Mercury reaches greatest elongation west (GEW) on April 11th when it will be situated 27 degrees from the Sun in the morning sky. From northern temperate latitudes, the planet is not well placed for observation, and even at GEW it hugs the east-southeastern horizon just before sunrise, shining at magnitude +0.4. Much brighter Venus (mag. -3.9) lies a few degrees from Mercury. Both planets battle against the bright twilight sky.
From southern and equatorial latitudes, early morning observers are rewarded with great opportunities to spot Mercury as it shares the view with Venus. Much fainter Neptune, mag. +8.0, is also in same region of sky. On April 2nd, Neptune appears only 0.4 degrees south of Mercury (mag. +0.8) with the thin crescent Moon 4 degrees to the south. Mercury and Venus are at their closest on April 16th, when just over 4 degrees apart, with both planets visible throughout the month.
Venus shines at magnitude -3.9 throughout April. As the month progresses its angular size reduces from 13.1 to 11.6 arc seconds with its illuminated disk increasing from 81% to 86%. From northern locations, Venus hugs the horizon just before sunrise and by months end will be difficult to spot.
As previously mentioned, from southern and equatorial latitudes, Venus and Mercury are well placed in the morning sky this month with much fainter Neptune also nearby.
Mars remains visible after sunset throughout April. The red planet is now towards the lower end of its brightness scale and fades from magnitude +1.5 to +1.6 this month. From northern temperate locations, it still sets over 3 hours after the Sun by months end. However, those located further south don't have it quite so good with a visibility period of up to 2 hours less.
Mars is currently moving through Taurus and is between the Pleaides (M45) and Hyades open clusters during the first week of the month. On April 9th, the thin waxing crescent passes 5 degrees south of Mars. A week later Mars passes 7 degrees north of first magnitude star, Aldebaran (mag. +0.9).
Jupiter now rises about an hour after midnight at the beginning of the month from northern temperate latitudes and even earlier for those located further south. The gas giant is located in Ophiuchus and brightens from magnitude -2.3 to -2.5, with its apparent size increasing from 39.8 to 43.4 arc seconds as the month progresses. With binoculars or small telescopes up to 4 Galilean moons are visible. A small scope will also reveal features such as the northern and southern equatorial bands and the Great Red Spot, although it has been diminishing in size for some time now.
Saturn starts the month as a morning object in Sagittarius. The planet's magnitude increases slightly from +0.5 to +0.4 as the month progresses, with its apparent diameter improving from 16.4 to 17.2 arc seconds.
Due to its southerly latitude, Saturn is much better placed from southern latitudes. From such locations it rises late evening by months end, although a few hours later for those located further north. The waning crescent Moon occults Saturn on April 25th from southern Africa, Madagascar and east South America. On the last day of the month, Saturn begins retrograde motion.
Uranus reaches solar conjunction on April 23rd and is therefore positioned too close to the Sun to be safely observed this month.
Neptune, mag. +8.0, is located in the faint Aquarius and passed through solar conjunction at the beginning of last month. From northern temperate latitudes, the distant planet remains unsuitably placed for observation throughout April but can be seen before sunrise towards the east from equatorial and southern regions. As mentioned previously, Mercury and Venus are positioned in the same region of sky. By months end, from such locations, it rises up to four hours before the Sun.
Although never bright enough to be seen with the naked eye, Neptune can be spotted with binoculars under dark skies. On April 30th, the thin waning crescent Moon passes 4 degrees south of Neptune.
Solar System Data Table - April 2019
|Date||Right Ascension||Declination||Mag.||App. Size||Illum. (%)||Dist. (AU)||Constellation|
|Sun||Apr 01||00h 39m 24.7s||04d 14m 31.7s||-26.7||32.0'||100||0.999||Pisces|
|Sun||Apr 15||01h 30m 43.5s||09d 29m 22.6s||-26.7||31.9'||100||1.003||Pisces|
|Sun||Apr 30||02h 26m 54.5s||14d 31m 58.1s||-26.7||31.8'||100||1.007||Aries|
|Mercury||Apr 01||23h 10m 12.1s||-05d 35m 43.1s||0.8||9.4"||29||0.718||Aquarius|
|Mercury||Apr 15||23h 53m 08.1s||-03d 19m 46.8s||0.2||7.3"||53||0.916||Aquarius|
|Mercury||Apr 30||01h 10m 17.4s||04d 41m 47.3s||-0.3||5.9"||74||1.135||Pisces|
|Venus||Apr 01||22h 32m 22.8s||-10d 09m 47.8s||-3.9||13.1"||81||1.274||Aquarius|
|Venus||Apr 15||23h 36m 02.7s||-04d 06m 34.3s||-3.9||12.3"||85||1.357||Aquarius|
|Venus||Apr 30||00h 43m 10.7s||02d 51m 07.7s||-3.9||11.6"||88||1.440||Pisces|
|Mars||Apr 01||03h 51m 24.4s||21d 05m 41.3s||1.4||4.6"||94||2.020||Taurus|
|Mars||Apr 15||04h 30m 30.0s||22d 51m 26.5s||1.5||4.4"||95||2.126||Taurus|
|Mars||Apr 30||05h 12m 57.1s||24d 04m 10.4s||1.6||4.2"||96||2.232||Taurus|
|Jupiter||Apr 01||17h 33m 42.6s||-22d 39m 57.1s||-2.3||39.8"||99||4.947||Ophiuchus|
|Jupiter||Apr 15||17h 34m 13.1s||-22d 40m 09.4s||-2.4||41.6"||99||4.739||Ophiuchus|
|Jupiter||Apr 30||17h 31m 51.0s||-22d 38m 46.4s||-2.5||43.4"||100||4.547||Ophiuchus|
|Saturn||Apr 01||19h 24m 28.6s||-21d 36m 10.2s||0.5||16.4"||100||10.161||Sagittarius|
|Saturn||Apr 15||19h 26m 35.5s||-21d 32m 22.2s||0.5||16.7"||100||9.928||Sagittarius|
|Saturn||Apr 30||19h 27m 22.6s||-21d 31m 20.7s||0.4||17.2"||100||9.683||Sagittarius|
|Uranus||Apr 01||01h 56m 16.5s||11d 22m 09.6s||5.9||3.4"||100||20.786||Aries|
|Uranus||Apr 15||01h 59m 16.6s||11d 38m 38.1s||5.9||3.4"||100||20.844||Aries|
|Uranus||Apr 30||02h 02m 34.3s||11d 56m 27.2s||5.9||3.4"||100||20.849||Aries|
|Neptune||Apr 01||23h 13m 02.6s||-06d 05m 30.3s||8.0||2.2"||100||30.848||Aquarius|
|Neptune||Apr 15||23h 14m 47.7s||-05d 54m 49.2s||8.0||2.2"||100||30.730||Aquarius|
|Neptune||Apr 30||23h 16m 25.4s||-05d 45m 02.0s||7.9||2.2"||100||30.555||Aquarius|