Mercury
During April, Mercury remains well placed for observation before dawn for observers located in the tropics and at southern hemisphere latitudes. For those at northern temperate latitudes, the angle of the ecliptic is unfavourable and the planet is not visible this month.
On March 31st, the closest planet to the Sun reached greatest elongation west (28 degrees from the Sun). On this date, from latitudes of 35S (approx. equal to Sydney, Cape Town and Santiago) it was positioned 20 degrees above the eastern horizon, 30 minutes before sunrise.
The planets altitude will slightly decrease each subsequent morning as the month progresses but at the same time it increases in brightness. Mercury starts April at magnitude 0.3 and finishes the month at magnitude -1.0.
On April 8th, the thin waning crescent Moon will pass 7 degrees north of Mercury and on April 19th, Mercury will be positioned 2 degrees south of Uranus (mag. 5.9).
The diagram below shows the March and April morning apparition of Mercury from latitude of 35S.
Venus
Venus passed through superior conjunction on March 28th. The planet is now located on the far side of the Sun and consequently unsuitably placed for observation throughout April.
Mars
Mars reaches solar conjunction on April 18th and therefore is positioned too close to the Sun to be observed this month.
Jupiter
Jupiter remains an evening object throughout April. The largest planet of the solar system is visible in the southwest sky as soon as it gets dark, but now sets before midnight by months end from northern temperate latitudes. The period of visibility is even less for those located further south.
The giant planet continues it direct motion in Taurus. At the start of April it's positioned only 5.5 degrees north of magnitude 0.9 orange/red star Aldebaran and the famous "V" shaped Hyades open cluster. By the end of the month Jupiter has moved to 9 degrees northeast of Aldebaran and continues to gradually drift away from this prime section of zodiac "real estate".
The planets magnitude decreases from -2.1 to -2.0 during April with the apparent size diminishing from 36 to 34 arc seconds over the same time period. On April 14th, the waxing crescent Moon passes 2 degrees south of Jupiter between the "horns" of Taurus, the Bull.
Jupiter in Taurus during April 2013 - pdf format
Saturn
Saturn reaches opposition on April 28th (mag. 0.1) and on this date is located 8.816 AU (approx. 1319 million km or 819.5 million miles) from Earth. It rises towards the east-southeast and is visible as soon as it gets darks and remains so all-night. The far away planet with its beautiful set of rings, is currently moving retrograde amongst the faint stars of western Libra.
During April, the brightness of Saturn increases slightly from magnitude 0.3 to 0.1, with an apparent diameter of 19 arc seconds.
From our perspective, Saturn's rings are titled at approx. 19 degrees and are a wonderful sight through telescopes. They are visible in even the smallest of instruments and are a must see on all astronomers observation lists. Larger telescopes reveal subtle details, with many of the planets brightest moons visible.
The full Moon passes 4 degrees south of Saturn on April 26th.
Saturn in Libra during April 2013 - pdf format
Uranus
In Pisces, for northern hemisphere observers not suitably placed for observation during April, but visible as a very early morning object during the second half of the month for those located further south.
Uranus shines at magnitude 5.9 and on April 19th, Mercury (magnitude -0.3) passes 2 degrees south of the very distant green planet, just before sunrise.
Neptune
Neptune, magnitude 8.0, is currently located in Aquarius. It remains unsuitably placed for observation throughout April from the northern hemisphere but can be seen in the early morning sky from tropical and southern latitudes.
Solar System Data Table April 2013
| Date | Right Ascension | Declination | Mag. | Size | Illum. (%) | Distance from Earth (AU) | Constellation | |
|---|---|---|---|---|---|---|---|---|
| Sun | 5th Apr 2013 | 00h 55m 55.9s | 05d 58m 47.6s | -26.7 | 32.0' | 100 | 1.000 | Pisces |
| Sun | 15th Apr 2013 | 01h 32m 40.6s | 09d 40m 44.4s | -26.7 | 31.9' | 100 | 1.003 | Pisces |
| Sun | 25th Apr 2013 | 02h 09m 58.9s | 13d 06m 35.1s | -26.7 | 31.8' | 100 | 1.006 | Aries |
| Mercury | 5th Apr 2013 | 23h 18m 20.9s | -06d 43m 54.0s | 0.1 | 07.1" | 57 | 0.950 | Aquarius |
| Mercury | 15th Apr 2013 | 00h 08m 17.2s | -01d 56m 01.9s | -0.1 | 06.2" | 70 | 1.091 | Pisces |
| Mercury | 25th Apr 2013 | 01h 07m 41.4s | 04d 45m 24.8s | -0.5 | 05.5" | 83 | 1.218 | Pisces |
| Venus | 5th Apr 2013 | 01h 04m 40.6s | 05d 35m 14.7s | -4.0 | 09.7" | 100 | 1.724 | Pisces |
| Venus | 15th Apr 2013 | 01h 50m 49.9s | 10d 23m 35.7s | -3.9 | 09.7" | 100 | 1.720 | Pisces |
| Venus | 25th Apr 2013 | 02h 38m 11.9s | 14d 47m 36.7s | -3.9 | 09.8" | 99 | 1.710 | Aries |
| Mars | 5th Apr 2013 | 01h 07m 35.0s | 06d 36m 23.1s | 1.2 | 03.9" | 100 | 2.414 | Pisces |
| Mars | 15th Apr 2013 | 01h 35m 52.5s | 09d 31m 34.5s | 1.2 | 03.9" | 100 | 2.428 | Pisces |
| Mars | 25th Apr 2013 | 02h 04m 20.1s | 12d 16m 10.3s | 1.2 | 03.8" | 100 | 2.441 | Aries |
| Jupiter | 5th Apr 2013 | 04h 43m 39.2s | 21d 53m 39.3s | -2.1 | 35.4" | 99 | 5.567 | Taurus |
| Jupiter | 15th Apr 2013 | 04h 51m 21.3s | 22d 08m 31.6s | -2.0 | 34.6" | 99 | 5.698 | Taurus |
| Jupiter | 25th Apr 2013 | 04h 59m 41.3s | 22d 22m 47.2s | -2.0 | 33.9" | 100 | 5.814 | Taurus |
| Saturn | 5th Apr 2013 | 14h 32m 40.6s | -12d 11m 29.3s | 0.2 | 18.7" | 100 | 8.898 | Libra |
| Saturn | 15th Apr 2013 | 14h 30m 00.5s | -11d 57m 40.0s | 0.2 | 18.8" | 100 | 8.843 | Libra |
| Saturn | 25th Apr 2013 | 14h 27m 07.9s | -11d 43m 14.3s | 0.1 | 18.8" | 100 | 8.818 | Libra |
| Uranus | 5th Apr 2013 | 00h 33m 02.0s | 02d 50m 04.4s | 5.9 | 03.3" | 100 | 21.046 | Pisces |
| Uranus | 15th Apr 2013 | 00h 35m 06.3s | 03d 03m 19.6s | 5.9 | 03.4" | 100 | 21.015 | Pisces |
| Uranus | 25th Apr 2013 | 00h 37m 06.4s | 03d 16m 03.2s | 5.9 | 03.4" | 100 | 20.958 | Pisces |
| Neptune | 5th Apr 2013 | 22h 25m 04.5s | -10d 33m 55.7s | 8.0 | 02.2" | 100 | 30.735 | Aquarius |
| Neptune | 15th Apr 2013 | 22h 26m 09.9s | -10d 27m 54.4s | 7.9 | 02.2" | 100 | 30.615 | Aquarius |
| Neptune | 25th Apr 2013 | 22h 27m 06.1s | -10d 22m 46.8s | 7.9 | 02.2" | 100 | 30.476 | Aquarius |