Mercury
From equatorial and southern temperate latitudes Mercury can be spotted during the last few days of the month as an early morning object low down above the east-northeastern horizon just before sunrise. From northern temperate latitudes the planet is swamped by the lengthening twilight and is unlikely to be seen.
On May 9th a rare event occurs when Mercury transits the Sun and appears to move across the solar disk. The transit begins at 11:12 UT, ends at 18:42 UT with the midpoint occurring at 14:58 UT. Observers will notice a tiny 10 arc second diameter disk silhouetted against the solar disk.
Extremely important when observing the Sun is to always exercise due care and use only safe observing techniques. Never look at the Sun directly it's incredibly dangerous and will cause permanent eye damage. Observe the transit with either a specialised solar telescope or a normal telescope with approved filters fitted over the main lens or mirror of the instrument. It's not safe to use filters at the eyepiece end. Alternatively, you can project the solar disk onto a shielded white card ensuring that all finderscopes are removed or safely covered.
From eastern North America, Western Europe, Northwestern Africa and much of South America the transit is visible in its entirety. The transit will already have started at sunrise for those living in western North America and the southern part of South America whereas for the rest of Africa and most of Asia it's still in progress at sunset. Finally folks in Australia, New Zealand, Japan and other parts of eastern Asia will have to watch online.
Venus
Venus is no longer visible from northern temperate latitudes. Observers at tropical and Southern Hemisphere locations may be able to glimpse the planet low down against the bright dawn twilight sky just before sunrise during the first 3 weeks of the month.
The planet shines at mag. –3.9 and has an illuminated phase of almost 99%. Its apparent diameter is almost 10 arc seconds.
Mars
Mars reaches opposition in Scorpius on May 22nd and therefore is visible all night long. On this day the planet peaks at mag. –2.1 and for a short time rivals Jupiter in brightness. Due to the considerable eccentricity of its orbit, Mars reaches closest approach to Earth on May 30th when 0.5032 AU (75.279 million kilometres or 46.776 million miles) separates the two planets. This is eight days after opposition.
Naturally this is a superb time for observers of the famous "Red planet". It's at its brightest and largest since 2005 (apparent size peaks at 18.6 arc seconds). A telescope under good seeing conditions at medium / high magnifications will reveal many surface markings. When viewed through a 100mm (4-inch) instrument it's possible to spot the polar cap as well as major surface features such as Syrtis Major. Larger telescopes fair better with more subtle details visible.
The surrounding region of sky also contains first magnitude red supergiant star Antares (α Sco - mag. +1.0) and Saturn (mag. 0.0). Of the three objects Mars is easily the brightest followed by Saturn and then Antares.
On May 21st, the full Moon passes 6 degrees north of Mars. A few days later its retrograde motion moves it into neighbouring constellation Libra (May 28th).
Mars and Saturn during May 2016 - pdf format (credit:- freestarcharts)
Jupiter
Jupiter is now two months past opposition but despite fading remains a brilliant evening object during May. The giant planet is easily recognisable as darkness falls just south of the main stars of Leo. By months end it sets up to a couple of hours after midnight.
Jupiter starts the month moving retrograde until the ninth day when it reaches its second stationary point. After that direct motion (eastward) is resumed. This event is widely regarded as signaling the end of this year's opposition period. To the unaided eye the planet will hardly change position relative to the background stars this month.
On May 1st, Jupiter shines at mag. -2.3 with an apparent diameter of 41 arc seconds. At the end of the month its brightness has decreased to mag. -2.1 with the apparent diameter reduced to 37 arc seconds.
The waxing gibbous Moon (67% illuminated) passes 2 degrees south of Jupiter on May 15th.
Jupiter during May 2016 - pdf format (credit:- freestarcharts)
Saturn
Saturn continues to move retrograde in the constellation of Ophiuchus. The stunning "Ringed Planet" is visible from early evening as is heads towards opposition next month. Due to its current southerly declination the visibility period is considerably longer for those at southern latitudes.
To the naked eye Saturn appears yellowish. Through a telescope its rings are a beautiful sight and even a small refractor/reflector will show them. In addition, a medium size scope of 150mm (6-inch) or 200mm (8-inch) aperture reveals a wealth of details including planetary cloud formations, divisions in the rings and up to half a dozen satellites.
During the month, Saturn brightens from mag. +0.2 to 0.0 with it apparent size increasing marginally from 18.1 to 18.4 arc seconds. On May 22nd, the waning gibbous Moon passes 3 degrees north of the planet.
Uranus
Uranus in Pisces passed by solar conjunction on April 9th. From northern temperate latitudes it remains unsuitably placed for observation throughout May. However those located further south may be able to spot the planet low down above the eastern horizon just before sunrise during the second half of the month. Optical aid is required (mag. +5.9).
On May 5th the thin waning crescent Moon passes 2 degrees south of the planet.
Neptune
Neptune, mag. +7.9, is a morning object from tropical and southern latitudes during May. From such locations the distant planet rises up to four hours before the Sun at start of the month improving to not long after midnight by months end. From Northern temperate latitudes Neptune is poorly placed for observation although it may be spotted low down above the eastern horizon at the tail end of May.
Currently located in Aquarius, Neptune is the only planet that's not visible to the naked eye but it can be seen with binoculars. Locating Neptune is made easier at the moment since it's positioned only 0.5 degrees south of mag. +3.7 star lambda Aqr (λ Aqr).
The waning crescent Moon passes 2 degrees north of Neptune on May 2nd with the last quarter Moon moving 1.4 degrees north of the planet on May 29th.
Neptune during May 2016 - pdf format (credit:- freestarcharts)
Solar System Data Table May 2016
| Date | Right Ascension | Declination | Apparent Magnitude | Apparent Size | Illum.(%) | Distance from Earth (AU) | Constellation | |
|---|---|---|---|---|---|---|---|---|
| Sun | 5th May 2016 | 02h 48m 59.4s | 16d 14m 57.2s | -26.7 | 31.7' | 100 | 1.009 | Aries |
| Sun | 15th May 2016 | 03h 28m 02.8s | 18d 51m 47.7s | -26.7 | 31.6' | 100 | 1.011 | Taurus |
| Sun | 25th May 2016 | 04h 08m 00.8s | 20d 56m 44.6s | -26.7 | 31.6' | 100 | 1.013 | Taurus |
| Mercury | 5th May 2016 | 03h 16m 08.4s | 19d 21m 32.8s | 4.7 | 11.6" | 02 | 0.582 | Aries |
| Mercury | 15th May 2016 | 02h 56m 30.8s | 15d 06m 44.6s | 4.5 | 12.0" | 03 | 0.561 | Aries |
| Mercury | 25th May 2016 | 02h 51m 44.9s | 12d 48m 43.9s | 1.8 | 10.4" | 17 | 0.644 | Aries |
| Venus | 5th May 2016 | 02h 15m 57.1s | 12d 24m 02.4s | -3.9 | 09.8" | 99 | 1.704 | Aries |
| Venus | 15th May 2016 | 03h 04m 00.6s | 16d 25m 30.2s | -3.9 | 09.7" | 99 | 1.720 | Aries |
| Venus | 25th May 2016 | 03h 53m 50.7s | 19d 45m 30.9s | -3.9 | 09.6" | 100 | 1.730 | Taurus |
| Mars | 5th May 2016 | 16h 19m 26.9s | -21d 42m 27.0s | -1.6 | 16.7" | 98 | 0.562 | Scorpius |
| Mars | 15th May 2016 | 16h 07m 37.5s | -21d 42m 51.3s | -1.9 | 17.8" | 100 | 0.526 | Scorpius |
| Mars | 25th May 2016 | 15h 52m 55.2s | -21d 33m 00.4s | -2.0 | 18.5" | 100 | 0.506 | Scorpius |
| Jupiter | 5th May 2016 | 10h 59m 40.2s | 07d 55m 49.6s | -2.2 | 40.4" | 99 | 4.885 | Leo |
| Jupiter | 15th May 2016 | 10h 59m 40.4s | 07d 53m 37.3s | -2.2 | 39.2" | 99 | 5.029 | Leo |
| Jupiter | 25th May 2016 | 11h 00m 47.7s | 07d 44m 28.5s | -2.1 | 38.0" | 99 | 5.181 | Leo |
| Saturn | 5th May 2016 | 16h 55m 18.8s | -20d 47m 03.6s | 0.2 | 18.2" | 100 | 9.141 | Ophiuchus |
| Saturn | 15th May 2016 | 16h 52m 37.9s | -20d 42m 34.3s | 0.1 | 18.3" | 100 | 9.071 | Ophiuchus |
| Saturn | 25th May 2016 | 16h 49m 39.2s | -20d 37m 45.1s | 0.1 | 18.4" | 100 | 9.028 | Ophiuchus |
| Uranus | 5th May 2016 | 01h 20m 53.3s | 07d 53m 01.8s | 5.9 | 03.4" | 100 | 20.888 | Pisces |
| Uranus | 15th May 2016 | 01h 22m 50.5s | 08d 04m 35.8s | 5.9 | 03.4" | 100 | 20.811 | Pisces |
| Uranus | 25th May 2016 | 01h 24m 39.2s | 08d 15m 14.2s | 5.9 | 03.4" | 100 | 20.711 | Pisces |
| Neptune | 5th May 2016 | 22h 52m 34.5s | -08d 02m 53.1s | 7.9 | 02.2" | 100 | 30.396 | Aquarius |
| Neptune | 15th May 2016 | 22h 53m 16.1s | -07d 59m 01.0s | 7.9 | 02.3" | 100 | 30.240 | Aquarius |
| Neptune | 25th May 2016 | 22h 53m 46.5s | -07d 56m 19.0s | 7.9 | 02.3" | 100 | 30.075 | Aquarius |