Mercury is visible as an evening object for observers at northern and equatorial latitudes during April (apart from the few days at the start and end of the month). For this apparition the planet can be seen low down above the west-northwestern horizon just after sunset. The peak altitude occurs on April 18th when greatest elongation east (GEE) is reached. On this day, from London for example, the planet will be visible as a mag. -0.1 point of light 10 degrees above the horizon, 45 minutes after sunset. Observers should also note that Mercury is at its brightest at the start of the month and before GEE occurs. It decreases from mag. -1.4 to +2.1 during the visibility period.
On April 8th the thin waxing crescent Moon passes 5 degrees south of Mercury, aiding in locating the planet.
The chart below shows positions of Mercury during April from latitude 52N (e.g. London, England). The view will be similar from other northern temperate locations with the added bonus this is the most favourable evening apparition of the year from such regions. From mid-southern latitudes, Mercury is not suitably placed for observation this month.
Venus, mag. -3.8, is now too close to the Sun to be seen from mid-northern temperature latitudes although from equatorial and southern latitudes it can be spotted throughout April low down above the eastern horizon just before sunrise. However, the planet is now fast closing in towards the Sun and during May will be finally lost to the bright twilight from all remaining locations Worldwide.
An interesting occultation occurs on April 6th when the thin 2% illuminated waning crescent Moon passes 0.7 degrees north of Venus. Since the event occurs during daytime we don't recommend viewing it as the Sun is dangerously close by.
Mars is now a bright conspicuous object that starts the month in Scorpius before moving into neighbouring Ophiuchus (April 3rd). With a southerly declination of 21 degrees the famous "Red planet" is rather more favorably seen from southern locations where at the beginning of the month it rises during late evening, improving to early evening by months end. From mid-northern latitudes the planet is visible almost three hours later than that. On April 17th, Mars reaches its first stationary point after which retrograde motion commences.
To the naked eye Mars appears a deep red-orange in colour. Since there are only a few weeks to go until opposition it's now brightening nicely, increasing from mag. -0.5 to -1.4 as the month progresses. The surrounding region of sky also contains first magnitude red supergiant star Antares (α Sco - mag. +1.0) located 6 degrees southeast of Mars and Saturn (mag. +0.3) about 10 degrees east of the planet. Of the three objects Mars is easily the brightest followed by Saturn and then Antares.
When viewed through a telescope Mars appears small - its apparent size increases from 12 to 16 arc seconds this month - but under good seeing conditions it's possible to spot major surface features such as the North Pole cap, Syrtis Major and other dusty markings. A good tip is to push up the magnification as high as possible to tease out subtle details.
On April 25th the waning gibbous Moon passes 5 degrees north of Mars.
Jupiter is now just a month past opposition and continues to be a stunning object moving retrograde among the stars of Leo. The giant planet is visible towards the east as soon as it's dark enough and remains so until the early hours of the morning. Jupiter starts April at magnitude -2.4 with an apparent diameter 44 arc seconds. By months end it has faded slightly to mag. -2.3 and shrunk to 41 arc seconds in diameter.
When viewed through a telescope a wealth of planetary details are visible including cloud bands, twists, knots and storms with the most famous of all being "The Great Red Spot". Also easily visible but not always at the same time are the four bright Galilean moons: Io, Europa, Ganymede and Callisto.
A lovely pairing occurs on the night of April 17th/18th when the waxing gibbous Moon passes just a couple of degrees south of Jupiter.
Saturn is positioned about 10 degrees east of Mars as it continues to move slowly retrograde in Ophiuchus. The beautiful "Ringed planet" rises an hour or so after Mars and by months end can be seen before midnight from northern temperate latitudes and up to three hours earlier for those living further south.
At the beginning of April a good opportunity exists to spot bizarre moon Iapetus. This world is famous for its "two-tone" colouration with one side much darker in colour than the other. As a result when Iapetus is positioned on the western side of Saturn (as viewed from Earth) it appears brighter than when positioned on the opposite side. On April 5th, Iapetus reaches greatest western elongation and at mag. +10.1 can be seen with a small scope of 80mm (3.1-inch) aperture.
The Solar System's second largest planet increases slightly in brightness from magnitude +0.4 to +0.2 with its apparent diameter improving from 17.4 to 18.1 arc seconds as the month progresses. On April 25th, the waning gibbous Moon passes 3 degrees north of Saturn.
Uranus reaches solar conjunction on April 9th and therefore is positioned too close to the Sun to be safely observed this month.
Neptune, mag. +8.0, reached solar conjunction at the end of February but from northern temperate latitudes remains unsuitably placed for observation during April. However it can be seen before sunrise towards the east from equatorial and southern regions. By months end the planet rises up to four hours before the Sun from such locations.
The ice giant and most distant of the eight planets is currently located in the faint constellation of Aquarius. It's never bright enough to be seen with the naked eye but can be spotted with binoculars when the sky is dark enough.
On April 5th the thin waning crescent Moon passes 2 degrees north of Neptune.
Solar System Data Table April 2016
|Date||Right Ascension||Declination||Apparent Magnitude||Apparent Size||Illum. (%)||Distance from Earth (AU)||Constellation|
|Sun||5th Apr 2016||00h 56m 47.8s||06d 04m 10.4s||-26.7||32.0'||100||1.000||Pisces|
|Sun||15th Apr 2016||01h 33m 33.1s||09d 45m 49.0s||-26.7||31.9'||100||1.003||Pisces|
|Sun||25th Apr 2016||02h 10m 52.0s||13d 11m 12.3s||-26.7||31.8'||100||1.006||Aries|
|Mercury||5th Apr 2016||01h 42m 40.6s||11d 26m 25.6s||-1.3||05.6"||85||1.194||Pisces|
|Mercury||15th Apr 2016||02h 44m 52.0s||18d 28m 55.9s||-0.4||07.0"||51||0.955||Aries|
|Mercury||25th Apr 2016||03h 18m 16.7s||21d 09m 25.1s||1.3||09.3"||20||0.724||Aries|
|Venus||5th Apr 2016||23h 58m 22.8s||-01d 47m 59.5s||-3.8||10.2"||96||1.628||Pisces|
|Venus||15th Apr 2016||00h 43m 43.5s||03d 05m 22.7s||-3.8||10.1"||97||1.658||Pisces|
|Venus||25th Apr 2016||01h 29m 21.8s||07d 53m 18.2s||-3.9||09.9"||98||1.684||Pisces|
|Mars||5th Apr 2016||16h 24m 28.6s||-20d 49m 30.1s||-0.7||12.4"||93||0.757||Ophiuchus|
|Mars||15th Apr 2016||16h 27m 57.8s||-21d 14m 09.0s||-1.0||13.8"||95||0.681||Ophiuchus|
|Mars||25th Apr 2016||16h 26m 24.6s||-21d 32m 10.2s||-1.3||15.2"||97||0.615||Ophiuchus|
|Jupiter||5th Apr 2016||11h 06m 14.6s||07d 20m 14.4s||-2.4||43.4"||100||4.548||Leo|
|Jupiter||15th Apr 2016||11h 03m 01.6s||07d 38m 51.7s||-2.4||42.5"||100||4.640||Leo|
|Jupiter||25th Apr 2016||11h 00m 48.2s||07d 50m 52.0s||-2.3||41.5"||99||4.754||Leo|
|Saturn||5th Apr 2016||17h 00m 20.2s||-20d 56m 50.4s||0.4||17.5"||100||9.494||Ophiuchus|
|Saturn||15th Apr 2016||16h 59m 15.7s||-20d 54m 19.2s||0.4||17.8"||100||9.357||Ophiuchus|
|Saturn||25th Apr 2016||16h 57m 33.6s||-20d 51m 01.2s||0.3||18.0"||100||9.238||Ophiuchus|
|Uranus||5th Apr 2016||01h 14m 35.0s||07d 15m 04.2s||5.9||03.4"||100||20.964||Pisces|
|Uranus||15th Apr 2016||01h 16m 43.1s||07d 28m 01.6s||5.9||03.4"||100||20.965||Pisces|
|Uranus||25th Apr 2016||01h 18m 50.0s||07d 40m 45.6s||5.9||03.4"||100||20.940||Pisces|
|Neptune||5th Apr 2016||22h 49m 31.2s||-08d 20m 33.3s||8.0||02.2"||100||30.773||Aquarius|
|Neptune||15th Apr 2016||22h 50m 40.8s||-08d 13m 46.6s||8.0||02.2"||100||30.666||Aquarius|
|Neptune||25th Apr 2016||22h 51m 42.3s||-08d 07m 50.7s||7.9||02.2"||100||30.540||Aquarius|