m. EDT. A shadow transit by Ganymede commences at 3:45 a.m. EDT. Data on other Galilean satellite events is available at 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 51 of the April issue of Sky & Telescope.
Saturn brightens to magnitude +0.2 this month. Its rings span 40 arc seconds and are tilted 26 degrees with respect to the Earth. The waning gibbous Moon passes three degrees north of the Ringed Planet on April 25th. Titan, Saturn’s largest satellite, is due north of the planet on April 3rd and April 19th and due south of it on April 11th and April 27th. Iapetus shines at tenth magnitude and lies nine arc minutes from the planet at greatest western elongation on April 5th. By April 25th, the peculiar satellite has dimmed to eleventh magnitude as it passes two arc minutes north of Saturn. For further information on Saturn’s satellites, browse www.skyandtelescope.com/observing/interactive-sky-watching-tools/
Uranus is in conjunction with the Sun on April 9th and consequently is not observable from the northern hemisphere this month.
Neptune lies 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 www.nakedeyeplanets.com/
Asteroid 6 Hebe glides northwestward through the constellation of Leo this month. The tenth magnitude asteroid passes less than three degrees north of the second-magnitude star Denebola (Beta Leonis). On April 27th, asteroid 3 Juno (magnitude +10.0) reaches opposition in Virgo. The faint asteroid 216 Kleopatra (magnitude +12.7) occults a 10.9-magnitude star in Libra for as much as12 seconds on the morning of April 5th. The event is visible along a track extending from Florida to North Dakota. Click on asteroidoccultation.com/2016_04_si.htm respectively for further information on this and other asteroid occultations taking place this month. See www.curtrenz.com/asteroids.html for additional current information on asteroids.
Visit cometchasing.skyhound.com/ and 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 www.curtrenz.com/astronomical and nineplanets.org/
A free star map for April can be downloaded at www.skymaps.com/downloads.html and www.telescope.com/content.jsp?pageName=Monthly-Star-Chart
The fifth-magnitude G-type main-sequence star 61 Virginis - 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 2nd, 5th, 7th, 10th, 13th, 16th, 19th, 22nd, 25th, 27th, and 30th. For more on Algol, see stars.astro.illinois.edu/sow/Algol.html and www.solstation.com/stars2/algol3.htm
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.
All times, unless otherwise noted, are UT (subtract four hours and, when appropriate, one calendar day for EDT)
4/1 Mercury is at the ascending node at 1:00; Pluto is 3.3 degrees south of the Moon at 3:00; the Curtiss Cross, an X-shaped clair-obscure illumination effect located between the craters Parry and Gambart, is predicted to begin at 4:20; a double Galilean satellite shadow transit begins at 20:18
4/2 Asteroid 18 Melpomene is 1.1 degrees north-northwest of the Moon at 2:00
4/3 A double Galilean satellite shadow transit begins at 15:11
4/5 Neptune is 1.8 degrees south-southeast of the Moon at 0:00; a double Galilean satellite shadow transit begins at 9:37; Mercury is at perihelion at 17:00; the Moon is at the descending node at 17:26
4/6 Venus is 0.66 degree south-southeast of the Moon, with an occultation occurring in northwestern Asia, the northern Middle East, Europe, and northern Africa at 8:00
4/7 New Moon (lunation 1154) occurs at 11:24; Uranus is 1.9 degrees north-northwest of the Moon at 15:00; the Moon is at perigee, subtending 33' 28'' from a distance of 357,163 kilometers (221,931 miles), at 18:00
4/8 A double Galilean satellite shadow transit begins at 22:55
4/9 Asteroid 4 Vesta is 0.02 degree south of the Moon, with an occultation occurring in Hawaii, Micronesia, most of the Philippine Islands, northwestern Australia, Malaysia, and Indonesia at 4:00; Uranus is in conjunction with the Sun at 21:00
4/10 The Moon is 0.3 degree north of the first-magnitude star Aldebaran (Alpha Tauri), with an occultation occurring in the Azores, the northern Caribbean, southern Canada, the contiguous United States, northern Mexico, and Hawaii, at 22:00
4/11 Venus is at its greatest heliocentric latitude south at 18:00
4/12 The Moon is 6.0 degrees south of the bright open cluster M35 in Gemini at 12:00; the periodic comet 9P/Tempel 1 is closest to the Earth at 23:00
4/14 First Quarter Moon occurs at 3:59; 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 13:39
4/15 The equation of time equals zero at 4:00; the Moon is 4.9 degrees south of the bright open cluster M44 (the Beehive Cluster or Praesepe) in Cancer at 5:00; Mercury is at its greatest heliocentric latitude north at 22:00
4/17 The Moon is 2.4 degrees south-southwest of the first-magnitude star Regulus (Alpha Leonis) at 0:00; Mars is stationary in right ascension at 2:00
4/18 Jupiter is 2.1 degrees north-northeast of the Moon at 3:00; Pluto is stationary in right ascension at 4:00; Mercury is at greatest eastern elongation (19.9 degrees) at 14:00; the Sun enters the constellation of Aries at 16:00; the Moon is at the ascending node at 18:05
4/20 Mars (magnitude -1.1) is 7.2 degrees west of Saturn (magnitude +0.3) at 4:00
4/21 The Moon is 4.8 degrees north-northeast of the first-magnitude star Spica (Alpha Virginis) at 12:00; the Moon is at apogee, subtending 29' 25'' from a distance of 406,351 kilometers (252,495 miles), at 16:00
4/22 Full Moon, known as the Egg or Grass Moon, occurs at 5:24; the peak of the Lyrid meteor shower (20 per hour) occurs at 6:00; Venus (magnitude -3.9) is 0.81 degree south-southeast of Uranus (magnitude +5.9) at 21:00
4/25 Mars is 4.9 degrees south of the Moon at 6:00; the Moon is 9.6 degrees north of the first-magnitude star Antares (Alpha Scorpii) at 8:00; Saturn is 3.3 degrees south of the Moon at 20:00
4/26 Mars is 4.9 degrees north of the first-magnitude star Antares (Alpha Scorpii) at 21:00
4/27 Asteroid 3 Juno (magnitude +10.0) is at opposition at 3:00
4/28 Mercury is 6.8 degrees west-southwest of the bright open cluster M45 (the Pleiades) in Taurus at 9:00; Pluto is 3.1 degrees south of the moon at 10:00; Mars is at the descending node at 20:00
4/29 Mercury is stationary in right ascension at 4:00
4/30 Last Quarter Moon occurs at 3:29; the Curtiss Cross is predicted to begin at 16:39
Christiaan Huygens (1629-1695) was born this month.
The first photograph of the Sun was taken on April 2, 1845. 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 but is severely compromised by a Full 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 earthsky.org/?p=158735 and www.skyandtelescope.com/astronomy-news/observing-news/meteor-showers-in-2016/
Information on Iridium flares and passes of the ISS, the Tiangong-1, the USAF’s X-37B, the HST, and other satellites can be found at www.heavens-above.com/
The Moon is 22.9 days old, is illuminated 46.5%, subtends 30.4', and is located in Sagittarius at 0:00 UT on April 1st. It’s at its greatest northern declination of +18.2 degrees on April 13th and its greatest southern declination of -18.4 degrees on April 27th. Latitudinal libration is at a maximum of +6.7 degrees on April 12th and a minimum of -6.7 degrees on April 26th. Longitudinal libration is at a maximum of +7.6 degrees on April 14th and -7.7 degrees on April 2nd and -7.4 degrees on April 30th. New Moon occurs on April 7th. Very large tides occur from April 8th through April 11th. The 17%-illuminated Moon occults Aldebaran on the afternoon of April 10th. Two apparitions of the Curtiss Cross take place this month. Visit 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 www.lunar-occultations.com/rlo/rays/rays.htm
The Sun is located in Pisces on April 1.
Brightness, apparent size, illumination, distance from the Earth in astronomical units, and location data for the planets and Pluto on April 1: Mercury (-1.5 magnitude, 5.3", 94% illuminated, 1.27 a.u., Pisces), Venus (-3.8, 10.3", 96% illuminated, 1.62 a.u., Aquarius), Mars (-0.5 magnitude, 11.8", 93% illuminated, 0.79 a.u., Scorpius), Jupiter (-2.4 magnitude, 43.6", 100% illuminated, 4.52 a.u., Leo), Saturn (+0.3 magnitude, 17.4", 100% illuminated, 9.55 a.u., Ophiuchus), Uranus (+5.9 magnitude, 3.4", 100% illuminated, 20.96 a.u. on April 16th, Pisces), Neptune (+7.9 magnitude, 2.2", 100% illuminated, 30.66 a.u. on April 16th, Aquarius), and Pluto (+14.2 magnitude, 0.1", 100% illuminated, 32.91 a.u. on April 16th, Sagittarius).
Mercury is located in the west and Jupiter in the southeast in the evening. At midnight, Mars is in the southeast, Jupiter is in the southwest, and Saturn is in the southeast. Venus can be found in the east, Mars in the southwest, Saturn in the south, and Neptune in the east in the morning sky.
At midmonth, Mercury can be seen during morning twilight, Venus rises at 6:00 a.m., Mars rises at 11:00 p.m. and transits the meridian at 4:00 a.m., Jupiter transits the meridian at 10:00 p.m. and sets at 5:00 a.m., and Saturn rises at midnight and transits the meridian at 4:00 a.m. local daylight time for observers at latitude 40 degrees north.
Mars, Saturn, the waning gibbous Moon, and Antares are in quasi-conjunction on the morning of April 25th. The four celestial objects fit within a circle ten degrees in diameter. The Moon lies north of Mars and Saturn and Antares is south of the two planets and the Moon.
Mercury is at perihelion on April 5th. A waxing crescent Moon passes within eight degrees of the planet on April 8th. Mercury reaches greatest eastern elongation on April 18th, when it will shine at magnitude 0 and attain a sunset altitude of 19 degrees at latitude 40 degrees north. Mercury is illuminated approximately 38% and subtends approximately 7.5 arc seconds on that date. It is still 10 degrees above the west-northwestern horizon 45 minutes after sunset. Due to the tilt of tilt of the ecliptic in the spring, this will be the finest apparition of the planet of 2016 for those living in mid-northern latitudes.
Venus heads sunward as the month progresses. It rises less than 30 minutes before the Sun in early April. The brightest planet is occulted by the Moon on April 6th. Venus decreases slightly in apparent size from 10.3 to 9.8 arc seconds, while remaining fairly constant in illumination and brightness, over the course of the month.
Mars brightens from magnitude -0.5 to magnitude -1.4 and grows in apparent size from 11.8 arc seconds to 16.0 arc seconds, the biggest it has appeared in a decade, this month. It exits Scorpius and enters Ophiuchus on April 3rd. On April 16th, the apparent brightness of Mars exceeds magnitude -1.0. The next day, April 17th, the Red Planet is stationary and starts its retrograde opposition loop, as the Earth passes between Mars and the Sun. Saturn and Mars will be seven degrees apart on that date. Mars is greater than 15 arc seconds in apparent diameter on April 23rd. On April 28th, the Red Planet passes the descending node and is south of the ecliptic. The waning gibbous Moon passes five degrees north of Mars on the morning of April 25th. Mars departs Ophiuchus and reenters Scorpius on April 30th. An article on observing the Mars during its 2016 apparition can be found on pages 48-50 of the April issue of Sky & Telescope.
Jupiter retrogrades through Leo this month. It passes two degrees north of the Moon on April 18th. Jupiter shrinks in apparent diameter from 43.6 to 40.9 arc seconds and decreases in brightness from magnitude -2.4 to magnitude -2.3 during the course of the month. The gas giant passes seven arc minutes north of the fifth-magnitude star Chi Leonis, which may be mistaken for a Galilean satellite, on April 8th. A number of Galilean satellite events take place on the night of April 6th/7th. Io begins a transit of Jupiter at 9:52 p.m. EDT on April 6th. Io’s shadow falls on the planet at 10:32 p.m. EDT. At 10:48 p.m. EDT, Europa is occulted by Jupiter. A transit by Ganymede commences at 1:01 a.m. EDT on April 7th. Europa reappears from eclipse by Jupiter’s shadow at 2:54 a.m. EDT. A shadow transit by Ganymede commences at 3:45 a.m. EDT. Data on other Galilean satellite events is available at 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 51 of the April issue of Sky & Telescope.
Saturn brightens to magnitude +0.2 this month. Its rings span 40 arc seconds and are tilted 26 degrees with respect to the Earth. The waning gibbous Moon passes three degrees north of the Ringed Planet on April 25th. Titan, Saturn’s largest satellite, is due north of the planet on April 3rd and April 19th and due south of it on April 11th and April 27th. Iapetus shines at tenth magnitude and lies nine arc minutes from the planet at greatest western elongation on April 5th. By April 25th, the peculiar satellite has dimmed to eleventh magnitude as it passes two arc minutes north of Saturn. For further information on Saturn’s satellites, browse www.skyandtelescope.com/observing/interactive-sky-watching-tools/
Uranus is in conjunction with the Sun on April 9th and consequently is not observable from the northern hemisphere this month.
Neptune lies 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 www.nakedeyeplanets.com/
Asteroid 6 Hebe glides northwestward through the constellation of Leo this month. The tenth magnitude asteroid passes less than three degrees north of the second-magnitude star Denebola (Beta Leonis). On April 27th, asteroid 3 Juno (magnitude +10.0) reaches opposition in Virgo. The faint asteroid 216 Kleopatra (magnitude +12.7) occults a 10.9-magnitude star in Libra for as much as12 seconds on the morning of April 5th. The event is visible along a track extending from Florida to North Dakota. Click on asteroidoccultation.com/2016_04_si.htm respectively for further information on this and other asteroid occultations taking place this month. See www.curtrenz.com/asteroids.html for additional current information on asteroids.
Visit cometchasing.skyhound.com/ and 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 www.curtrenz.com/astronomical and nineplanets.org/
A free star map for April can be downloaded at www.skymaps.com/downloads.html and www.telescope.com/content.jsp?pageName=Monthly-Star-Chart
The fifth-magnitude G-type main-sequence star 61 Virginis - 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 2nd, 5th, 7th, 10th, 13th, 16th, 19th, 22nd, 25th, 27th, and 30th. For more on Algol, see stars.astro.illinois.edu/sow/Algol.html and www.solstation.com/stars2/algol3.htm
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.