Mercury
Mercury reaches superior conjunction on April 10th and is therefore too close to the Sun to be seen at this time. However it doesn't take long before the fast moving planet reappears in the early evening sky. From northern and equatorial latitudes, it's visible from about April 21st or so, low down above the west-northwestern horizon just after sunset. For northern observers this also happens to be the most favourable evening apparition of the year.
The following day Mercury (mag. -1.4) passes just over a degree north of Mars (mag. +1.4). Binoculars will show both objects in the same field of view with Mercury 15 times the brighter. A 200mm (8-inch) telescope at medium to high magnification should reveal the disks of both planets although they are both small (Mercury 5.7 arc seconds, Mars 3.8 arc seconds). In the same region of sky and positioned a few degrees to the northeast of the pair is much more brilliant Venus (mag. -4.1).
Mercury then continues to climb higher each subsequent evening, although at the same time fading in brightness, until it reaches greatest eastern elongation on May 7th. From the Southern Hemisphere the planet is nowhere near as well placed for observation but may still be glimpsed extremely low down above the west-northwestern horizon just after sunset towards the end of the month.
The chart below shows positions of Mercury and Venus from latitude 52N (e.g. London, England). The view will be similar from other northern temperate locations.
Venus
Brilliant Venus, mag. -4.1, continues to dominate the western sky after sunset. The unmistakable planet is visible as soon as dark enough although the period of visibility varies considerably depending on location. From northern temperate latitudes Venus sets almost 3.5 hours after the Sun at the start of the month, increasing to 4 hours by months end. However, much further south the planet can be seen for as little as 2 hours.
On April 11th, Venus passes 2.5 degrees south of beautiful open cluster the Pleiades (M45). This grouping makes a wonderful pairing for binoculars or wide-field telescopes. Later in the month (April 21st) it's located 7.5 degrees north of Aldebaran and another open cluster, the large sprawling Hyades. On the same evening the waxing crescent Moon passes 7 degrees south of Venus.
Mars
The long Mars period of visibility finally comes to an end in April. For sometime now the famous Red planet has kept ahead of the Sun in the early evening sky but this month it's eventually lost to the bright twilight. From Northern Hemisphere latitudes the planet can be glimpsed just after sunset towards the west during the first half of April. With an apparent magnitude of +1.4 it's looks like an unremarkable first magnitude "star". On April 22nd, Mercury (mag. -1.4) passes just over a degree north of Mars (mag. +1.4).
From southern latitudes, Mars is to all intent and purpose only visible during the first few evenings of the month.
Jupiter
Jupiter is now two months past opposition and despite fading in brightness it remains a brilliant evening object. As soon as darkness falls, the Solar System's largest and dominant planet is easily recognisable as a bright beacon of light amongst the faint stars of Cancer. From latitudes of Northern Europe and America, the giant planet sets after midnight by months end although the period of visibility is much reduced for those located further south.
Jupiter begins the month moving retrograde until April 8th when it reaches its second and final stationary point for 2015. After this direct motion (eastward) is again resumed with the event widely regarded as signalling the end of the opposition period. To the unaided eye, Jupiter will essentially appear stationary during April. However during the upcoming months direct motion will be obvious as it finally leaves Cancer and marches on towards Leo and Regulus.
On April 1st, Jupiter shines at magnitude -2.3 with an apparent diameter of 41 arc minutes. At the end of April the brightness has decreased to magnitude -2.1 and the apparent diameter to 38 arc minutes.
The waxing gibbous Moon (57% illuminated) passes 6 degrees south of Jupiter on April 26th.
Jupiter during April 2015 - pdf format
Saturn
Saturn continues to move slowly retrograde in northern Scorpius. The stunning "Ringed Planet" is located near the stars of the Scorpion "Sting" as it heads towards next month opposition. Saturn rises during the evening and remains visible for the rest of the night although it can be seen for considerably longer from equatorial and Southern Hemisphere latitudes. The planet also appears higher in the sky from such locations.
To the naked eye Saturn appears creamy in colour. It makes a nice contrast compared to the orange/red hue of first magnitude red giant Antares (α Sco mag. +1.0) located 8 degrees to the southeast. Through a telescope the planets rings are a beautiful sight. They are visible with just a small instrument and currently tilted so that they are wide open (tilted at 24 degrees). A medium size telescope of 150mm (6-inch) or 200mm (8-inch) aperture will show a wealth of details including subtle planet formations, divisions in the rings as well as up to half a dozen of Saturn's satellites.
During the month, Saturn brightens slightly from magnitude +0.3 to +0.1 with it apparent size increasing marginally from 17.8 to 18.4 arc seconds. On April 8th, the waning gibbous Moon passes 2 degrees north of Saturn.
Saturn during April 2015 - pdf format
Uranus
Uranus reaches solar conjunction on April 6th and is therefore unsuitably placed for observation throughout April.
Neptune
Neptune, mag. +8.0, reached solar conjunction at the end of February but remains unsuitably placed for observation from northern temperate latitudes during April. However, it can be seen in the early morning sky towards the east from equatorial and southern regions. By months end it rises up to four hours before the Sun from such locations.
The outermost planet of all is currently located in the faint constellation of Aquarius. Neptune never comes close to naked eye brightness though it can be seen with binoculars or small telescopes. On April 14th, large asteroid Vesta passes 2.7 degrees south of Neptune. Both objects are of the same magnitude and wide field scopes should easily show them in the same field of view.
The following day, the waning crescent Moon passes 3.6 degrees north of Neptune.
Neptune during April 2015 - pdf format
Solar System Data Table April 2015
| Date | Right Ascension | Declination | Apparent Magnitude | Apparent Size | Illum. (%) | Distance from Earth (AU) | Constellation | |
|---|---|---|---|---|---|---|---|---|
| Sun | 5th Apr 2015 | 00h 54m 04.3s | 05d 47m 10.1s | -26.7 | 32.0' | 100 | 1.000 | Pisces |
| Sun | 15th Apr 2015 | 01h 30m 46.9s | 09d 29m 43.7s | -26.7 | 31.9' | 100 | 1.003 | Pisces |
| Sun | 25th Apr 2015 | 02h 08m 04.2s | 12d 56m 37.2s | -26.7 | 31.8' | 100 | 1.006 | Aries |
| Mercury | 5th Apr 2015 | 00h 36m 30.4s | 02d 16m 06.1s | -1.5 | 05.0" | 98 | 1.344 | Cetus |
| Mercury | 15th Apr 2015 | 01h 51m 16.4s | 11d 24m 18.2s | -1.8 | 05.2" | 98 | 1.299 | Aries |
| Mercury | 25th Apr 2015 | 03h 07m 51.0s | 19d 21m 57.4s | -1.0 | 06.0" | 75 | 1.128 | Aries |
| Venus | 5th Apr 2015 | 03h 17m 02.4s | 19d 20m 45.3s | -4.0 | 14.1" | 77 | 1.182 | Aries |
| Venus | 15th Apr 2015 | 04h 05m 25.1s | 22d 30m 58.1s | -4.1 | 15.0" | 73 | 1.114 | Taurus |
| Venus | 25th Apr 2015 | 04h 54m 50.5s | 24d 43m 51.7s | -4.1 | 16.0" | 70 | 1.043 | Taurus |
| Mars | 5th Apr 2015 | 02h 03m 11.7s | 12d 25m 43.3s | 1.4 | 03.9" | 99 | 2.378 | Aries |
| Mars | 15th Apr 2015 | 02h 31m 34.5s | 14d 56m 29.8s | 1.4 | 03.9" | 99 | 2.414 | Aries |
| Mars | 25th Apr 2015 | 03h 00m 16.4s | 17d 12m 19.0s | 1.4 | 03.8" | 99 | 2.448 | Aries |
| Jupiter | 5th Apr 2015 | 09h 00m 34.1s | 18d 00m 12.5s | -2.3 | 41.0" | 99 | 4.811 | Cancer |
| Jupiter | 15th Apr 2015 | 09h 00m 43.0s | 17d 58m 43.9s | -2.2 | 39.8" | 99 | 4.958 | Cancer |
| Jupiter | 25th Apr 2015 | 09h 02m 06.6s | 17d 51m 57.3s | -2.2 | 38.6" | 99 | 5.113 | Cancer |
| Saturn | 5th Apr 2015 | 16h 11m 06.2s | -18d 53m 49.4s | 0.3 | 17.9" | 100 | 9.294 | Scorpius |
| Saturn | 15th Apr 2015 | 16h 09m 23.2s | -18d 48m 06.3s | 0.2 | 18.1" | 100 | 9.177 | Scorpius |
| Saturn | 25th Apr 2015 | 16h 07m 08.1s | -18d 41m 11.1s | 0.1 | 18.3" | 100 | 9.084 | Scorpius |
| Uranus | 5th Apr 2015 | 01h 00m 29.9s | 05d 46m 49.9s | 5.9 | 03.4" | 100 | 20.999 | Pisces |
| Uranus | 15th Apr 2015 | 01h 02m 37.0s | 05d 59m 59.2s | 5.9 | 03.4" | 100 | 20.991 | Pisces |
| Uranus | 25th Apr 2015 | 01h 04m 42.1s | 06d 12m 50.7s | 5.9 | 03.4" | 100 | 20.957 | Pisces |
| Neptune | 5th Apr 2015 | 22h 41m 19.8s | -09d 06m 09.3s | 8.0 | 02.2" | 100 | 30.767 | Aquarius |
| Neptune | 15th Apr 2015 | 22h 42m 28.5s | -08d 59m 34.0s | 8.0 | 02.2" | 100 | 30.657 | Aquarius |
| Neptune | 25th Apr 2015 | 22h 43m 29.0s | -08d 53m 49.9s | 7.9 | 02.2" | 100 | 30.527 | Aquarius |