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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.

Mercury evening apparition as seen from latitudes of 52N, 45 minutes after sunset

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.

Venus is a brilliant evening star this month (www.freestarcharts.com)

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

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.

Saturn imaged by the Hubble Space Telescope in October 1998 (NASA, The Hubble Heritage Team (AURA/STScI))

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

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

Neptune during April 2015 - pdf format

Solar System Data Table April 2015

 DateRight AscensionDeclinationApparent MagnitudeApparent SizeIllum. (%)Distance from Earth (AU)Constellation
Sun5th Apr 201500h 54m 04.3s05d 47m 10.1s-26.732.0'1001.000Pisces
Sun15th Apr 201501h 30m 46.9s09d 29m 43.7s-26.731.9'1001.003Pisces
Sun25th Apr 201502h 08m 04.2s12d 56m 37.2s-26.731.8'1001.006Aries
Mercury5th Apr 201500h 36m 30.4s02d 16m 06.1s-1.505.0"981.344Cetus
Mercury15th Apr 201501h 51m 16.4s11d 24m 18.2s-1.805.2"981.299Aries
Mercury25th Apr 201503h 07m 51.0s19d 21m 57.4s-1.006.0"751.128Aries
Venus5th Apr 201503h 17m 02.4s19d 20m 45.3s-4.014.1"771.182Aries
Venus15th Apr 201504h 05m 25.1s22d 30m 58.1s-4.115.0"731.114Taurus
Venus25th Apr 201504h 54m 50.5s24d 43m 51.7s-4.116.0"701.043Taurus
Mars5th Apr 201502h 03m 11.7s12d 25m 43.3s1.403.9"992.378Aries
Mars15th Apr 201502h 31m 34.5s14d 56m 29.8s1.403.9"992.414Aries
Mars25th Apr 201503h 00m 16.4s17d 12m 19.0s1.403.8"992.448Aries
Jupiter5th Apr 201509h 00m 34.1s18d 00m 12.5s-2.341.0"994.811Cancer
Jupiter15th Apr 201509h 00m 43.0s17d 58m 43.9s-2.239.8"994.958Cancer
Jupiter25th Apr 201509h 02m 06.6s17d 51m 57.3s-2.238.6"995.113Cancer
Saturn5th Apr 201516h 11m 06.2s-18d 53m 49.4s0.317.9"1009.294Scorpius
Saturn15th Apr 201516h 09m 23.2s-18d 48m 06.3s0.218.1"1009.177Scorpius
Saturn25th Apr 201516h 07m 08.1s-18d 41m 11.1s0.118.3"1009.084Scorpius
Uranus5th Apr 201501h 00m 29.9s05d 46m 49.9s5.903.4"10020.999Pisces
Uranus15th Apr 201501h 02m 37.0s05d 59m 59.2s5.903.4"10020.991Pisces
Uranus25th Apr 201501h 04m 42.1s06d 12m 50.7s5.903.4"10020.957Pisces
Neptune5th Apr 201522h 41m 19.8s-09d 06m 09.3s8.002.2"10030.767Aquarius
Neptune15th Apr 201522h 42m 28.5s-08d 59m 34.0s8.002.2"10030.657Aquarius
Neptune25th Apr 201522h 43m 29.0s-08d 53m 49.9s7.902.2"10030.527Aquarius